Mulches and Row Covers

Mulch is any material (natural or artificial) used to cover the soil’s surface and modify the soil environment. Natural mulches include bark, wood chips, straw, manure, compost, or sawdust. Artificial or synthetic mulches include plastics, paper, or foils. Row covers are materials that cover plants and create an altered environment around them. 

The advantage associated with mulches and row covers is to creating conditions that improve the crop’s growth. Some common benefits of mulches and row covers are significant temperature modification, more efficient water use, reduced fertilizer losses, improved weed and insect management, and reduced fruit losses due to rots.

Mulches

The most popular mulches used in agriculture are clear and black polyethylene (plastic) films. Use clear plastic when needing higher soil temperatures early in the season for crops like cucumbers, melons, and sweet corn. Soil temperatures are generally 10 °F warmer under clear than black plastic and 15 °F to 20 °F warmer than bare soil. This extra warmth usually results in high yields for early spring-planted crops. One disadvantage associated with clear plastic is the need for good weed control under the mulch. Often, soil fumigation is used in conjunction with clear plastic to manage weeds, diseases, and insects better.

There are many different mulch colors and compositions available for use. Black is the most common color, but there are instances where green “IRT” mulches are used where soil temperatures need to be warmer. Silver or aluminized mulches have been shown to repel certain insect pests (aphids, thrips). In cloudy areas, red mulches reflect more light back into the plants, which increases productivity. In the heat of summer, white mulches reflect heat, and soils stay cooler. Lay the mulch 3 to 6 days before planting to obtain soil temperature benefits. If you fumigate under clear mulch, allow 21 days for fumigants to dissipate before planting.

In a typical mulching operation, a 3- or 4-foot-wide mulch plus drip irrigation tape are laid simultaneously. Mulches will work with furrow irrigation so long as furrows and plants are very close to the plastic edge, allowing young plants access to the water. 

Other options are photodegradable and biodegradable plastic mulches. These usually cost more than regular plastic films but reduced disposal costs may offset the difference. Over time, sunlight causes photodegradable mulches to become brittle and break down. One disadvantage of the degradable mulches is that small pieces of film tear off and are blown around by the wind. In addition, they are weakened by soil microorganisms in high soil moisture and temperatures. One advantage is that they can be incorporated into the soil at the end of the growing season.

Plastic mulches are commonly only used once, removed from the field, and disposed of at the end of the growing season. On small farms, it is often removed by hand while on larger operations, tractormounted mulch removal equipment is available. Highquality plastic mulches can be used for two successive crops during the same season if you are careful. Crop foliage and weeds may increase the difficulty of mulch removal. When replanting through or removing the plastic mulch, eliminate as much vegetation as possible. Use glyphosate or paraquat to desiccate both weeds and residual crops or delay plant removal until after a hard frost kills the crop.

After the mulch has been removed from the field, dispose of used plastic in an environmentally appropriate manner. Regulations on disposal vary, so contact your local solid waste authority for recommended disposal methods. Some plastics can be recycled, and specific programs for recycling agricultural plastics may be available. Consult with your state authorities to learn the specifics of plastics disposal.

Organic mulches (straw, sawdust, bark, etc.) reduce soil temperatures, improve soil moisture control, and help reduce soil erosion (wind or water). Achieve good weed control by applying organic mulch thickly (>2 inches). Organic mulches are often bulky, hard to apply, and may be difficult to source. There have been instances where insect (slugs, cutworms, etc.) and rodent damage occurs when using organic mulches. Organic windbreaks are commonly used to provide plant protection during establishment and can be used with plastic mulches.

Row Covers

Row covers are fabric or plastic materials which cover plants and hasten crop maturity, provide frost or hail protection, and also may exclude certain insect pests from gaining access to the crop. Floating row covers are made of lightweight spun fibers (polyester or polypropylene) that lay loosely on the plants or can be suspended over the plants with wire supports.

Floating row covers are used to cover low growing vine crops or to protect upright plants like tomatoes and peppers. Plants may be injured by abrasion when the floating row cover rubs on the plant in windy conditions. Frost damage can occur with floating row covers, particularly where the covers touch the leaves. Air temperature under the floating row cover is 3-5°F warmer at night, and more than 10°F higher during the day than the outside air temperature.

Clear and translucent plastic row covers (low tunnels) are another option to enhance early season plant growth. Plastic row covers are supported by wire hoops placed at 3 to 6 foot intervals in the row. Air temperatures under the low tunnels on warm sunny days can be 25-30°F warmer than outside, so plants may experience heat injury. Provided the temperatures under the low tunnels do not exceed 90°F, most warm season crops are not damaged. At higher temperatures, crops can be stressed, which inhibits growth, causes flower abortion or bolting.

Fabric and plastic row covers are often used in combination with plastic mulches. Most research shows that plants grown on plastic mulches under row covers mature earlier and yield more than those grown outside on bare ground. Several different companies make equipment that lay plastic mulch and row covers in one operation. Plastic mulches, fabric, and plastic row covers can be costly, and prices change rapidly because they are manufactured from petroleum. Consult your dealer for current prices.

More Information

• Using Mulches in Utah Landscapes and Gardens
• Use of Plastic Mulch for Vegetable Production
• Row Covers
• Low Tunnels: A Low-Cost Protected Cultivation Option