Weed Seed Growing Slow

7 Reasons Why Cannabis Plants Grow Slow Why are plants staying small? You plant your seeds, seedlings appear, but plants are growing soooooo slow. It’s a common problem with seedlings and When your cannabis plants are growing slow or not at all, there is a reason for it. Find out about the top 10 reasons for slow cannabis growth. If you feel like your plants are not growing as fast as they should then it’s most likely there’s something wrong, slow growth can be a result of a

7 Reasons Why Cannabis Plants Grow Slow

Why are plants staying small? You plant your seeds, seedlings appear, but plants are growing soooooo slow. It’s a common problem with seedlings and vegetative plants, but often frustrating to figure out the fix. What’s the cause? How do you make plants grow faster?

This tutorial will help you overcome the 7 main causes of sluggish growth, so your cannabis plants grow blazingly fast!

You’ll learn how to make plants grow fast and healthy

Note: This article is about slow-growing seedlings and vegetative plants. If you’re in the flowering stage, check out these articles about buds taking forever to mature, increasing yields and improving bud density.

7 Most Common Reasons Plant Growth is Slow

Here are the 7 most common reasons your seedlings or young plants are slow-growing:

1.) Grow Light

Plants tend to grow slow if they’re not getting enough light overall. If slow growth is combined with long, lanky seedlings, your plants need more light. In that case, either increase the power of the light, bring it closer, or get a bigger grow light.

Tall seedlings need more light (grow light is too far away)

You can also give plants too much light. Powerful grow lights cause stress and can slow down plants if they’re kept too close.

Too much light (when the grow light is too close) results in stress and unusual symptoms that can slow down plants

2.) Extreme Environment

Cannabis plants enjoy a warm sunny day. Not too dry, not too humid. Similar to humans, actually. Certain strains are more resistant to an extreme environment, but plants grow best in moderate humidity and warm-but-not-hot air. A good temperature range is warmer than 70°F (21°C) at night and around 79°F (26°C) during the day. Humidity around 50% is perfect.

  • Cold daytime temperatures below 60°F (15°C) may slow growth down to a crawl, and freezing temperatures can kill.
  • Heat above 85°F (30°C) can also slow down growth or even slay plants if it stays too hot for too long
  • Dry air under 35% RH can limit growth, and under 25% RH you may even start seeing signs of deficiencies on the leaves and other odd symptoms
  • High humidity above 70% can make plants droopy and slow down growth by making it harder for the plant to move water efficiently through the plant

Seedlings have the most trouble dealing with a poor environment, while older plants tend to be more resistant to temperature and humidity.

This seedling is struggling to cope with a hot, dry environment. For the fastest growth, keep the temperature around 79°F (26°C) during the day and a little cooler at night. Optimal humidity is around 50%.

Cold temperatures can also stunt plants or make them grow at a snail’s pace. This plant experienced a cold night under 50°F/10°C and was droopy the next morning. It took several days for the plant to recover and start growing normally again. To make things worse, cold temperatures cause plants to drink less, so they’re more likely to suffer from symptoms of overwatering when the temperature falls.

Note: Although fans help equalize the temperature of your grow area, too strong a breeze can slow down seedling growth. Leaves should be gently rustling but you shouldn’t see stems waving around in the wind. If that happens, turn down the fan or point it in a different direction. Learn more about fans and circulation.

3.) Unhappy Roots

Unless you’re growing in a hydroponic setup, chances are your plant roots are hidden from view. Yet roots affect plant growth just as much as the environment aboveground. When the roots are unhealthy or unhappy, a plant languishes and stops growing. When roots are getting what they need, a plant can grow inches a day.

Unhappy roots = Unhappy plants

The most common cause of unhappy roots is overwatering, especially for seedlings and young plants. Overwatering is typically the result of giving too much water at a time, or watering too often.

But isn’t water good for the plant? The problem is that roots also need oxygen, which they typically get through air pockets in the soil. If the soil gets waterlogged from too much water without any pockets of air, the roots start “drowning” from lack of oxygen. The lack of oxygen is what causes the symptoms of drooping and slow growth.

In hydroponic growing, oxygen is provided to roots through bubbles. That’s why hydroponic plants don’t get droopy even though their roots live directly in water.

Overwatering is most common when you have a small plant in a big pot because the roots aren’t drinking much yet. Luckily, this can be overcome with proper seedling watering practices. Yet even if you’re watering plants perfectly, a poor draining grow medium (such as thick muddy soil, or a pot without drainage holes) will still trigger root problems and slow growth due to lack of oxygen at the roots.

The following symptoms of droopiness and yellowing are the result of a thick grow medium, small plant in a big pot, and chronic overwatering.

Overwatering – This seeding is almost a month old but it’s stayed small due to being watered too much and too often

Underwatering is less common but may be even worse for seedlings. Underwatered seedlings grow slow, stay small, and often have a dark coloring.

Underwatering – When plants don’t get enough water, they grow slowly and may turn dark green

If your plant stays in a too-small pot without any room to spread out its roots, growth slows and plants stay small. If you start seeing droopiness and deficiencies on a plant that has been in the same pot for a while, it may be root bound (the roots have wrapped around the edges of the container). This causes symptoms similar to over/underwatering but is difficult or impossible to overcome with watering practices.

With a heavily rootbound plant, you may need to transplant to a bigger pot to stop the symptoms. Just remember to avoid disturbing roots during transplant (try to keep roots in a solid bunch and put the rootball directly into a hole in the new medium) so you don’t unintentionally stress the roots from being moved around too much.

