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… Whether you are planting a winter or upcoming spring crop, re-seeding or enhancing a stand of Conservation Reserve Program (CRP) or State Acres for Wildlife Enhancement (SAFE), or simply interested in seeing if a winter,…
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.
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
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.
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.
Is Your Seed Dead or Alive – A Seed Viability Test
Whether you are planting a winter or upcoming spring crop, re-seeding or enhancing a stand of Conservation Reserve Program (CRP) or State Acres for Wildlife Enhancement (SAFE), or simply interested in seeing if a winter, spring or possible summer cover crop planting will help the overall health of your soil, it is important to make sure the seed you plan to use is viable.
A “Seed Tag” usually accompanies seed purchased from seed companies. This tag tells the buyer several things: 1) what variety and species is in the bag, 2) a lot number which tracks where the seed was produced, and 3) information such as the percent purity, percent inert material, percent weed seed, percent noxious weed seed and percent total germination.
Unfortunately, not all seed comes with a tag. Any seed that has been set aside from harvest to be planted for next year’s crop will not have this information. One- or two-year-old seed should be fine to plant, but what if a producer had some seed from 10+ years ago that they wanted to use?
Fortunately, there is a simple way to test seed viability.
You will need:
- A petri dish (plastic, shallow, flat, clear dish) or a ziplock bag
- A lid for the petri dish
- A paper towel
- Plastic wrap
Then, you’ll follow these five simple steps:
- Moisten a piece of paper towel with water and place it in the petri dish;
- Evenly place 10 or more seeds on the paper towel. You may want to fold the towel over the seeds so both sides of the seeds are moist;
- Place the lid on the dish and wrap tightly with plastic wrap;
- Place in a warm environment (i.e., kitchen counter); and
- Wait for 7 to 10 days, then check the dish for seeds that have visibly germinated (i.e., sprouted) and count them.
The percentage of germinating seed also known as pure live seed (PLS) will give you a fairly good idea how that same seed should perform when planted provided the seed receives adequate moisture. Adjust seeding rates based on the percentage of germinating the seed.
Species: Eltan WW
Desired seeding rate: 12 seeds/ft row or 50 lbs. /A on 12-inch spacing (St. Andrews Variety Trial Seeding Rate)
The seeding rate of bulk seed: 50/0.80 = 55.5 pounds of bulk seed
Therefore, you will need an additional 5.5 lbs/acre of seed to reach either the desired 12 seeds/ft row or 50 lbs/acre based on a PLS of 80%.
For help with converting lbs/acre to seeds/ft row, lbs/acre to seeds/acre or vice versa for both, please visit our Crop Tools & Calculators page and check out the Seeding Rate Converter calculator.
For questions or comments, contact Dale Whaley by email at [email protected] or by phone at 509-745-8531.