By Fern Campbell
Piedmont Master Gardener
Do weeds tend to take over in your vegetable garden? You’re not alone. More time is spent on trying to control weeds than any other home gardening activity, especially if you let the weeds get a head start. If left unattended, weeds will compete with your vegetable plants for water and nutrients, and they can harbor insect pests and diseases.
This year, get a jump on the weeds by mulching your garden. Leave no soil surface bare.
How It Works
Simply put, a garden mulch is any material—organic or inorganic—spread on the soil surface to modify the environment where the plant is growing. Thorough mulching reduces the amount of light that reaches the soil surface, which prevents or slows the germination of weed seeds. Mulching can drastically cut the time you spend on weeding while helping your garden in many other ways. These include:
Reducing evaporation of soil moisture, thus maintaining more uniform moisture conditions;
Reducing soil erosion and crusting caused by the impact of heavy rainfall;
Adding nutrients and humus as organic mulch material decomposes, which helps to maintain soil tilth, keeping the soil open and loose for water and air penetration; and
Decreasing soil splashing on plant leaves, which will slow the development of soil-borne diseases and keep the fruits cleaner during heavy downpours.
Mulching also helps regulate soil temperatures. Plastic mulches will warm the soil earlier in the spring, increasing plant development. Organic mulches act as insulation, helping to cool the soil in the heat of summer.
Organic mulches should be applied after your crop has begun to grow and after the soil is warmed, but don’t wait too long if you want to prevent weed seeds from germinating. Weed the area well before mulching, and apply when there is reasonably good soil moisture and before the weather turns hot. Water well unless there’s a good soaking rainfall in the forecast.
Straw vs. Hay
You can choose from a wide variety of organic mulching materials that are readily available for the vegetable gardener, including straw and hay. What’s the difference? This is a frequently asked question, as folks tend to “intertwine” the two names loosely. They’ll say, “We’re going on a hayride,” when in fact they’ll be sitting on bales of straw, not hay, which is pricklier and more irritating.
Straw bales are the leftover hollow stalks of harvested grain plants, most commonly wheat but also barley and oats. Straw is fluffier than hay, and its bales can be easily broken apart and used for many things, such as animal bedding, cover for freshly planted grass seeds or mulch for your vegetable garden.
Hay, by contrast, is made up of grasses— Timothy, orchard grass, rye grass, broom grasses—and often mixed with the alfalfa legume. Think of hay as feed for any animal that grazes a field. Hay is cut and gathered into large round or square bales while the plants are still green and moist. Thus the bales are heavier and tighter, making hay more difficult to “fluff” and spread on the garden and more prone to mold or mildew. Yes, if the hay is free of weed seed and brambles, it could be used in your garden, but the reality is that most hayfields are full of weeds. There’s also the worry that the farmer may have used a persistent herbicide in the field, which could harm your plants. (For more on this issue, search online for Virginia Cooperative Publication PPWS-77P, “Plant Injury From Herbicide Residue.”)
Straw is clearly the better choice as a vegetable garden mulch. Its bales are much lighter, easier to handle and can be purchased at farmers’ co-ops and some big-box stores. It should be spread six to eight inches thick. Although weeds from straw are less of an issue, sometimes leftover wheat seeds will sprout in your garden. Just pull up the sprouts and lay them on top of the straw mulch.
Other Organic Mulch Materials
Other organic mulch options for the vegetable garden include:
Living “green” mulch—By using intensive gardening methods, you can plant densely enough so that your crops shade the soil and thus will help control weeds. This will reduce the need to add other organic material, but it also requires succession planning. For a season-to-season planting guide for intensive gardening, search online for Virginia Cooperative Extension Publication 426-335.
Fall Leaves—This is an attractive and easy-to-obtain choice for the vegetable garden. Ideally, you should coarsely chop or shred the leaves before using, and you can mix them with other material such as compost. Apply three to four inches of leaves to provide good annual weed control. Leaves will decompose within the year and will improve the soil as they break down.
Pine needles—Baled pine straw can be found in garden centers and is a desirable choice for areas where a long-lasting mulch is needed. It breaks down slowly and does not compact. Use it around perennial fruits and vegetables such as blueberries and asparagus beds, and of course, around trees and shrubs.
Compost—This is an excellent source of nutrients and should be applied two to four inches thick around your plants. When using compost as a “top dressing” mulch, it is best to obtain the compost from commercial producers that can heat it up to 130–160 degrees, which will kill weed seeds.
Sawdust—This is a relatively inexpensive material available from sawmills. Use aged sawdust in the vegetable garden rather than fresh sawdust, which contains a great deal of carbon and requires nitrogen to break down. This can result in nitrogen deficiency for your plants if you do not add extra nitrogen—a half-pound of actual nitrogen per 10 cubic feet of sawdust is needed. Fresh sawdust also tends to form a crust that makes the surface less permeable to water. Fresh sawdust is a better option for your pathways. Apply two to three inches thick.
Shredded Hardwood—A two- to three–inch layer provides good weed control, but extra nitrogen is also needed as it breaks down. This is another great choice for pathways.
Grass clippings—Depending on your setting, grass clippings free of weeds can be used in your garden, although we recommend mulching grass clippings back into the lawn. Allow the clippings to dry before placing them in the garden, as wet clippings can mat down and form a smelly (anerobic) pile of rotten material. Avoid using grass from a lawn where herbicides have been applied.
Paper—Two to six layers of newspaper (not the glossy sheets) will work as a weed suppressor but must be held down by some other organic matter, such as straw or leaves. Several gardening supply companies manufacture mulch made of recycled paper, sold as rolls and installed much like plastic mulch. The material breaks down within one season.
Summer cover crops—Fast-growing summer cover crops will fill gaps in your garden from spring to early fall. They suppress weed growth while also controlling runoff and erosion, as well as adding organic matter to the soil. Buckwheat establishes in 35-plus days from seed to bloom and attracts pollinators and beneficial insects. It is easy to interplant and use in small spaces. Soybeans, cowpeas, sorghum-Sudan grass and Japanese millet are additional options for fast-growing, frost-tender summer crops, depending on the size of your empty beds or space.
Whichever option you choose, be prepared to replenish the mulch as it breaks down and helps build healthy soil. Remember, nature abhors bare ground, and so should you. (The exception is to leave a few bare spots for those ground-nesting native bees.) Follow these mulching principles, and you’ll be amazed at how the weed problems recede and at the improved health of your plants and soil. Enjoy your harvest!
