Harvesting Weed Seeds

How to grow cannabis in summer after a late start. Read our full guide on germinating cannabis seeds in July and growing cannabis in the summer. Weed control, management, ecology, and minutia Seed shattering refers to the natural shedding of seeds when they ripe, a phenomenon typically observed in wild and weedy plant species. The timing and extent of this phenomenon varies considerably among plant species. Seed shattering is primarily a genetically controlled trait; however, it is signi …

Can I start seeds in July and harvest in October?

Yes you can! Although most growers would, perhaps correctly, point out that a July start is a little late if you are aiming for maximum yield. Many outdoor growers would hope to germinate their cannabis seeds a couple of months earlier than July in order to give their plants the best chance of reaching their true genetic potential.

That said, you can germinate your seeds in July and still get a good quality harvest. If you are interested in knowing more about how to grow cannabis in summer, even after a late start, we have some great tips and info.

“When is it too late to plant cannabis for summer?” is a common question from outdoor growers. The answer depends partly on your local climate and the type of cannabis seeds you are hoping to grow.

With some expert advice on the best type of seeds for your situation (autoflower seeds vs feminised seeds), growing cannabis in summer is very straightforward. Lots of people get great results and so can you!

Pros and cons of starting cannabis seeds in summer

The summer solstice (longest day) is June 21st (Northern Hemisphere) and December 21st (Southern Hemisphere). Regarding the summer solstice, cannabis is generally recommended to be planted outdoors before the solstice. This remains good advice, but for many growers it is also possible to plant your cannabis seeds after the summer solstice and still get a harvest in the autumn/fall.

Advantages of seeding cannabis in July for northern Hemisphere growers (or January for Southern Hemisphere growers):
  • The warm summer weather has already arrived, your growing season is already here!
  • No risk of losing your seedlings due to an unexpected late frost.
  • Guerrilla growers will already have lots of wild plants growing rapidly, perfect to hide your cannabis plants behind!
  • There is still time left for a harvest, even if it’s a slightly shorter remaining grow season.
  • You can look forward to seeing your plants thrive outdoors immediately in the mid summer conditions.
The disadvantages of starting cannabis seeds in July also need consideration:
  • In general, your soil will be drier for your seedlings. Root growth is more difficult in dry soil so watering needs to be more frequent while the plants are young and more vulnerable to the heat.
  • Black plant containers can become extremely hot in direct sunlight. In the worst cases this will bake the root ball, dehydrating the soil and the plant. This can kill the plant within a day or two. Keep plant containers in the shade, perhaps wrapped in a reflective white cover. Avoid putting plant containers on hot tiled surfaces.
  • Plants germinated late in the season will likely be smaller than they would have been with an earlier start. This will mean smaller yields.
  • Young plants may not cope well with direct midday sun in the hottest part of summer. Consider living them some shelter/shade from the sun between midday until around 4-5pm in extreme conditions. Perhaps under a tarpaulin or similar.
  • With a short vegetative period the root network of your plants won’t be as deep or extensive as it would have been with a long vegetative period. This means you will need to give extra consideration to watering your plant more regularly.

How to grow cannabis outdoors in summer

Look for a private area where you can plant your cannabis seeds and allow them to develop without risk of discovery. Outdoor cannabis growers often have several guerrilla grow locations, just in case one of them is discovered. Unused field corners, waste urban land, river banks, hillsides etc all make great potential locations.

If local soil quality is poor you can supplement it with supermarket soil, well-rotted manure, general fertiliser etc. You can easily make a cannabis organic summer soil mix by blending some quality compost with some slow release organic nutrients such as those from BioTabs. Or you could add your own ingredients to enrich local soil e.g. bone/fish/blood meal, seaweed, worm castings, bat guano etc. If you can grow cannabis on your own land, balcony or patio that makes it easier to monitor plant development.

“How often should you water outdoor cannabis plants during summer” is another common question. In times of hot weather it is normal to water both at morning and night. If you use a larger plant container the roots have a larger available root space of moist grow medium which will allow your plant to manage for longer periods with watering.

If you root your plant directly into the moist earth (without a container) it allows you more latitude, you may need to water less frequently since the roots can source their own water unless in severe drought. When growing in containers you can assess the remaining moisture levels by lifting the container (if possible) to assess the weight. Or you may prefer to use a hygrometer in your plant container to measure moisture level in the root zone.

Growers in extremely hot regions often ask whether will cannabis grow outdoors in summer, in the south with hot temperatures. Unless temperatures are regularly hitting 35-40ºC for prolonged periods then you should be able to get the plants through to harvest.

Planning your grow after a late outdoor season start

If you are aiming to plant cannabis seeds in the summer, most growers aim to get their plants outdoors as soon as the weather is suitable. For growers in northern Europe that can mean waiting until the last frost has passed.

