Mulch for Weed Control and Soil Health
Mulch provides several benefits to the garden. Luckily, adding mulch is one of the easiest gardening tasks you can undertake. The question isn’t whether you should use it or not (the answer to that is a resounding yes!) The question is, which type of mulch should you choose, and how should you apply it?
Benefits of Mulch
- Mulch is a great weed suppressant. A nice, thick layer of mulch inhibits weeds in two important ways. First, by thoroughly covering the soil and depriving weed seeds of the light they need to germinate, mulch prevents them from gaining a foothold in the first place. Secondly, bare dirt is the perfect place for weed seeds to land and germinate. By covering all of your bare soil with mulch, most weeds will never be able to come into contact with the soil.
- Mulch helps retain soil moisture. Maintaining a consistent level of moisture in your soil is a big part of growing healthy plants. A plant that has a constant level of adequate moisture is less likely to become stressed, which means that it will be better able to resist insects and diseases. In tandem with keeping the soil moist, mulch also keeps the soil cooler in hot weather, which will prolong the amount of time it takes for many plants to bolt or go dormant. Some plants bloom best in cooler conditions, and mulch will aid in keeping these plants blooming longer.
- Mulch feeds the soil. Organic mulches (as opposed to inorganic ones such as glass, plastic, or rubber) will break down over time, adding nutrients and organic matter to your soil. The worms and microbes in the soil will break down organic mulches, which will result in healthier soil life.
Popular Types of Mulch
The following mulches are all organic, so they will nourish your soil while suppressing weeds and maintaining soil moisture. Each type has its strengths and weaknesses and will work better in some situations than in others.
Shredded or chipped bark doesn’t break down as readily, which means that it won’t provide as much nutrition to your soil, but also doesn’t need to be replenished as often. Some popular woods for mulch are cedar, pine, and cypress. Bark mulches work well in many settings but are especially useful around trees and shrubs and on pathways.
Chopped leaves are plentiful and free if you have enough trees. They can be shredded by running over them a couple of times with a lawnmower or running them through a chipper/shredder. They work well on perennial beds, in vegetable gardens, and mixed borders. They break down fairly quickly and provide plenty of nutrition to the soil.
Straw is a popular choice for vegetable gardens as well as informal paths. It has a very utilitarian look, so it probably wouldn’t work in perennial borders or foundation plantings. It breaks down fairly quickly.
Grass clippings are another plentiful, free mulch. The only caveat here is to make sure that the grass clippings haven’t been treated with chemicals—you don’t want to introduce pesticides and herbicides into your organic gardens. They tend to break down very quickly, and, because they break down so fast, can heat up the soil rather than cooling it down. Grass clippings work well in vegetable gardens, informal mixed borders, or under a more attractive mulch, such as shredded bark or cocoa hulls.
Cocoa hulls are the most expensive of the popular mulches, but the look it provides for your garden is well worth it. Cocoa hulls have a dark brown, Earth-like appearance, so you don’t even notice the mulch. However, they tend to develop mold in humid, wet weather. This mold doesn’t harm your plants or soil, but it is unsightly.
Pine needles are another informal, and possibly free, mulch material. They look great in gardens of all kinds.
Pine needles can be a bit acidic, so it’s best to avoid using them near plants that don’t tolerate acid soils very well.
Compost (including leaf mold), like cocoa hulls, just fades into the plantings, so you don’t even notice that it’s there. Besides looking great, it provides plenty of nutrients to your soil and increases microbial activity. It will need to be replenished fairly often (at least once a year) but if you have your compost pile, you’ll have a steady supply of black gold ready to use.
How to Apply Mulch
There is a right way and a wrong way to apply mulch. The biggest mistake people make when adding mulch is that they don’t apply enough. To smother weeds and retain soil moisture, a 2 to 3-inch layer of mulch is necessary. Less than 2 inches of mulch will let enough light through to allow weed seeds to germinate.
In addition to applying the right amount of mulch, you also need to make sure that it isn’t pushed against your plants. Pull the mulch back from tree trunks, shrubs, and the crowns of your annuals, perennials, and vegetables. Give your plants an inch or so of space. When mulch is applied up to a plant, it can hold moisture and cause the plant to rot.
Organic mulches, because they break down and improve your soil, need to be replenished from time to time. Plan on adding an inch of mulch to your gardens every year, either in spring or fall.
A layer of mulch can benefit every single area of your garden. Whether you have a ready-made supply, such as grass clippings or leaves, or whether you choose to order some in bulk or buy it in bags at your local garden center, the important thing is to make sure you use it. Your plants and your soil will appreciate it.
Mulch not only makes the garden look neat and tidy, but it suppresses weeds, maintains soil moisture, and adds nutrients to the soil as well.
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.
Share this story
- Share this on Facebook
- Share this on Twitter
Share All sharing options for: How to Prevent Weeds From Growing
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
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.