Rootbound – This seedling will grow faster and get bigger if it’s moved to a bigger container so roots can spread out

4.) Nutrient Deficiencies

Seedlings started in soil won’t need nutrients right away, as they can find nutrients in the soil. However, if the pH at the roots is too high or low (6-7 pH is ideal for soil), plants can’t absorb the nutrients properly because nutrients take a different chemical form at high or low pH ranges.

Plants grown in coco or hydroponics need to receive nutrients in the water from when they’re seedlings. Because plain water and coco don’t contain significant amounts of nutrients, the only nutrients plants get are the ones you give them. That means if you’re not giving any nutrients, the plants will grow extremely slowly and eventually turn yellow. Coco and hydro growers also need to adjust the pH of their water to ensure nutrients are absorbed properly. In coco or hydro, the optimum range is 5.5-6.5 pH.

If you’re seeing nutrient deficiencies, chances are your plant isn’t growing as fast as it could. This seedling is growing slowly due to an iron deficiency caused by high pH at the roots (it’s also overwatered, which isn’t helping).

5.) Bugs or Other Pests

Unfortunately, plant pests like broad mites, spider mites, thrips, or even a ton of fungus gnats can slow down growth as the plant spends energy repairing the damage. Sometimes growers mistake the symptoms for a nutrient deficiency or other problem. If you’re noticing spots, patches, or anything unusual on your leaves, don’t ignore it!

Here are some common cannabis pests…

Broad mites cause leaves to almost look shiny

Spider mites much on your plants and create small yellow specks all over your leaves. You may also see webbing.

Thrips also make speckles on your leaves, though they appear in irregular patches as opposed to individual specks.

Fungus gnats look like tiny flies buzzing around your soil and usually aren’t too serious. Just water the plant less often. However, in big numbers, they will hurt plant growth, especially on smaller plants. The following symptoms are caused by an extreme fungus gnat infestation.

6.) Genetics & Natural Variation

Genetics make a difference. Some strains simply germinate and grow faster than others. On top of the genetics, seed storage matters. Older seeds tend to germinate slower and plants are often slower growing at first. Seeds stored in extreme temperatures may also be harder to germinate and easier to stunt.

These six autoflowering plants are about 3 weeks old and all different strains. They were germinated on the same day and grown in the exact same environment, yet some are bigger than others. All have been growing quick and healthy without any problems, so the main difference may be genetics.

Even if genetics are the same, you can give the same care and end up with different growth rates between plants. For example, if you take multiple clones and grow them in the same garden, some will grow faster despite the fact their genetics are identical. That’s just the way nature works. So if you’re noticing only one plant growing slowly, while all the others seem fine, that’s a sign you may just have a runt on your hand. It might have nothing to do with you!

Even when plants have the same genetics and are grown in identical conditions, sometimes you end up with runts. That’s a natural part of growing and it may not be your fault.

7.) Sometimes Plants Want to Be Left Alone

Unfortunately, you can “over-love” your plants. Overwatering is so common among new growers because they are trying to give something good to their plants and get a little carried away.

Sometimes plants need to be left alone. There may be days or even weeks where they really don’t need anything from you besides water.

If you’re wondering why plants are growing slowly, yet you’re constantly messing with plants, touching them, bending them, defoliating, etc., you may need to give them a break until they start growing fast again. Fast-growing vegetative cannabis plants can handle almost anything, but when a plant is growing slow you should focus on providing a good environment, just the right amount of nutrients/water, and staying hands-off until it’s recovered.

Sometimes plants just need time to “do their thing”

How to Make Cannabis Plants Grow Faster

Now that you know what may be causing the problem, get the solution. Follow these principles and your plants will be growing inches a day!

1.) Watering

Proper size pots – Much easier to avoid over or under-watering if plants are in an appropriately sized pot. Seedlings grow fastest in small pots where they’re less likely to get waterlogged, while older plants want bigger pots to spread out their roots. What size pot should I use?

Good drainage – Soil or coco should not seem muddy, dense, or thick. Water should be able to drain freely from the bottom of the pot (if there aren’t any drainage holes, you need to add some yourself). Learn about growing in soil or coco.

Good soil or coco has a texture similar to this

Aim for watering every 2-3 days – Giving just enough water at a time so you can water every 1-3 days produces the fastest growth. Watering every day produces excellent growth but you have to be careful not to give too much at a time. It takes a delicate dance to avoid overwatering when watering that often. I recommend aiming for every 2-3 days for beginners since there’s less room for error.

You may only need to give just a little water at a time when plants are small and not drinking much yet.

Plant pots should be feeling a little light and the top soil should be dry or mostly dry by the time you give water again. If you’re giving so much water at a time that it takes 4+ days for your grow medium to dry out, you likely will achieve faster growth by giving less water at a time. However, some growers prefer a hands-off approach to growing and may not mind plants growing a bit slower if it means they get to water less often. If you need to water more than once a day, the plant is begging for a bigger pot! Read the full watering tutorial.

Nutrients and PH – Make sure your plants are getting the necessary nutrients. As far as pH, some growers get lucky and happen to have perfect water for cannabis plants. However, if your plants are struggling and you don’t know why, the pH being high or low is one of the most common reasons. If your plants are struggling and you haven’t checked the pH at all, get a PH Test Kit and do that first. It’s super simple to adjust the pH (just add “PH Up” or “PH Down” to your water), you just need to know how much to add, and you can’t find that out without testing! Learn everything you need about nutrients and pH.

