Black plastic mulch, first introduced in the 1950s, is a useful addition to your garden. This tool helps increase plant production, reduces the time to harvest for many plants and acts as a useful form of weed control. This material is applied to garden rows in the form of sheets. Then, seeds or seedlings are planted in holes in the sheets, allowing only enough space for desirable plants to grow. Used correctly, black plastic sheets can help you have a healthy, low-maintenance garden.
Black plastic sheeting helps reduce moisture loss from the soil, since it blocks evaporation. It also keeps weed seeds from getting the light they need to grow, so you don't need to hand weed or apply herbicides. This mulch warms the soil in early spring, allowing warm-season crops to grow more quickly and encouraging plants to mature faster. It also reduces the amount of cultivation and hoeing required, both to remove weeds and keep soil in proper condition. That means less chance of root injury and healthier plants.
Using black plastic sheets to kill weeds in your garden can cause your plants to need more water. While this material reduces the amount of water that evaporates from the ground, it increases water loss through transpiration. According to Michigan State University, this problem is most common in lighter soils with good drainage. Black plastic mulch may trap water in the soil in wet areas, encouraging fungal growth and damaging plants. Because this material is non-biodegradable, it can persist in the landscape for years after use, causing an environmental nuisance. Black plastic sheeting is also more expensive than many other types of mulch.
This type of mulch works best on crops grown in hills or at least a few inches apart. These crops include strawberries, many types of beans, peppers, tomatoes, eggplant and squash. Melons also grow well on black plastic sheeting. Crops such as lettuce and spinach don't get much benefit from the mulch, since they are seeded very close together.
Not all black plastic works equally well as mulch. According to Oklahoma State University, gardeners should use 1 ¼ mil embossed plastic, which is more resistant to cracking and wind fatigue than mulches with a smooth surface. Plastic sheeting comes in several widths, from 36 to 60 inches. Choose mulch width depending on the size of your garden rows.
Plastic mulch's environmental effects have led some gardeners to avoid it in favour of biodegradable alternatives. According to Washington State University, several types of degradable mulch films have been developed. Gardeners may also choose to mulch with opaque brown Kraft paper, organic mulches such as straw, hay and grass clippings, or newspaper. Many of these mulches provide similar heat-increasing and weed control properties to those of black plastic.
- Oregon State University; Black Plastic Can Help Your Garden Grow; Peg Herring
- Michigan State University; Using Black Plastic Mulch; J. Lee Taylor
- Washington State University: Alternative to Plastic Mulch
- Fort Valley State University: Black Plastic Mulch
- Virginia Tech; Mulches for the Home Vegetable Garden; Diane Relf
- Oklahoma State University; Use of Plastic Mulch and Row Covers in Vegetable Production; Dean McCraw, et al.