How To Prevent Weed Seeds From Germinating

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Here’s how to keep weeds out of garden, mulch over weeds, use landscaping fabric, and 6 prevention mistakes to avoid for better garden weed control. Listed in this article are 5 effective ways to minimize weed growth in your garden / turf / landscape with Mirimichi Green. 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…

How to Prevent Weeds From Growing

Tips on how to keep weeds out of the garden, add the right amount of mulch over weeds, and 6 mistakes to avoid to keep your garden weed-free.

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Think it’s an overstatement to call it the war against weeds? Here’s what you’re up against.

A single redroot pigweed is able to produce up to 30,000 seeds in a season. And those seeds can remain alive in the soil for 70 years waiting to sprout and overrun your perennial border at any time.

Controlling weeds is a fight you can’t win entirely because they always grow back. But you can keep weeds under control by depriving new ones of the conditions they need to take root in the first place. Let’s look at how to prevent weeds from growing.

(For those of you who already have weeds attacking your yard, read our article on How to Get Rid of Weeds.)

Weed Prevention

As with most types of prevention, discouraging weed seeds from sprouting requires some extra time now so you can save a lot of time later.

Spread Landscape fabric and cut it to fit around plants. Photo by Saxon Holt

Fertilize Enough, but Not Too Much

Too little fertilizer can lead to sparse lawn that loses the competition with weeds. Too much helps nurture certain weeds, notably annual bluegrass, Bermuda grass and crabgrass. Strike a balance by following the application rates on the package. And use a fertilizer with a high percentage of controlled-release nitrogen, such as sulfur-coated urea, ureaform or IBDU. These provide a slow, steady nutrient supply.

The frequency and timing of your fertilizing efforts are also crucial to healthy lawns. Both vary depending on your lawn type and the length of your growing season. Most northern lawns need only one or two applications of fertilizer annually—once in fall and sometimes a second time in spring. Southern grasses might require three feedings—early to mid-spring just after the grass greens up, early summer and again in early fall.

Water Grass Infrequently and Deeply

Frequent, light watering causes shallow roots and helps annual bluegrass, crabgrass, chickweed, sedges and other weed seeds germinate. If you water too little, the lawn suffers while spotted spurge, Bermuda grass, quackgrass and other weeds adapted to drier soil thrive. Instead, provide your lawn with infrequent, deep soakings. Lawns need about 1 inch of water per week. Set an empty tuna can on the lawn to determine when you have applied 1 inch of water.

Can I Put Landscape Fabric Over Weeds?

Yes, you can. Synthetic landscape fabrics provide a physical barrier to weeds yet allow air, water and nutrients through to plant roots. Spread the fabric over bare soil around trees and shrubs; overlap several inches of fabric at the seams. Anchor the material with U-shaped metal pins, then conceal it with 1 to 2 in. of mulch, such as stone or bark chips.

You can also use landscape fabrics to control weeds under decks and in pathways (spread over the excavated soil base before you add gravel or sand). A 3×50-ft. roll of landscape fabric, such as the Typar shown below, costs about $10. The fabric is also available in 36-in. die-cut circles (about $3 each) for installing at the base of trees.

Photo by Saxon Holt

Smother Weeds with Mulch

Left unattended, weeds will quickly fill in unplanted areas and any open ground around plants. Mulch spread over the soil surface blocks the sunlight most annual weeds need to take hold. Weeds that do sprout are easy to pull because soil beneath mulch remains loose and moist. Coarse chipped or shredded bark is a good choice for large areas between trees and shrubs because it decomposes slowly and doesn’t easily blow away. For paths, a thick layer of sawdust provides good weed suppression because it depletes nitrogen in the soil.

How to Mulch Over Weeds
  1. After clearing a landscaped area of visible weeds, put down coarse-textured mulch up to 4 in. deep.
  2. Apply a fine-textured mulch that packs tightly, such as shredded leaves, to a depth no greater than 2 to 3 in.
  3. Keep the mulch a few inches away from the trunks and stems of plants to prevent disease problems.

Apply Preemergence Herbicides

Preemergence herbicides, such as those containing oryzalin or trifluralin (look on the label for these chemicals), or nontoxic corn gluten meal, kill weeds just as they germinate and will not eradicate established weeds. For a preemergence herbicide to be effective, you must apply it to soil cleared of visible weeds; also, you have to water most of these herbicides into the soil.

Check the label to determine if it is safe for use around the kinds of landscape plants you have and effective against the weeds normally present.

Deprive Weeds of Water

Weeds can’t survive without moisture. In areas with little or no summer rain, drip irrigation or soaker hoses help prevent weed seeds from sprouting by depriving them of water. These systems deliver water to the root zone of plants at the soil level. The soil surface and area surrounding the plants stays relatively dry. In contrast, overhead sprinkler systems spray water over the entire soil surface and supply both garden plants and weeds with water.