2.) Environment

Humidity – Keep humidity around 50% RH for the fastest possible growth. Plants can grow at higher or lower humidity levels, but some plants struggle because humidity affects how well water moves through the plant. Since each leaf is constantly giving off water vapor, it’s more common for growers to struggle with high humidity than low humidity, but it still goes both ways.

  • Dry air under 35% RH can limit plant growth, and under 25% RH may even cause deficiencies and other odd symptoms
  • High humidity above 70% often makes plants droopy and slows down growth. In the flowering stage, high humidity can cause buds to grow more fluffy.
See also  How To Get Weed Seeds From Bud

If your air is dry, you may consider turning down any fans to help keep humidity pockets near your plants, though that can only do so much. If the air is really dry, you may need to add a humidifier (raises temperature and humidity) or swamp cooler/evaporative cooler (lowers temperature, raises humidity).

If you’re struggling with high humidity, you may need to add an exhaust fan to vent out humid air and bring in fresh air. If your plants are in a grow tent, typically an exhaust fan that’s set up properly can keep the humidity just a little higher than in the room. If the humidity is much higher in the grow space than the surrounding room, that means you need to help equalize the air with an exhaust/intake fan, or by blowing the air around. If the humidity of your actual room is high, no amount of fans can fix that. In that case, you’ll need either a dehumidifier (raises temperature, lowers humidity) or an AC (lowers temperature and humidity) to bring the RH into a better range. Read the full humidity tutorial.

Extra leafy plants tend to raise the humidity of a space because each leaf is constantly giving off water vapor

Temperature – Cannabis seedlings and young plants love when it’s warm but not hot. Plants typically grow the fastest if the temperature stays around 73F at night and 79F during lights-on. Under LEDs, keep it just a bit warmer, 74F at night and 80F during lights-on. Plants can definitely grow well when it’s a bit warmer or cooler, but you tend to get the fastest growth in that temperature range.

Most growers can’t choose the exact temperature down to the degree, so here’s a more realistic temperature chart.

If the environment is nice for you, it’s probably nice for your plants

Gentle Air Circulation – You probably know if it seems stuffy in your grow space. Plants, like humans, enjoy a gentle breeze to go along with their warm, sunny day. Air circulation prevents hot spots while ensuring plants get plenty of access to fresh air. Fresh air contains CO2, which is crucial to photosynthesis (making energy out of light). As a result of fresh air and great air circulation, plants not only grow faster with stronger stems, they are more resistant to white powdery mildew, bud rot, fungus gnats, spider mites, and other unwanted visitors.

Quick Cheat Sheet to Fixing Environment

  • Fans – Fans equalize the temperature and humidity between two areas by moving air around. Just remember that they cannot alter the overall temperature or humidity. For that, you’ll need….
  • Humidifier – Raises temperature, raises humidity
  • Swamp cooler/evaporative cooler – Lowers temperature, raises humidity
  • Dehumidifier – Raises temperature and lowers humidity
  • Air Conditioner (AC) – Lowers temperature, lowers humidity

A great environment produces fast-growing plants!

3.) Optimize Your Grow Lights

Choose a quality grow light and keep it the recommended distance away from your seedlings for the fastest growth. Usually, the manufacturer of a grow light will have instructions on the proper distance from plants. However, sometimes you’ll see signs of light stress and may need to keep lights further away than recommended, especially for younger plants. If the light feels hot on your hand where your plants are, it definitely should be moved further away. Some of the fastest vegetative growth I’ve seen comes from CMH/LEC grow lights with a vegetative bulb, but most grow lights produce great vegetative growth when used correctly.

Grow light tips to produce excellent vegetative growth:

CFLs – Keep CFLs as close as possible while making sure plants don’t grow into a bulb. After plants are established, you can keep CFLs only inches away. Use the “hand test” to determine if CFLs are too close: put your hand at plant height for 30 seconds, if it feels hot the CFL should be moved further away. CFL bulbs with a spectrum of 6500k are best for seedlings and vegetative plants, and 2700k bulbs should be added in the flowering stage.

T5 Fluorescent light (High Output)* – Traditional T5 grow lights are fluorescent lights like CFLs, and similar principles apply. Keep as close as possible without stressing or burning plants. T5s produce more intense lights than CFLs and often need to be kept further away. Follow the manufacturer’s specifications for distance, or start at 12″ away if you’re not sure and move a little closer each day. Use the “hand test” to determine if T5 too close. If the T5 feels too hot for you at plant height, it’s probably too hot for your plants. T5s can even support plants in the flowering stage if you train plants to grow flat and short like the ones pictured here.

*What is an LED “T5” grow light? It’s basically an LED grow light in the shape of a traditional T5. The term “T5″ is based on the width of the fluorescent bulb (5/8”) so labeling an LED grow light as a “T5” is just a marketing gimmick. From what I’ve seen, some brands work well, others not so much, just like regular LED grow lights.

