How to Prevent and Fix Leggy Seedlings
Are you new to growing vegetables, herbs or flowers from seed? Have you ever wondered what’s up with the term “leggy seedlings”? Or, do you have some freshly-sprouted seedlings that are looking extra lean and tall? (Spoiler alert: they might be leggy!) If you answered “yes” to any of these questions, then you’ve come to the right place. This article will teach you everything you need to know about leggy seedlings: what they are, why they’re a bit of a problem, how to prevent them, and even how to correct leggy seedlings once they grow!
Be sure to also stop by our Seed Starting 101 article for more tips on raising the most robust seedlings possible.
What are leggy seedlings?
Seedlings are described as “leggy” when they grow very tall, skinny, and lanky. In the seedling world, taller does not equate to better, healthier plants! On the contrary, thin leggy seedlings are typically quite weak and fragile. They may also be pale or yellow-looking.
There is no exact height that seedlings must surpass to officially classify as leggy. It’s more about comparing them to healthy seedlings of the same variety that are grown in ideal conditions, which will stay much shorter compared to their less-happy, leggy counterparts. With time and experience, you’ll get a feel for what is considered grossly leggy or not.
What causes leggy seedlings?
The primary cause of leggy seedlings is lack of sufficient light, either in brightness or proximity to the plants. This can happen when gardeners start seeds indoors, or when seeds are planted outside in a too-shady location. Even in our greenhouse (which is partially shaded in the afternoon) we need to use grow lights in order to keep our seedlings happy. Paired with being stretched out tall, leggy seedlings will also often lean to one side – towards the direction of the brightest source of light around. They are desperately reaching for the sun!
Are leggy seedlings bad?
In general, a leggy growth pattern on seedlings is not ideal. Rather than focusing their energy on developing thick, strong, sturdy stems, leggy seedlings become increasingly thin, fragile, and weak the taller they become. Their top-heavy nature makes them more vulnerable to flopping over, breaking, or other damage. Especially in the face of wind or other elements. Leggy seedlings are also more prone to ‘damping off’ – a condition when seedlings suddenly wilt, become very thin or rot right above the soil line.
Come planting time, not all types of seedlings like to be buried extra deep to compensate for their leggy stems. That practice also comes with the risk of rotting stems. However, many leggy seedlings can be saved (see “how to fix leggy seedlings” below). Tomato and tomatillo seedlings are particularly forgiving. Packed in a tight bunch and harvested young, it also doesn’t really matter if homegrown microgreens become leggy.
All in all, it is best practice to try to prevent leggy seedlings in the first place. Follow the tips below!
How to Prevent Leggy Seedlings
Provide ample bright light to seedlings immediately after germination. All it takes is a day or two in the dark for a young sprout to get irreversibly leggy!
When starting seeds indoors, plan to provide seedlings with supplemental light (aka a “grow light”). Unfortunately, a sunny window generally doesn’t provide enough light on its own.
As soon as your seeds sprout, turn the grow lights on. If you’re worried about missing this crucial moment, turn on your grow lights a few days after sowing seeds (but before they’ve sprouted). The vast majority of seeds do not need light to germinate, but that way the light will be on and waiting for the moment they do!
Remove any cover used over your seed starting tray to aid in germination (e.g. humidity dome or other) soon after the seedlings sprout, especially if it is not transparent.
Keep grow lights suspended low over the seedlings. Even with a very bright grow light, seedlings may get leggy if it’s hung too high. Most fluorescent lights can stay as close as a few inches above seedlings, while LEDs usually need to be kept higher to avoid burning the plants. Follow the light manufacturer’s recommendations. Raise the lights as needed as your plants grow taller.
Provide a minimum of 12 hours of bright light (14 to 16 hours is ideal) and 8 hours of darkness. I highly recommend using a simple light timer! Set it and forget it.
Learn more about choosing and using grow lights in this article, which covers the key differences between LED and fluorescent lights, ratings, best practices, and popular grow light options.
How to Correct or Fix Leggy Seedlings
Once you have leggy seedlings, there isn’t anything you can do to make them short again. However, if you act quickly, you may be able to prevent them from becoming even more lanky. Furthermore, there are a few tricks to help them gain strength and still live out their best life possible.
1) Provide more light as soon as possible
The best way to fix leggy seedlings is give them more light, ASAP! This could mean adding a supplemental grow light if you’re not using one already, upgrading to a stronger light, or lowering your current light closer to the seedlings so it is more effective. As you lower a light, there is a smaller area of well-lit space available below it’s canopy. Thus, it may require several lights or one larger unit to provide adequate light over a large number of seedling trays. Otherwise, the stragglers around the perimeter are left out! In that case, take turns rotating different trays directly under the light every day until you can provide more.
2) Turn heat mats off (or down)
If you are using a seedling heat mat to start seeds indoors and your seedlings appear to be getting leggy, go ahead and turn the heat mat off or down. Warmth helps to expedite seed germination (a great thing!) but can also encourage seedlings to grow faster. When seedlings are already lookin’ on the leggy side, let’s not do anything to encourage them to get even taller, shall we? This recommendation comes in addition to adding more light of course.
We personally love to use these seedling heat mats that have a built-in thermostat control and temperature probe. After germination, we set our heat mats to come on only when the soil temperature drops below 65-70°F. This keeps our heat-loving summer crop seedlings (tomatoes, peppers, basil, flowers, etc) happy in our greenhouse during the winter to early spring, where it can get quite chilly overnight but also very warm during the day. You can easily apply the same set-up indoors, in a garage, or anywhere you’re raising seedlings.
