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New Mexico State University

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Row Covers, Plastic Mulches Protect Spring Vegetables

LAS CRUCES - Vegetable growers can use fabric row covers and sheets of plastic mulch to give tender crops an early start and increase yields, said a New Mexico State University horticulture specialist.


"Harsh spring weather is a major concern for most small vegetable growers in northern New Mexico, as well as gardeners," said George Dickerson with NMSU's Cooperative Extension Service. Wind injures tender vegetables and increases water evaporation from the soil, creating a hard crust. Late spring frosts and hail can kill plants, leading to expensive replanting and delays in crop maturity.

"If you're trying to get your crop to market early to capitalize on higher prices, you need to get your crop in the ground early and encourage optimum growing conditions with growth-enhancing techniques," Dickerson said.

Plastic mulches warm the soil and encourage early root production. Clear plastic heats the soil but encourages weed growth. Black plastic provides better weed control and moderate soil heating.

An older technique for protecting vegetables is placing clear plastic tunnels over the plants.

"The tunnels act like mini-greenhouses in warming the air around the vegetables, but if they're not ventilated during the day, they can cook the plants," Dickerson said.

Although more expensive than plastic tunnels, fabric row covers provide weather protection and better ventilation, Dickerson said. Row covers can be floated over the crop or supported with wire hoops.

"We have been able to protect tomato transplants down to 28 degrees Fahrenheit at many locations throughout the state," Dickerson said. "Row covers work best in combination with a black plastic mulch."

Last year, Extension faculty did row cover experiments with butternut winter squash at NMSU's Agricultural Science Center at Los Lunas. Because of frost, uncovered plots had to be replanted twice. Yields from row-cover plots were triple those of unprotected plants.

"Row-cover plots at Los Lunas were 19 days earlier than uncovered plots," he said. "This not only resulted in greater yields but also a doubling of the price the squash sold for at the growers' market."

Row covers are made from spider web-like material of polyester or polypropylene. When these fabrics are bonded by heat and pressure, they are flexible and porous, allowing ventilation and minimizing overheating. "These fabrics usually have a white sheen, but light reflection is minimal," Dickerson said. "Light penetration through the fabric averages about 80 percent and is not a significant factor because our light is so bright here in the Southwest."

Most of these fabrics also have an ultraviolet light inhibitor that delays their breakdown, making them reusable for several years.

Wire hoops are generally used with row covers over tomatoes and peppers. Row covers are secured with fabric pins or soil piled on the edges of the material.