LEDs – LED grow light technology has improved by leaps and bounds over the last decade but especially in the last 2-3 years. There are good and bad brands out there, but many newer LEDs are designed specifically for growing cannabis. The best LEDs produce captivating bud quality and yields, so the brand you choose is important. Since each model is so different, you should always check the manufacturer’s specifications to determine the proper distance to plants. In addition to paying attention to brand and light distance, some LED lamps are configured to be optimum for the vegetative stage, the flowering stage, or an “all-in-one” mix. I’ve found that LEDs configured for the flowering stage (like the HLG 300L R-spec) can get slower growth with young plants, but performs well in the vegetative stage and produces impressive yields/bud quality in the flowering stage. If you have to choose just one LED light, it’s often best to choose one configured for the flowering stage to maximize your yields, even if it does mean plants grow slightly slower at first. An all-in-one LED lamp like the ViparSpectra PAR600 gives you a mix of benefits and allows you to turn on and off parts of the spectrum to tailor the light color to the current phase of life. That helps with faster seedling growth and gives greater flexibility, all-in-ones may not perform quite as well in the flowering stage as a specialized flowering lamp.

Hobby-level LED grow lights at full power typically need to be kept 2-3′ (60-100cm) away from young plants, though some models need more or less distance. Some models can be dimmed for younger plants or heat control. Since every LED model is different, it’s always a great idea to start at the distance recommended by the manufacturer. LEDs can usually be kept closer as plants get bigger.

Metal Halide (MH) – Metal Halide grow lights produce bushy, healthy, fast-growing vegetative plants. Traditionally, indoor growers used MH lights for the vegetative stage to keep plants short, then switched to an HPS bulb for the flowering stage for the biggest buds. As LED technology has improved, MH/HPS lights have fallen out of favor. However, MH/HPS may be a good fit for growers on a budget. Learn how far to keep MH from plants. Note: The bigger sizes (especially 400W and up) can get extremely hot unless you vent out the heat with an exhaust fan.

High Pressure Sodium (HPS) – MH and HPS usually go together. Most ballasts that can take MH bulbs can take HPS bulbs of the same wattage. HPS bulbs produce great yields in the flowering stage, but plants in the vegetative stage grow tall and stretched under HPS no matter how close the bulb is kept. If you have an MH/HPS ballast, get an MH bulb for the seedling/vegetative stage so you produce wide plants with close node spacing. Then swap to the HPS bulb after you’ve initiated the flowering stage. Note: HPS produces comparable heat to MH, which means above the 400W size they almost always need to be vented to control heat. However, the smaller MH/HPS sizes such as 150W and 250W run much cooler.

These plants are tall and lanky because they were grown under a 250W HPS as from seedling to harvest. The grower should have started with a 250W MH bulb in the fixture during the vegetative stage, then switched to the HPS bulb after plants started making buds. View the grow journal.

CMH/LEC – Each model is a bit different, so refer to the specifications from the manufacturer to determine the best light distance to plants. CMH bulbs often need to be kept further away than MH/HPS bulbs of the same wattage. CMH grow lights (also known as LEC) also have two different spectrum bulbs that can be used. The 4000k/4100k bulb (more blue) produces some of the fastest vegetative growth I’ve seen of any grow light. It’s kind of astounding. The one downside is vegetative plants do grow a little taller/stretchier under CMH than under an MH or many LEDs. The 3100k (more red) CMH bulb performs similarly to an HPS, so try to avoid it during the vegetative stage if possible.

These plants were grown under a 315 LEC grow light

Recommended grow lights for a small setup:


  • CFLs: For the vegetative stage get 2 x 40W ‘daylight’ CFLs then for the flowering stage add at least 2 x 40W ‘soft white’ CFLs. This will fully light a small plant. Great choice for small spaces since each bulb is small and can be kept just inches from the plants – $60
  • T5 grow light: Seedlings and vegetative plants go crazy for fluorescent lights. A 2ft 8-lamp T5 grow light is about 2’x2′ and uses only 196W, yet is strong enough to produce several ounces of weed by itself (though you should train plants to stay flat/short for best yields). A T5 has a thin profile and can be kept just inches from the top of established plants as long as you control heat, so it can be a good choice for short spaces as long as you have room for the lamp itself. It also has switches to turn on only some bulbs at a time, so you can dim the light if needed. One of the most popular vegetative lights – $120 (you should also get flowering bulbs if you plan to use this T5 in the flowering stage)


  • 150W MH/HPS – Can be kept 8-10″ from the tops of plants and doesn’t get too hot. Here’s a 150W HPS all-in-one kit and I also recommend getting a 150W MH bulb for the vegetative stage – $110
  • 250W MH/HPS – This size is a good compromise of heat and yields but they haven’t offered all-in-one kits since the rise of the 315W LEC/CMH. You have buy the components separately: 250W ballast, cheap wing reflector (or any MH/HPS reflector), 250W MH bulb, super 250W HPS bulb. View a grow journal with a 250W HPS. – $195


  • ViparSpectra V450 or PAR600 – The V450 runs cool, uses only 200W, and tends to keep plants shorter than some other LEDs for just $140. The PAR600 model gives you more intense light and still is under $250. ViparSpectra lights get the job done and cost less than a lot of other LED models. See a grow journal featuring ViparSpectra. – The 300L does best in a 2’x4’x6′ grow tent and yields 8-16+ ounces (some people have gotten over a pound). See a grow journal featuring an HLG 300. – Fits a 2’x4’x6′ grow tent (or use two for a 4’x4′) and comes with detailed instructions on how to grow weed with them. Great customer support. This super soil guide heavily features our grow with two Electric Sky ES300 LEDs. Here’s what they looked like at harvest.
  • This is by no means a comprehensive list of quality cannabis-friendly LEDs. There are hundreds of great LEDs to choose from online. These recommendations are based on my personal experience using these LED brands for growing cannabis.