  • At Dutch latitudes, or similar, growers often put their plants outdoors around late May.
  • At southern Mediterranean latitudes you might place your seedlings outdoors in March.
See also  Parable Of Seeds And Weeds

Obviously, an earlier start allows your photoperiod feminised outdoor strains a longer period of vegetative growth and therefore a larger final result. But that doesn’t mean that you can’t start your feminised seeds in July, and accept a somewhat smaller final result.

Autoflowering cannabis seeds are generally recognised as being the fastest, simplest and easiest way to grow cannabis. They can grow from seed to harvest in around 3 months.

Having a spare pack of autoflower seeds in the fridge is always a good idea for outdoor growers contemplating a last-minute summer grow. Check out the Dutch Passion Seed Sale for the latest special offers.

Choosing the best suited seeds for a summer cannabis grow

If you’re planting your cannabis seeds in June or July you need fast growing outdoor strains. Autoflower seeds are particularly recommended for outdoor growers thinking of a late start.

If you plant your auto seeds in June (or early July) you should have a crop around late September or early October. If you can pre-grow your auto seeds indoors for a couple of weeks (under 24 hours of daily light) before planting them out that will speed up your plant development and final size even more.

Choose the faster autoflower strains if you are up against the clock with a late season grow. Some longer blooming autos (e.g. Auto Ultimate, Auto Glueberry) can take a few weeks longer than average, such autoflower strains are probably best avoided if you are on a tight schedule.

Recommended fast/tough auto strains include Auto Mazar, Auto Blueberry and Auto Blackberry Kush. All will do well outdoors and are fast enough to deliver a harvest even if planted outdoors late in the year.

Photoperiod feminised strains are also a good choice for a late season outdoor grow. Dependable strains such as Frisian Dew, Think Fast and Durban Poison are all recommended.

However, it should be noted that photoperiod feminised outdoor cannabis seeds germinated in July will only have around a month of vegetative growth before starting bloom. This will have inevitable consequences on size and yield. Expect a small/medium sized result rather than a monster outdoor plant.

Watering and feeding schedule for outdoor cannabis in summer

Watering requirements when growing in the middle of summer can be high. Growers in Southern Europe may see heatwave temperatures in excess of 30ºC for long stretches. This can mean watering your plant at morning and night. Some growers leave some water/nutrient solution in a tray underneath their plant container.

This can help the plant from completely drying out. Some growers remove their plant from direct sunlight in the middle of the day, or place the plant in shade to protect it from the worst of the midday heat.

Growers in cooler climates (e.g. Northern UK, Scandinavia) may still face hot temperatures though rarely as high and prolonged as those faced by growers with more Mediterranean climates. Watering and feeding schedules for growers in these regions will vary significantly.

Whether you are growing in a hot or a cool climate you will need to find the right watering schedule for your conditions. Even in the same grow location, outdoor conditions can vary significantly from one year to the next.

Flowering cannabis plants seeded in July

Autoflower seeds germinated in July (Northern Hemisphere) will probably start bloom during August and finish flowering in late September or early October. Many outdoor growers enjoy the often compact, squat and bushy nature of growing autoflowers outdoors. Autos can be easier to hide than 3-4 metre tall photoperiod monsters!

Autoflowering cannabis seeds also do very well in a greenhouse or polytunnel. As with feminised strains, a greenhouse helps protect your plants from the worst of the late-season weather. It’s something to consider if you have significant concerns about the October weather at your grow location/latitude.

Feminised strains planted in July will have a month (or less) before they show signs of bloom. That means it is more realistic to have modest expectations of the final plant size and yield. But even with a July start, you can still harvest some good quality buds in autumn/fall.

Cooling cannabis plants during summer

How to shade cannabis plants in summer? On the hottest days you may want to keep your plants out of the midday sun, if only for a few hours. Cooling cannabis plants during summer isn’t easy.

If grown in a container, move your plant to a shaded area. Some growers create shade for their plants with a tarpaulin, but this isn’t always easy when growing outdoors.

Avoid placing your plants on a hot tiled surface which can greatly increase temperatures in the root zone. Likewise, avoid black plant containers which will heat up in the sun and cook the root ball.

Even when a cannabis plant is badly dehydrated it can often recover after a few hours of cool conditions and plenty of water. After all, people have been growing cannabis in hot climates successfully for thousands of years.

The real issues happen if your plant is in mid bloom and hits a heatwave. Recovering from heat stress and dehydration is easier in vegetative growth then it is in bloom.

Professional growers do have a few options. Increasing CO2 content, for example in a greenhouse, allows plants to tolerate higher temperatures. Some greenhouse growers with blackout blinds equipped on their greenhouse have an easy way to shade their plants if temperatures reach dangerous levels.

