Do Weed Seeds Need Light To Germinate

Cover crops differ from ‘regular’ crops in that they are grown solely so the soil is covered, rather than for harvestable things. Cover crops are used by lots of folks – grain farmers, vegetable farmers, flower farmers, and they offer lots of soil benefits, as described in this blog. But they can also help control… The difinitive guide to germinating cannabis marijuana seeds from AmsterdamSeedSupply. Much controversy surrounds the raising of cannabis seed. Many first time growers are bombarded with advice, often conflicting, on how exactly this should be done.

How can you prevent weed seeds from germinating in your garden?

Cover crops differ from ‘regular’ crops in that they are grown solely so the soil is covered, rather than for harvestable things. Cover crops are used by lots of folks – grain farmers, vegetable farmers, flower farmers, and they offer lots of soil benefits, as described in this blog. But they can also help control weeds! Let’s explore how.

First, let’s think about the life of a weed seed. Better yet, let’s pretend we are a weed seed trying to grow in your garden. We’ll start sitting in or on the soil. One of the biggest threats to a seed is something most people don’t normally think about: getting eaten. Mice, crickets, beetles, ants, birds (including chickens) – these things all love to eat the seeds sitting in the soil. Often the seed-eaters are themselves constantly in danger of getting eaten. A cover crop provides protection for seed-eaters. It’s harder for a hawk to see a juicy mouse running along the ground if there’s a cover crop. The mice protected by the cover crop will eat a lot more seeds.

Seed-eaters such as mice can hang out and eat weed seeds under cover crops, safe from predators. Credit: Gina Nichols

Pretend you, the weed seed, didn’t get eaten. It’s time to think about germinating. But you, the weed seed, can only germinate if you get the right ‘cues’. Weed seeds are incredibly smart. A lot of weed seeds will only germinate when they sense ‘pure light’. Light changes as it passes through green leaves. Weeds don’t want competition, so they will wait until there are no other living plants around before they germinate. So, what if you planted a cover crop? The cover crop, alive or dead, is blocking that pure light from hitting the soil, where you and your weed seed friends live. You might never get the cue to germinate.

Another cue seeds look for is large swings in temperature. If the soil gets really warm during the day, then cools back down at night, this is a cue there isn’t anything trying to compete with it. Under a cover crop, the soil is shaded during the warm parts of the day, so the temperature swings are much less drastic. You might sit there waiting for a cue for a long time. But the longer you sit there, the higher the chance you’ll get eaten by one of the seed-eaters.

Let’s say you managed to get all the cues you needed to germinate. Congratulations, you are a weed seedling! But your fight is just beginning. The cover crop is hogging a lot of the things you need – light, water, nutrients – it’s stealing resources. And the cover crop is bigger than you, you’ll most likely just get the ‘leftovers’. The cover crop is making your life hard, so you are not going to flourish. And again, there is the threat of being eaten. Mammals love to eat tender little seedlings, and again they love to hang out under the protection of the cover crop, so your chances of survival aren’t great.

As you can see, using a cover crop can make the life of a garden weed much more difficult. In fact, many community gardens plant cover crops in plots that don’t have an owner, just to prevent weeds from taking over. To recap, cover crops can prevent weeds by:

  • Providing protection for seed-eaters
  • Preventing weed seeds from germinating
  • Competing with weeds for resources

Are you sold? Here are three ways you can start integrating cover crops into your garden.

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1. Fall-planting

A simple way to get started is to plant a winter rye cover crop in the fall (October/November) as you put the garden to bed. Many gardening seed companies offer winter rye seeds. It’s a hardy plant that survives most winters if it gets to be one soda can tall before winter truly sets in. It also puts a satisfying ‘green’ in the garden during months that can feel dreary.

You want fall-planted cover crops to be about one soda can tall before Thanksgiving. Credit: Gina Nichols

2. Spring-planting

If you are reading this in December, you might think you’ve missed your cover-cropping chance. You’re wrong! You can plant an early-season cover crop such as oats and hairy vetch as early as March. Good garden areas for these include places destined for crops you’ll transplant in the summer (pumpkins, eggplants, tomatoes), or pathways you want to keep from getting weedy.

3. Summer-planting

If it gets to summer and you find you have some empty space, buckwheat is an excellent summer cover crop. It grows quickly, bees love the flowers, and is easy to kill by mowing or pulling.