You can get in-depth information on drip irrigation from the Irrigation and Green Industry Network in the “Where to Find It” section.

Mow Higher

Mowing too low weakens turf by reducing the ability of a grass leaf to produce enough nutrients. It also lets light hit the soil surface, which helps crabgrass and goosegrass seeds sprout and grow. Check with your local extension service for the recommended range of mowing heights for your grass type. Then mow at the highest level—usually between 2 and 4 inches.

Any weeds that grow through mulch are easy to pull because the soil remains loose. Photo by Saxon Holt

6 Weeding Mistakes

In the process of trying to eliminate weeds, people often make mistakes that lead to more weeds. Here are the most common:

  1. Leaving weeds that are in flower on the ground. Even after they are pulled, weeds like chickweed and purslane can continue to develop seeds.
  2. Piling too much mulch over landscape fabric. As the mulch breaks down, it provides a perfect medium for weed growth from wind-borne seeds. You can actually have weeds rooted to the fabric. Limit mulch depth to 1 or 2 in. over landscape fabric.
  3. Applying mulch containing weed seeds. Sometimes mulches such as straw and wood chips contain weed seeds. To avoid this problem, buy from a reputable nursery that offers mulch free of weed seeds.
  4. Tossing weeds with seeds into the compost pile. A good compost pile can get hot enough (160°F) to kill weed seeds. But there are often cool spots where the seeds can survive. Those that do will be spread in your garden with the compost.
  5. Breaking apart the roots of perennial weeds as you try and dig them out. Each piece can grow into a new plant.
  6. Planting weeds along with your new shrubs and trees. Just a few nutsedge or Bermuda grass plants growing in a nursery container can spread and multiply in your garden. Make sure to remove them before planting.

This Preemergence herbicide, made from corn gluten, is nontoxic. You can safely use it near all of your vegetables as well as around ornamental plants. Photo by Saxon Holt

Where to Find It

Lee Valley Tools Ltd.
Box 1780
Ogdensburg, NY 13669-6780
800/871-8158
Telescoping Crack Weeder

True Temper Hardware
Box 8859
Camp Hill, PA 17011
800/393-1846
Scuffle hoe

Drip irrigation information and supplies:

Irrigation & Green Industry Network
916C N. Formosa Ave.
Los Angeles, CA 90046
www.igin.com
323/878-0318

Raindrip Inc.
2250 Agate Ct.
Simi Valley, CA 93065
www.raindrip.com
877/237-3747
Request the free “Drip Watering Made Easy” guide.

Denman & Co.
401 W. Chapman Ave.
Orange, CA 92866
714/639-8106
Ball weeder

Primus
Box 186
Cherry Valley, IL 61016
815/332-5504
Weed flamer

5 Ways To Minimize Your Weed Growth

There are always weed seeds that lie dormant in the soil. The seeds are waiting for the sunshine to start to germinate or be awoken from a long slumber. To avoid awakening the weed seeds, don’t disturb the soil. Disturbing the soil includes tilling and cultivating. But that seems somewhat impossible when trying to plant new flowers, plants or grass. When planting flowers or plants, sow the seeds above the ground in a small mound of topsoil or compost.

2. Fight the weeds before they sprout

An effective way to prevent weeds is by using a pre-emergent herbicide that will stop weed seeds from ever germinating but won’t kill existing plants and grasses.

The tricky part is determining when to apply a pre-emergent because it must be applied before the weed seeds have time to germinate underground. The best way to know when to apply a pre-emergent is to make note of the date when you see the first weeds in the yard or garden. Then, mark your calendar 3 weeks before that date for next spring and apply the pre-emergent then.

You can also start from scratch by using a non-selective herbicide. This will kill whatever it sprays. It is also recommended to use organic options to prevent harmful synthetic build up in the soil. A great option is Mirimichi Green Weed Control. It is organic, OMRI listed and will show results in 24 hours.

3. Promote healthy plants & grass

If there is healthy grass, weeds will have less room to grow in the lawn. To promote a healthy lawn, reseed bald patches and fertilize if a soil suffers from nutrient deficiencies. By maintaining a healthy lawn, fewer weeds will arise. Nutri-Turf has the ideal balance of nutrients for all grass types and will keep the lawn lush.

4. Keep your plants close

Planting closely together will provide more shade to the soil below, which will prevent weed seeds from getting sunlight and allow less room for weeds to grow. You can usually reduce the recommended planting space on the packaging by about 25 percent. However, most spacing recommendations are based on the prediction that adjoining plants will not touch at their mature size, so follow the guidelines if you are planting plants that are prone to foliar diseases.

5. Create an organic barrier

Spreading an organic barrier around plants will submerge weed seeds and prevent light from starting germination all while keeping your plants cool. Organic barriers are best such as mulches. Mulches can host crickets and carabid beetles, which will feed on weed seeds. To create the organic barrier, spread mulch 2 to 4 inches deep around your plant bed.

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.

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.

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