Harvesting cannabis plants seeded in July

If all goes well, and it often does, your cannabis plants started in July will be ready to harvest around October. If the late season weather is poor, you may consider creating some kind of shelter/cover to keep torrential rain off your buds. With a little bit of luck you may see your plants grow steadily and supply you with some bonus winter buds.

See also  Weed And Feed After Seeding

For those growing in reasonable climates, it is also possible to get an early season auto harvest as well as a late season auto harvest. The following grow review from Denmark shows how even Scandinavian growers can get two successive autoflower harvests each year

Grow cannabis from seed to harvest in 3 months!

Even if you have left it late to plant your cannabis seeds this year you can still get a decent harvest with a short 3-4 month summer grow. Feminised seeds, and perhaps especially autoflower seeds, are great options for growing cannabis in summer even with a late start. If you are thinking about a late season outdoor grow remember it’s easy, secured and fast to buy cannabis seeds online!

Harvesting Weed Seeds

Concerns about a growing resistance to herbicides

In Mediterranean or arid climates, particularly in areas with marginal soils, crop rotations are often limited to a narrow range of hay, pasture, a handful of winter legumes, or rainy-season grasses. Arid conditions and weathered soils drove Australia’s rainfed grain growers to adopt no-till strategies earlier than their counterparts in California. While beneficial from a water use perspective, successful no-till systems depend on herbicides to control weeds that were traditionally kept in check with tillage.

Dependence on herbicides alone in these systems has resulted in weeds with resistance to multiple modes of action. In Australia, there is one documented population of rigid ryegrass (Lolium rigidum) that is resistant to 15 different herbicides, covering seven different modes of action. Italian ryegrass (Lolium multiflorum), an annual winter species commonly found in small grain production systems in California is also notorious for its ability to develop resistance to entire groups of herbicides. One population collected in California orchards has resistance to four modes of action[1], but this population is not yet widespread.

One advantage is that California is still a long way from Australia in terms of herbicide resistance in our small grain cropping systems. We can look to Australia for 20 years of methods and data that have arisen in an effort to combat herbicide-resistant weeds. And, if we can find a way to slow the spread of herbicide resistance, we may be able to continue relying on some of the herbicides that are available in our area.

What is Harvest Weed Seed Control?

When growers need to manage herbicide-resistant populations of weeds without tillage, one strategy is to reduce the amount of seed returned to the seedbank by destroying, or removing weed seed caught during harvest operations. Collectively these strategies are referred to as Harvest Weed Seed Control (HWSC). These methods have long been studied in Australia. Researchers at Washington State University[2], Virginia, Texas, and other parts of the US have been looking into these methods for several years. With increasing herbicide resistance developing in Italian ryegrass populations in California, similar approaches may be worth exploring in the Sacramento Valley.

HWSC methods include several different strategies. Each have their own constraints and challenges, and all are designed to physically destroy seeds during or after small grain harvest. This prevents new seeds from entering the seedbank, including those that are from plants partially or fully resistant to herbicides used in the field. This reduces the rate of resistance development and the spread of resistant genes.

Narrow-windrowing – Sorting straw and chaff into narrow windrows, in an effort to contain weed seed in a small area. Windrows can be burned, grazed, or if narrow enough, allowed to compost/ rot in place. If the windrows are left alone, the high rates of carbon will drive soil microbes to scavenge for nitrogen, which subsequently immobilizes plant available nitrogen. Low available nitrogen adds to a crowded, competitive, and less-than-ideal environment for a large number weed individuals that otherwise thrive in high-nitrogen environments. Although this reduces the overall area for the crop, the tradeoff is reduced weed pressure in the rest of the field. This method is improved by the use of controlled-traffic farming, which ensures that the chaff lines end up in the same area after every harvest (maintaining the competitive environment and containing the weed seed). The material in the windrows can also be destroyed with burning or by grazing. Burning in windrows has been shown to greatly reduce the survival rate of Italian ryegrass seeds, while additional studies have shown that other species of ryegrass have a roughly 10% survival rate in ruminant stomachs. However, grazing and burning, particularly in the context of California’s wildfire risks, have their own understandable challenges associated with them.

Chaff lining/ Chaff tramlining – This technique is similar to narrow windrowing, but in this case only the chaff is funneled into a narrow area and straw is spread throughout the field as normal. Chaff can also be moved to the sides of the combine (using a lateral conveyor belt), being deposited under the path of the wheels (this process is referred to as “tramlining”). Controlled traffic farming ensures that the seed is concentrated in the same place every year. In the case of tramlining, tractor wheels run over the weedy areas with every field operation, ensuring that any weed seeds that germinate end up growing in compacted, competitive, and highly-trafficked soil.

Direct Baling – Collecting straw and chaff immediately into bales, usually using a tow-along baler behind the combine. After harvest, bales can be moved off the field, thereby removing a large proportion of weed seed before it can disperse into the soil. However, removal of this much biomass can be problematic for growers with low organic matter soils that otherwise benefit from maintaining residues on the ground.