For all cover crops, you need to make sure the cover crop is dead before you plant your harvesting crop. Some cover crops will die if you mow them, but others need to be pulled (you can place the pulled plants back on the ground to keep it covered), crimped (imagine stomping on the plants to break their stems), or tilled. If the cover crop is still alive, it will compete with the main crop for nutrients and light, which you don’t want.

A happy garden area goes into the winter covered by a winter rye cover crop at Mustard Seed Community Farm in Ames Iowa. Credit: Gina Nichols

Some other common cover crops are clovers, peas, tillage radish, mustards, barley, wheat, and Sudan grass. Many gardening companies also offer seed mixes. Once you start using cover crops you might find they are just as exciting as the food-producing plants in your garden. As a rule of thumb if you see bare soil you might have an opportunity to use a cover crop, the quiet weed fighter. Happy cover cropping!

Answered by Gina Nichols, Iowa State University

This blog is part of Crop Science Society of America’s Seed Week celebration. Why celebrate seeds? Anyone who plants a seed is investing in hope. That’s one of the attractions of seeds. For the gardener, it could be hope for a beautiful flower, or perhaps a delicious zucchini squash. For our farmers, seeds are the hope of this year’s yields of produce, cash crops or forage. No matter the size or shape of the seed, they all can bring forth new life. At Crop Science Society of America, we hold seeds in very high regard. Please visit our Seed Week webpage for news stories, blogs and more information about seed research and facts.

Please visit our Seed Week webpage for more information.

Read the other blogs in our seed series!

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.

Germinating Cannabis Marijuana Seeds

Much controversy surrounds the raising of cannabis seed. Many first time growers are bombarded with advice, often conflicting, on how exactly this should be done; however, it need not be such a complicated task. Cannabis seed is simple to grow, and if fresh, 90-100% germination rates are not unusual.

The ‘Kiwiland Method’ for raising seed, has been developed from professional horticultural practices used the world over. We use it because it works, and it’s simple.

Table of contents

Needed equipment

The list below is standard equipment recommended by Kiwiseeds and assumes you already have the necessary grow space and lighting set up. If you haven’t already got your equipment you can buy that online at https://www.kiwiland.com/

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1. Propagator with bottom heat or
2. Heat pad + seed-tray
3. Thermostat controller
4. Soil thermometer
5. Perlite

6. Large jiffy pots + seed-raising mix or
7. Rockwool starter blocks
8. Fine sprayer
9. Identification labels

Perlite preparation

Wet thoroughly enough perlite to cover the bottom
of the propagator approximately 2cm deep. Plug the propagator, or heat pad, into the thermostat controller, plug the controller into the power and set for 23 C. Place the heat-sensing probe into the wet perlite just beneath where the seedlings roots will be. If using a heating pad lay it out beneath the propagator tray.

Jiffy pots preparation

Pre-soak the jiffy pots in warm water then fill them to the top with seed-raising mix making sure to take out any bigger pieces that may obstruct the young shoot as it emerges.

(This can also be done with the help of a coarse sieve if you like.)

Completely saturate the jiffy-pots and their contents, but allow them to drain well. Do this carefully so as not to wash the fine soil away. Top them up and repeat if the mix has sunken too much. It’s important to have them as full as possible to give the young roots plenty of room to grow for the week or two until they are potted on, and, because having a greater volume of the mix in the pots means they take longer to dry out under the warm lamp.

With a thin pointed object such as a pencil, make a small hole in the center of each jiffy-pot about twice the depth that the seed is long (This varies with strain, but 5-8mm deep should be sufficient. Often the mistake is made of planting seeds too deeply, and they rot before they see the light of day. To ensure this doesn’t happen, never sow seeds deeper than 1cm). If sowing more than one variety remember to prepare identification labels in advance and label them as you go to prevent mix-ups.

Put the cannabis seeds in Jiffy pots

Sow seeds directly into the holes, and cover with a little of the moist seed-raising mix from around it with the help of the pencil. Use a little more fine mix if needed. Some growers have the patience to sow seeds a certain way up, and this can be beneficial, especially with big seeds. If this is done place the seed, point up, ensuring the root can travel downwards with ease.

Watering the seeds

Using the mister bottle, spray the freshly covered seeds until the mix is damp. Don’t pour water onto the pots as this can wash away the mix and expose seeds.

Transfer jiffy-pots into pre-warmed propagator tray, and settle them in making sure the wet perlite surrounds the pots, getting right up between them. This ensures the pots stay moist until well after the seeds germinate, protecting the young roots from drying out.