3) Start over
Okay, hear me out here. I’m not talking about starting a new round of seeds when you’re several weeks or even months deep into the seed-starting season for your zone. However, if you have ample seeds and things are looking leggy only a few days after germination, it might be in everyone’s best interest to start fresh rather than fussing over leggy seedlings for the rest of the season.
For example, just the other day I started a few 6-packs of bok choy seeds on a heat mat in a dark spare room. I had every wonderful intention of checking them frequently and moving them out to the greenhouse (and under a grow light) as soon as they sprouted. Welp, I forgot to check on them for over 24 hours, they sprouted, and already looked way too tall for my liking. So I simply started more bok choy seeds, and kept the leggy seedlings as the ‘bad example’ for this post!
4) Make them stronger
If you have leggy seedlings, you very well might be able to plant them anyways! But first, they need to be significantly strengthened in preparation. Early on, they’ll be too weak to plant outside. Also, young leggy seedlings are usually too tender to bury deeper in soil without the stems potentially rotting.
Be sure to thin your seedlings down to just one sprout per cell or container within a couple weeks after sprouting. Thinning reduces competition for nutrients, space, light, water, and improves air circulation. I always suggest trimming out unwanted sprouts rather than plucking and pulling. After that, there are three main ways to turn your leggy seedlings from puny to mighty:
To strengthen seedlings, introduce a light wind with an oscillating fan. Don’t put it on full blast, but enough to create gentle shaking and movement. Movement helps the stems of leggy seedlings become more tough and strong. Tickling seedlings with your hands can help in the same manner. Yet a fan is beneficial in more ways than one! Ample airflow also prevents fungal disease and damping off. I recommend using a fan on indoor seedlings whether they’re leggy or not.
Use mild fertilizer and “water from below”
Another way to boost the health of leggy seedlings is to feed them! Once seedlings develop their first set or two of true leaves (the ones that grow after the initial two leaves that are often heart-shaped) you can begin to feed them with a very mild liquid fertilizer. The seedlings should be at least a few weeks old by this point, since they do not need or care for fertilizer much younger than that.
We prefer to feed our seedlings with seaweed extract, though fish emulsion is another popular choice. Be sure to dilute whatever you use per the instructions on the bottle. Then, add the liquid fertilizer/water into the lower tray that the seedling containers are sitting in. The soil will soak up what it needs from the bottom. That is the way we always suggest to water all seedlings anyways, but especially the leggy ones! Pouring water in from the top runs the risk of knocking them over, and doesn’t provide even moisture. When you water from below, it encourages their roots to grow deep – making the plants more strong.
Finally, be sure to always harden off leggy seedlings before transplanting them outside. ‘Hardening off’ is the process of slowly introducing seedlings that were raised indoors to the outdoor elements. This generally involves taking the seedlings outside each day over the course of a week, starting with just a few hours in the shade and gradually increasing the time and amount of direct sunlight. Like a fan, this makes the seedlings stronger and more prepared to face challenges such as wind, rain, hot sun, or cold conditions. See step-by-step hardening off instructions here.
Potting Up or Planting Leggy Seedlings
Can you bury leggy seedlings deeper in the soil?
Generally, yes, you can plant leggy seedlings deeper in the soil to help compensate for the extra-long stems! However, avoid the temptation to plant them deeper right away, when they’re still very young and tender. Weak, thin, small stems may rot once they’re buried in damp soil. Wait at least several weeks, and after taking steps to strengthen and/or harden off the leggy seedlings as described above.
Once the stems are more tough and strong, you should be able to bury a portion of the leggy seedling stem – either by potting them up, or transplanting them outside. Or, you may do both! For instance, we start our tomatoes in small 4” seedling pots. Then after about a month, we pot up the seedlings into larger 8” nursery pots and bury the stem by a couple inches at that time. Then when we transplant them out into the garden, we can bury the stem a few more inches if needed.
How deep can you plant leggy seedlings?
Well, that depends on the type of plant and size of the seedling! The goal is to bury the leggy seedling stem enough so that the plant isn’t too top heavy and can successfully grow. Otherwise, I personally err on the side of caution and avoid burying them more than necessary.
Most common garden vegetables don’t mind if you bury their stem part way or all the way up to theirfirst set of true leaves (or first set of lateral branches). You can do this with peppers and members of the brassica family: kale, collard greens, broccoli, Brussels sprouts, or cauliflower.
If the vegetable is one that should normally form a head or bulb right at the soil line, then you’ll want to bury it up to that point – where the stem branches and begins to form the main crop, so that its weight will be supported on the soil surface. Consider a head of lettuce, bok choy, cabbage, or kohlrabi for example.
You can plant some seedlings even deeper. Tomatoes and tomatillos are prime examples. Due to their advantageous root systems, it is a common practice to remove the lowest few branches and bury leggy tomato seedlings up past that point (planting up to half of the plant underground). Tomatoes and tomatillos will grow new roots off of the buried portion of the stem! More roots equals a more robust and healthy plant.
It is less necessary to deeply bury seedlings of plants that will continue to grow tall branching stems well above the soil line anyways, such as flowers or herbs.
And that concludes this lesson on leggy seedlings.
All in all, do not feel bad if your seedlings are a little leggy! Even the most experienced gardeners doing all the “right” things grow some slightly leggy seedlings sometimes – ourselves included. As you saw in this article, all hope is not lost! There are a number of ways to prevent and fix leggy seedlings. Plus, you’ll learn from your mistakes and improve next season. That is one thing I love about gardening: there is always something new to learn, and there is always next year.
Please let me know if you have any questions in the comments below. Also, please pin or share this article if you found it valuable! Cheers to growing happy seedlings!
Come learn what causes leggy seedlings plus how to prevent and fix them, so you can grow the most healthy and strong plants possible!