See also  Seed Weed Salad

One version of an impact mill attachment added to the back of a combine behind the cleaning sieves (photo: Redekop Mfg)

Integrated impact mills – In these systems, chaff is still ejected back into the field, but only after initially going through a hammer mill that shatters and destroys the seed. High initial equipment investments can cool grower enthusiasm. However, one 2017 report from Australia indicated that 29% of growers considered impact mills to be part of their future operations, indicating that at least some growers consider the benefits to outweigh the costs. Combine compatibility can also be a problem as most of the mills are designed to accommodate the larger combines of the midwest, whereas most California combines are typically optimized for relatively smaller acreage.

Limitations and project work

The caveat to all of this is that in order for HWSC to be effective, fields need to be harvested before weed seeds shatter (falling from the plant to the ground). As of yet the shatter patterns of Italian ryegrass in California are not well known. Additionally, previous research has indicated that Italian ryegrass seed retention at small grains harvest can be highly variable across different locations. For example, researchers from the inland Pacific Northwest have reported Italian ryegrass seed retention rates at harvest of 27-50% whereas a 58% of seed retention has been found in Australia. Furthermore, grains in California are planted at different times of the year and our harvest season occurs at different times of the year relative to Australia (not to mention the Pacific Northwest).

Shatter patterns might well be the same as those in other areas of the world but calling for a full scale HWSC revolution isn’t very useful unless we know that a good amount of the weed seed has not yet shattered in the field when small grain crops are harvested.

In an effort to address this, UC researchers will begin collecting data on the shatter status of Italian ryegrass populations in several areas of the Sacramento Valley leading up to harvest. If we consistently see that a significant portion of the Italian ryegrass seed remains attached to the plant at harvest, then HWSC strategies may offer viable control options for California. Conversely, if ryegrass seed has largely shattered by the time our grain crops are harvested, then California growers may need to consider other options for control.

Of course, the best control strategies for herbicide-resistant weeds still include a mixture of different tools such as: the use of herbicides with different modes of action (including pre-emergent and post-emergent types where possible), the use of diversified crop rotations, and well-timed mechanical control. However, a better understanding of the potential for HWSC in California may give growers an edge in reducing the spread of herbicide resistance.

If growers in Sacramento, Solano, or Yolo County are interested in collaborating with UC Cooperative Extension Agronomists in trials focusing on control of Italian ryegrass in small grain crops or have related questions, please reach out to Konrad Mathesius ([email protected]).

[1] : ACCase inhibitors, ALS inhibitors (imazamox, mesosulfuron), PS1 inhibitors (paraquat), and EPSP synthase inhibitors (glyphosate)

[2] My thanks to Dr. Ian Burke and Prof. Drew Lyon of WSU for sharing their research and insight regarding HWSC of Italian Ryegrass and other troublesome weed species.

Seed Shattering: A Trait of Evolutionary Importance in Plants

Seed shattering refers to the natural shedding of seeds when they ripe, a phenomenon typically observed in wild and weedy plant species. The timing and extent of this phenomenon varies considerably among plant species. Seed shattering is primarily a genetically controlled trait; however, it is significantly influenced by environmental conditions, management practices and their interactions, especially in agro-ecosystems. This trait is undesirable in domesticated crops where consistent efforts have been made to minimize it through conventional and molecular breeding approaches. However, this evolutionary trait serves as an important fitness and survival mechanism for most weeds that utilize it to ensure efficient dispersal of their seeds, paving the way for persistent soil seedbank development and sustained future populations. Weeds have continuously evolved variations in seed shattering as an adaptation under changing management regimes. High seed retention is common in many cropping weeds where weed maturity coincides with crop harvest, facilitating seed dispersal through harvesting operations, though some weeds have notoriously high seed shattering before crop harvest. However, high seed retention in some of the most problematic agricultural weed species such as annual ryegrass (Lolium rigidum), wild radish (Raphanus raphanistrum), and weedy amaranths (Amaranthus spp.) provides an opportunity to implement innovative weed management approaches such as harvest weed seed control, which aims at capturing and destroying weed seeds retained at crop harvest. The integration of such management options with other practices is important to avoid the rapid evolution of high seed shattering in target weed species. Advances in genetics and molecular biology have shown promise for reducing seed shattering in important crops, which could be exploited for manipulating seed shattering in weed species. Future research should focus on developing a better understanding of various seed shattering mechanisms in plants in relation to changing climatic and management regimes.

Keywords: crop improvement; harvest weed seed control; seedbank; weed evolutionary adaptation; weed seed dispersal.

Copyright © 2021 Maity, Lamichaney, Joshi, Bajwa, Subramanian, Walsh and Bagavathiannan.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.