4.) Seeds / Genetics

Start with Good Genetics – Start with good seeds/clones for the best results. Old seeds, found seeds, and unhealthy clones can result in slow-growing plants. On top of that, certain strains tend to germinate better or grow faster than others. That means you’ll get the fastest-growing plants if you start with tested genetics from a trustworthy breeder. Where to get seeds online.

Decide what you want – In my experience, the more well-established breeders tend to offer the best strain consistency and fastest-growing plants. Certain seed companies like Barney’s Farm, Sweet Seeds, Seedsman, and others have a good track record for fast vegetative growth in addition to producing great yields and bud quality. Some recommended strains I’ve grown are Gorilla Zkittlez, Pineapple Chunk, and Pink Kush CBD. I’ve found that newer breeders and companies often sell seeds that produce great buds, but plants don’t necessarily grow as quickly. In fact, I’ve found that many American-bred seeds tend to grow on the slower side and produce smaller yields, though there is a much higher emphasis on the buds looking or smelling a certain way. American breeders especially go for sparkle and smell over other considerations. I’ve grown some outstanding American strains from seed, but that extra sparkle and the intense smells are not always accompanied by similar levels of potency. Something I enjoy about the more established European breeders is their seeds typically grow as described, have faster growth, produce bigger yields, and buds have comparable or better potency to American strains (though buds are rarely as glittery or strong-smelling).

See also  Cheap Weed Seeds

5.) Respond Quickly to Problems

Look at your plants for at least a minute or two every day. It’s really easy to overlook problems if you just water them and go. Taking a minute to really look at each plant and its leaves will often reveal problems right as they’re starting.

Take 2-3 minutes each day to look for…

  • Drooping
  • Leaf spots or discoloration
  • Bugs or webbing
  • White patches or mold
  • Curling or twisted growth
  • Yellow or brown leaf tips

Although just pay attention to the overall color and appearance of plants. If your plant seems “off” to you, it probably is.

Check out our Plant Doctor tool for help diagnosing sick plants. We also have a friendly growing community where you can post pictures of your plants and ask questions.

Healthy leaves are green without discoloration. If leaves look sick, don’t ignore it! Figure out why.

As long as you react quickly, you can solve almost any problem without growth slowing down much, if at all.

This article got sooooo much longer than I originally intended, but I think I’ve created a comprehensive tutorial that solves 99% of cases where plants are growing slowly.

Top 10 Reasons For Slow Cannabis Growth

There can be many reasons why your cannabis plant is growing slow or has stopped growing altogether. It could be a factor in your growing environment such as temperature being off, a problem with nutrients, or something else. Let’s look at the top 10 reasons behind slow and stunted cannabis growth.

When you are growing cannabis, you may sometimes think that you have taken care of everything. Then, seemingly out of the blue, you notice that your plant has stopped growing or is only growing slowly. This can happen during all stages of your cannabis plant’s growth—early in the seedling stage or later in the vegetative growing phase. Why won’t your seedling grow? What could be the reason for your cannabis plant developing slower than it should? Here are some of the most common reasons for slow and stunted growth.



Many cannabis growers, especially those new to cultivation, tend to overwater their plants. Overwatering is indeed one of the most common (and lethal) mistakes when it comes to growing weed, and can cause many growing problems as a result. Slow and stunted growth of your plant can be due to nutrient deficiencies, root rot, or infestation, all of which can be catalysed by excess water in the substrate. If you want to water your plant right, don’t do so on a schedule—just when your plant needs it. It is always better to water less often so that the soil can dry out. A good test of whether you should water your plants is to lift the pot. If the pot is heavy and damp, it’s not time; if the pot is light and dry, you’ll know it’s time to water.


Some cannabis growers have a tendency to overfeed their plants, but not giving plants enough nutrients is another culprit of slow growth. If you’re growing with a pre-fertilised potting mix, know that the nutrients in these will normally only last some weeks to a month. After that time, you need to administer your cannabis with phase-specific nutrients to support healthy development, and eventually, robust flowering. However, know that nutrient requirements for your plant can vary. This will depend on the strain that you’re growing, as well as other factors such as temperature and how much light your plant is getting. If you’re growing under intensive grow lights, your plant will need more nutrients than if it were growing under less light.


Low-quality or old cannabis seeds are a common reason for all sorts of growing problems. If you use low-quality seeds, your plant may grow slow and stunted, or your seed may not even germinate at all. For best results, choose only quality seeds like those you can get at Zambeza and other reputable seed banks. With Zambeza Seeds, you will receive the best genetics so your cannabis plant will have a great start to its life, and a much better chance of healthy growth throughout all stages.


Cannabis needs a lot of light, especially in the flowering phase. But your plants will also need sufficient light to support their vegetative growth. Although light requirements may vary between strains, all plants need a baseline amount of light exposure to prosper. If you grow indoors and feel that your plants are not getting enough light, you should be able to simply lower your lights, decreasing the distance between the lamp and the canopy. If you’re growing outdoors, make sure you plant in a spot with a lot of direct sun, or move your pots around throughout the day to maximise sun exposure.


Again, cannabis plants love and require a lot of light; but too much is not a good thing either. Constant direct exposure to intensive sunlight or high-intensity indoor grow lights can stress your plants, which can lead to slow growth and other problems. If you think that too much light is behind the issue and you are growing indoors, move your plants further away from your lights to decrease the intensity. If you’re growing outdoors in pots, move your plants to a location with diffused or partial sunlight if possible.