Lighting, temperature & humidity

Set the tray under either fluorescent lighting or a low-wattage H.P.S. to keep the newly planted seeds warm. At this stage no light is necessary but warmth is important, and low light provides this without drying the pots out. An air temp of 20-22C is ideal, a degree or two lower than the soil temp (around 23C). Humidity if regulated can be set for around 60%.

Growing the cannabis seedlings

As soon as the seedlings have germinated they need light. The food store supplied by the seed itself has all but been used up, and the plant needs light to photosynthesize and grow.

When growing marijuana in the vegetative stage you may choose how long you wish to keep the lights on, as long as it’s 18 hours or more. The advantages are that plants will grow faster with 24 hours light, and a constant temperature is easier to maintain this way, something hugely beneficial to young seedlings. Disadvantages are that you’ll need to water more, of course, your lamps and ballasts don’t get a break, and the electricity bill increases.

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Some people advise keeping young seedlings under fluorescent lighting for a while but this doesn’t provide them with the correct spectrum for photosynthesis. It is best in our opinion to place seedlings directly under low wattage H.P.S lamps, 150/250/ or 400 watts, at a good distance away.
Once the plants are a few days growing they need to be moved closer to the lamps in order to prevent stretching. Move them as close to the lamp as the tops of many plants would be comfortable. (30-60cm depending on the lamp size.)

Make sure a breeze (oscillating fan) is blowing over the young plants, primarily so they don’t overheat, but furthermore to help strengthen delicate stems by stimulating cellulose production. Spindly stems cannot support heavy flowering growth. The importance of your internal air circulation cannot be stressed enough. It will exercise your plants and make them grow stronger while reducing many hazards that could ruin your crop.

Now that the plants have strong light they require more water and nutrients as well. A light organic feed or nutrient solution starting with an E.C of no more than .8 (with the water already at .5) can be sprayed directly on the plant and watered into the soil. The seed-raising mix contains no nutrients so within a few days the plants will be hungry.

Young seedlings love humidity, and a constant 60-70% is ideal at this stage. Use a cheap mister bottle, and spray regularly freshwater (ph- 6.5-7.5) over the leaves. This increases humidity, and washes dirt and dust off the leaf surface, unclogging stomata and enabling the plant to breathe properly. In natural conditions, the rain would do this for us.

Problems raising seedlings

Problems can occur during germination. Here is a list of some of the more common reasons why your seeds may not be doing so well.

Too wet
Seeds need to be damp, not wet for germination. Excess water prevents oxygen from getting to the seed. Poorly drained soils may also cause soil fungus diseases. The condition of wet soils may be improved by adding perlite, which will aerate your soil. Make sure any trays or pots you use have holes in the bottom to let the excess water drain.

Too dry
A certain amount of water is essential for germination, so maintaining constant soil moisture during the germination period is vital. Spray the soil surface with a fine mist, or cover containers with glass or a damp cloth to prevent your soil drying out. Make sure you remove the cloth once the shoot emerges.

Too hot
High temperatures result in excessive soil desiccation and injury to seeds and seedlings. We recommend a constant temp of 20-25 degrees.

Too cold
Cold temperatures can kill seedlings and prevent germination. Cool temperatures can result in slow, uneven germination, and attack by soil diseases. If growing outside, you may want to start your seeds indoors, before outdoor planting. Make sure planting is not done too early when there is still a chance of frost.

Too shallow
If you sow your seeds too shallowly the seeds can dry out. A depth of between .5 to 1cm is about right.

Soil too firm
Making your soil mix too firm can prevent oxygen from getting to your seeds and drainage can be affected. Pat freshly covered seeds lightly with your fingers.

Soil too loose
Soil that’s too loose results in too much air surrounding the seed. Seeds planted in this manner will not absorb moisture properly, and it’s likely they’ll dry out. Cover freshly sown seeds with fine mix and pat down lightly with your fingers.

Soil fungus
Seeds may rot, or the young seedlings may fall over. Overwatering, poor drainage and lack of aeration will increase the likelihood of this occurring. Plant seeds in sterilized potting mix, and make sure your containers are clean.

Non-viable seed
If your seeds have not been stored correctly they can deteriorate. Look for darker seeds that are a little bigger, without cracks or chips. Any seeds that look shriveled or wrinkled should be discarded, as this means the seed has dehydrated and is dead.