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.)
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
- After clearing a landscaped area of visible weeds, put down coarse-textured mulch up to 4 in. deep.
- Apply a fine-textured mulch that packs tightly, such as shredded leaves, to a depth no greater than 2 to 3 in.
- 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.
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:
- Leaving weeds that are in flower on the ground. Even after they are pulled, weeds like chickweed and purslane can continue to develop seeds.
- 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.
- 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.
- 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.
- Breaking apart the roots of perennial weeds as you try and dig them out. Each piece can grow into a new plant.
- 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.
Ogdensburg, NY 13669-6780
Telescoping Crack Weeder
True Temper Hardware
Camp Hill, PA 17011
Drip irrigation information and supplies:
Irrigation & Green Industry Network
916C N. Formosa Ave.
Los Angeles, CA 90046
2250 Agate Ct.
Simi Valley, CA 93065
Request the free “Drip Watering Made Easy” guide.
Denman & Co.
401 W. Chapman Ave.
Orange, CA 92866
Cherry Valley, IL 61016
Prevent Weeds in the First Place – You Can Do It!
It may seem like it’s impossible to prevent the spread of weeds – like they have their own magical powers that we can’t suppress – but the easiest weed to manage/control is one that is not yet on your land. Some weeds even invade undisturbed land so even if your land is pristine you should take good precautionary measures to keep weeds from getting established.
Some of our worst weedy offenders spread via their roots, but all weeds can spread by seed — in our socks and shoes, on our dogs or farm animals, hitching a ride on our cars and bikes, etc. Who has never pulled a cheatgrass seed head out of their sock? Heeding these tips as much as you are able will go a long way to preventing the spread of weeds:
- Class A, B & C Weeds
- The Weed Control Toolbox
- Weed Terminology
- Prevent Weeds in the First Place – You Can Do It!
- Additional Weed Control Resources
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Scientific Name: Tribulus terrestris
Puncturevine is an annual weed that sprouts and grows from seed every year and then dies. Starting from the central sprouting point at the root, stems spread out radially, staying low to the ground when the plant has direct sunlight. Dense mats can form with leaf-covered stems trailing out like runners, except the plant does not send roots from these stems. Mats start small and can grow quite large to several feet in diameter. In the shade, the same thing happens but the stems can grow slightly upright instead of flat to the ground.
Scientific Name: Sisymbrium altissimum
Tumble mustard is widespread across the Methow, mostly in open, disturbed (or burned) sites such as roadside ditches, residential areas in the shrub-steppe, ranch and Ag land, and post-fire areas.
Scientific Name: Bromus tectorum
Cheatgrass is probably the most common plant in the Columbia Basin, and it’s one of the most widespread invasive (non-native) grasses in North America.
Scientific Name: Centaurea diffusa
Diffuse knapweed is a biennial thistle that can mature and flower at a wide variety of heights – anywhere from a few inches to a few feet tall.
Scientific Name:Linaria dalmatica
Don’t be fooled by this attractive yellow snapdragon-type flower!
Scientific Name:Salsola kali (also Salsola tragus and Salsola iberica)
Russian thistle is least noticed when it is young – slender, green and soft – and most noticed when it’s a large, spiny, brown tumbleweed.
Scientific Name: Gypsophila paniculata
Baby’s breath is an easily recognizable addition to the Methow Valley’s list of weedy plant species.
Scientific Name: Cardaria draba
Whitetop is a perennial, which in this case is continually expanding downward and outward.
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