In addition to the amount of light, the spectrum of light plays an equally important role. Some types of grow lights, those with a warmer, more reddish light spectrum, are more suited for flowering, while other lights can emit a colder, blueish light that is better for the vegetative phase. Make sure that you use a light in the right spectrum, otherwise your plant may grow slower than normal. Many common grow lights today are suitable for both your plant’s vegetative and flowering phases. However, if you are not sure, make sure you read the description for the light or ask the vendor before you purchase.


Cannabis requires many vital elements for healthy growth, and calcium is one of them. If your plant is experiencing a calcium deficiency, it will mostly affect new growth on top of your plant. You may observe symptoms such as slow or twisted new growth, or the leaves turning purple or yellow. In time, your whole plant will take on a sickly appearance.

Although most cannabis nutrients should contain adequate amounts of calcium for healthy growth, a deficiency can still occur. Some growing media such as coco increase the risk for a calcium deficiency. This is also why coco growers normally use special coco nutrients or add Cal-Mag products to their nutrient regimen. You can also add dolomitic lime to your soil to avoid a calcium deficiency.


Along with overwatering or overfeeding, problems with the pH value of the water or nutrient solution are a common reason for slowed growth. Cannabis is rather picky when it comes to correct pH value, and if your plant is not within a healthy pH window, it cannot take up nutrients—even if they are present.

If you grow your cannabis plant in soil, ensure that your water or nutrient solution has a pH value of 6.5–7.0. For hydro, the optimal pH for cannabis is 5.6–5.8. If you grow soilless, including in coco, make sure the pH value for your water sits at 6.0–6.3.


Have you ever wondered why you should start your plant in a small pot and only later repot into a bigger container? The answer is that a tiny seedling cannot absorb all the moisture present in a large pot, which can lead to all sorts of troubles. Mature plants with a large root system won’t have this problem as they can drink much more. One other issue with large pots is that they will take much longer to dry out. And just as with overwatering, the large pot and the stagnant moisture can incite slowed growth and a host of other problems.

Always start your seed in a small container such as a cup or jiffy pot, then transfer it into a larger pot once your plant has a set of 5–6 leaves. If you have already planted your seed in a large pot, make sure that you water only in a small area around the seedling.


Plant height 30cm: 7.5–11l container
Plant height 60cm: 11–19l container
Plant height 90cm: 18–26l container
Plant height 120cm: 22–37l container
Plant height 150cm: 30–37l+ container


Cannabis, like many other plants, grows best at moderately warm temperatures. The optimal temperature range for growing weed is between 25 and 30°C, although nighttime temperatures should be a few degrees lower. If it is too cold, this will slow down your plant’s growth. Likewise, you want to avoid exposing your plants to excessive heat. Temperatures that are too high can also lead to slow growth or halt plant development altogether. If you are growing indoors, make sure that the temperatures are at a comfortable level for your plants and that your grow room is well-ventilated. Sometimes a simple fan can be all that’s needed to get grow room temperatures under control.

No reason to panic if your cannabis plant is growing slow! With our guide, you should be able to identify and address the most common reasons for slow and stunted growth.

How To Deal With Slow Cannabis Growth

If you feel like your plants are not growing as fast as they should then it’s most likely there’s something wrong, slow growth can be a result of a number of things. If your plants are suffering from slow root growth, or you’re asking yourself why your plants are growing so slow, here are a couple of tips to help you fix your problem, remember these problems can affect cannabis in all stages of plant growth.

When growing cannabis there are a lot of variables that can affect the growth and final result of your harvest. From genetics, possible nutrient deficiencies, root system, and pests problems to the environment, you need to make sure everything is okay if you want to have a smooth growth cycle. Providing your plants with a warm slightly humid climate will not only help you to deal with their slow growth but can result in a bigger and better harvest.

1. Lights

Not enough light is one of the main problems associated with slow growth. Not providing enough light will cause your cannabis to take way longer to develop because they don’t have a good amount of light to photosynthesize. When your plants are still young you can see this, for example, when your seedling is stretching too much, this is a sign that your plant is not getting enough light and is trying to get closer to it.

Now, have in mind that you can also give your cannabis too much light (if the environment is not appropriate for the amount of light you’re providing). This happens because most high-intensity lights have to be used in combination with higher CO2 levels so your plant can absorb the light properly, if the CO2 level is too low your plant can get stressed and show heat stress signs, resulting in slow growth.

How to deal with it

If you’re experiencing light-related problems (like heat stress symptoms), you should try to adjust the intensity (with a dimmer) or the height your light fixture is at. A good way to test this is to keep your hands under the light for around 30 seconds, if it’s too hot for you, it definitely is too hot for your plants.

As a general guide, LEDs should be kept between 60-100 cm from your plants (depending on the model) while light bulb fixtures should be around 30cm from your canopy.

Incorrect Light Spectrum

The light spectrum will also affect plant growth so you need to make sure to use the right spectrum for each stage of plant growth. This doesn’t mean your plants won’t grow under a different spectrum but if you want your plants to grow fast and healthy, make sure to provide a blue spectrum during the vegetative stage and a red spectrum during the flowering stage.

Interruption of the Light Cycle

Photoperiod cannabis is really sensitive to light leaks during the light cycle. You always have to there are no holes in your tent where light from the street lamp, for example, could leak in. Light leaks can not only turn your plants’ hermie but can also cause a hormone imbalance that could reveg your plants, which will end up extending your grow cycle, and affect yields and quality. So if you’re having issues with light leaks make sure to check out autoflowers as they are not affected by light leaks because they flower based on age and not the light cycle to do so.

2. Stress From Accidental Damage

If your fan or light fixture accidentally falls over your cannabis, there could be some serious problems such as broken branches or even worse, and this can slow down growth significantly. When any type of damage occurs, your plant will have to move around nutrients and vitamins, for example, to the areas that need it the most, meaning that your cannabis will redirect the resources needed for new plant growth to repair the damage.

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In most cases, your plant will most likely slow down growth for a couple of days until it finished recovering and can continue growing normally. Just remember that seedlings are super fragile so double-check the equipment and make sure everything is hung up properly before starting your grow cycle.

How to deal with it

There’s not much you can do if your cannabis has suffered an accident, so first make sure you know what caused it. If a branch snapped due to strong winds you can use bamboo stakes or a scrog net to provide support; If a piece of equipment fell on your cannabis and broke a branch, all you can do is try to fix it with duct tape to help it hold it in place until it heals and check the equipment before starting your next grow cycle.

3. Low-Stress Training

Plant training is used by almost all cannabis growers to adjust plant growth and end with the best results possible in a specific grow setup but it may end up having the opposite result if done too aggressively and slow down growth. As the name says, low-stress training will stress your cannabis, but not as much as high-stress training, this allows you to do it more often if needed, but you will have to keep an eye on your plant and keep good conditions to minimize stress.

LST is an easy and effective way of molding plant growth to your grow tent but even minimal training such as pruning can be bad.

For example, pruning a lot at a time or very frequently will cause your plant to slow down growth in order to recover and this can be very bad, especially with autoflowers because it may end up stunting growth for days or even weeks, so make sure you do it gradually and carefully.

This also applies to tying down the branches or simply organizing the canopy under a scrog net, if you apply too much pressure or tie the branches too tight you may end up hurting your plant and this will cause stress so make sure you do it carefully.

How to deal with it

Luckily, it’s can be easy to help your plant recover from slow growth, f you’ve pruned too much there’s not much you can do other than making sure the growing conditions are on point to allow your plant to recover faster but, if you were LSTing and the ties are too tight, you can remove them and tie them again, paying attention to what you’ve done incorrectly before to avoid doing it again.

4. High-Stress Training

You can end up damaging your cannabis with low-stress training techniques as well as with high-stress training techniques, although it may be easier to damage your plant with HST because it literally consists of mutilating your cannabis plant.

High-stress training consists of mutilating your plant so always make sure your plants is healthy before performing it.

Now, this doesn’t mean that your plant will only get stressed if you mutilate it, as said above you can also stress your cannabis with low-stress training.

Just remember that HST will always slow down growth because you are cutting away a part of the cannabis plant so make sure you do it early rather than late and that the conditions are on point so your cannabis can recover fast and continue growing normally.

How to deal with it

Now, when dealing with the recovery period after LST or HST, the only thing you can do is provide the best growing conditions possible to boost the basic processes such as transpiration and photosynthesis, this will allow your plant to recover faster.

If you’re not sure what the conditions should be, you can always take a look at a VPD chart to ensure you’re providing what your cannabis needs but other than that, it’s just a matter of seeing how your plant reacts and maybe not performing any training if your plant is in bad conditions.

5. Environment

Even though some plants can withstand harsh environments, most cannabis plants enjoy a warm slightly humid climate, it’s essential you have a thermo hygrometer to measure this and adjust when necessary and avoid stunted growth. If the temperature in your grow room is below 15°C or above 30°C for too long, you will start to see slower growth and if left like that for too long, you’ll see signs of unhappy cannabis like droopy leaves or the leaves starting to yellow, crisp and die.

The ideal humidity levels are around 60% for seedlings, 50% in the vegetative stage and 40% in the flowering stage.

This also applies to humidity. Humidity levels below 35% can stunt growth and if they’re even lower than that (around 25%), you’ll start to see signs of deficiency on your plant.

A humidity level higher than 70% can also have a toll on your cannabis plant, slowing your plant’s growth, making them droopy because it makes it harder for the plant to move water internally.

How to deal with it

If your seedlings are not growing or you’re wondering why your seedlings are growing so slow, this could be the problem. To avoid environment-related problems you have to ensure your growing environment is optimal for your cannabis.

For your cannabis plants to thrive you need to provide a temperature of around 22-25 celsius and a humidity level of 60% for seedling, 50% in the vegetative stage, and 40% in the flowering stage.

Stage Humidity Level
Seedling 60%
Vegetative 50%
Flowering 40%

These numbers are just a guideline, you should always look for the signs your plants give you and adjust the environment accordingly.

6. Root problems

Unless you’re growing in a hydroponic (or aeroponic) setup you won’t be able to see your plant’s roots.

Keeping a good environment for your cannabis also includes maintaining the medium oxygenated and with the right amount of water. Root problems are the main cause of slow growth with new growers, adjusting and maintaining a good growing medium for the roots is the best way to fix stunted growth in plants. The lack of appropriate care with the roots can cause the following problems:


Overwatering is a common occurrence with new growers, excessive watering inhibits oxygen from reaching the roots and can result in the drowning of your plant.

Overwatered plants will start to droop, show slower growth, start yellowing, and show signs of deficiencies because they can’t absorb nutrients properly.


Underwatering isn’t as common as overwatering but can also affect your plant in a bad way.

If there’s a lack of water in the medium, your plant will show signs similar to the signs of overwatering but instead of the leaves looking “fat” because of the excess of water, they will look thin and fragile because there’s no water (or a tiny amount) in them.

Oxygen is essential to the roots, by providing the appropriate amount of oxygen in the medium, you allow the roots to develop healthy, resulting in a healthier plant.


Rootbound happens when you plant your seeds in a small pot or container and the roots don’t have any more room to grow. When this happens, your plant will start to show different symptoms that can confuse you, when you see your plant getting much wider than the pot you should start thinking about transplanting it, failing to give the roots the space they need to grow will result in droopy leaves and other signs associated with overwatering of nutrient deficiencies.

How to deal with it

To avoid root problems you have to make sure you’re giving the roots enough oxygen, room to grow, and water only when needed. You should water only when at least 60% of the medium is dry and transplant your cannabis when she’s growing out the pot she’s in. If you’re having problems with this we recommend you try different mixes of soil, perlite, and coco fiber, this will help you provide the right amount of oxygen and water to the roots.

7. Nutrient deficiencies

Plants need nutrients to grow, depending on the medium you’re growing in, you’ll need to not only provide all the macronutrients but also a good amount of micronutrients. You also have to remember that nutrient absorption is directly related to the pH level.

If you don’t provide the amount of nutrients your plant needs or if you fail to adjust the pH level your plant won’t be able to grow properly and will result in nutrient deficiencies, stunting growth, and damaging the leaves.

How to deal with it

To fix this you need to adjust the amount of nutrients you’re giving your plant and check the pH level every day.

If you’re giving the right amount of nutrients then the problem will most likely be the pH level, remember the pH level changes according to the medium you’re growing in and you should always check it and adjust it if you want your cannabis to grow healthy. It is crucial you keep your plant well-fed and with the correct pH levels, if you see even the slightest yellowing on the leaves then your plant is most likely not growing properly.

8. Bugs or pests

Bugs and pests feed on your plant, they can feed on the sugars or on the plant matter, either way, they will damage your plant and slow its growth. Some bugs like Spider mites can also rot the buds, making them unhealthy to smoke so it’s crucial you keep your plant healthy and check on them every day to spot bugs early.

How to deal with it

There are different ways to deal with bugs but the best way is to prevent them.

By checking on your plants every day you avoid bugs, you can also spread yellow sticky traps so you can spot them early.

You can also spray your cannabis with a mix of water and a small dose of organic insecticide to prevent them although this is not recommended, insecticides should only be used when you already have bugs and are used to eliminate and not to prevent them.

9. Genetics

Slow plant growth can also be the result of bad genetics, even though you cannot change this once you’ve already started to grow your plant, you should always start with good genetics. This will save you time and money and can result in a bigger and better harvest.

How to deal with it

If you’re dealing with slow plant growth and can’t seem to get to the root of it, the cause of your problems can be bad genetics. If you want a plant that really thrives and grows perfectly we recommend our new Gorilla Cookies Auto.

I got 134g off this gal growing in 3 gal pot with 24 hours of light. i’m stoked with the result! Smells like diesel. Was a great grow overall.

This strain is very easy to grow and can produce up to 600gr/m2 of extremely resinous buds with basic maintenance, so with basic care you can end up with a great harvest.

10. Incorrect pH Levels

Incorrect pH levels are probably the most common reason for slow growth. This happens because cannabis plants can only absorb nutrients in a specific pH range so if the pH levels are incorrect your plants will not be able to absorb food, even if it’s present in the substrate.


In order to fix this, all you have to do is check and adjust the pH levels, but this depends on the specific substrate you’re growing in. Remember that you will also need a pH Up or pH Down solution, but all you have to do is adjust the pH to 6.5 – 7.0 in soil, 5.6 – 5.8 in hydro, and 6.0 – 6.3 in coco fiber or soilless grows.

11. Pot Size

In general, growers start seeds in plastic cups and transplant them to bigger pots as the plants grow but starting your plants in super big pots can cause several problems such as overwatering as the substrate which will retain much more water than your seedlings can absorb. SO to avoid problems like this, make sure to start in smaller pots or plastic cups and only transplant them to a larger pot once they have big enough. In general, you should only transplant a young plant into a 7-liter or bigger pot once they have developed at least 5 pairs of true leaves.


As mentioned, the only way to avoid this is to use the right pot size, so once your seedling is big enough, follow the table below and make sure to transplant directly to the right pot in order to avoid any issues.

Recommended Pot Size Based on Plant Size
Pot Size Plant Size
3 liters 35 – 50 cm
5 – 7 liters 60 cm
8 – 10 liters 100 cm
12 liters +130 cm

12. In Conclusion

It’s fairly common to deal with cannabis stunted growth, especially if you’re dealing with a cannabis seedling growing slowly. Slow plant growth, either slow cannabis flowering or vegetative growth, can be the result of a not-optimal growing environment or even a mix of some of the elements said above.

So if you’re dealing with cannabis slow growth or if you’re having problems with your plants, we recommend checking every one of the topics we talked about and if you cannot solve your problems try to grow good quality genetics in your growing cycle. This can not only solve your problems but surprise you with the results you’ll have.