Extending Season for Vegetable Production

Season Extending Materials

Over the past 20 years, UNH researchers have developed and demonstrated integrated growing systems that extend the growing season, while increasing yield and enhancing produce quality.

Synthetic plastic mulches have proven to be an invaluable production tool in the Northeast. Black polyethylene, the primary type of mulch used by commercial growers, warms the soil, controls weeks and prevents both soil water loss and nutrient leaching. Clear plastic mulch warms the soil more than black, allows light to penetrate and weed growth underneath. Dr. Brent Loy of UNH’s plant biology department developed solar mulch, which allows n ear-infrared light to pass through the mulch but blocks photosynthetically active light, reducing weed growth. UNH researchers have also studied the effects of colored mulches. Different colors reflect certain wavelengths of light back towards the plants, affecting plant growth, crop yield, and insect feeding activity. Research at UNH showed tomatoes grown on raised beds with black mulch produce greater yields when white plastic mulch is laid between the rows than when the ground between the rows remains bare.

Row covers are plastic or non-woven materials placed over field-grown crops to promote earlier yield or exclude insect pests. These row covers are supported by wire hoops or "floated" as large sheets directly over crops.

Slitted rowcovers supported with wire hoops benefit warm season crops such as cucurbits (melons, cukes, squash and pumpkins), tomatoes, peppers, eggplant and also with summer squash in very windy areas. Non-woven covers are lightweight and made of spunbonded polyester or polypropylene. Crops such as cucurbits (melons, cucumbers, squash and pumpkins), root crops, leafy greens, beans, and sweet corn may be covered without the use of hoops.

Spunbonded covers are useful for insect control because they physically exclude insects from the growing environment. For example, growers who apply row covers to root crops and members of the cabbage family at the time of planting can minimize damage from root maggots and flea beetles. Other insects controlled by these covers include the first generation of corn borer, carrot rust fly, Mexican bean beetle, striped cucumber beetle and various species of aphids.

High tunnels are simple, greenhouse-like structures used for extending the season in the spring and fall by raising the temperature in the growing environment. The basic structure consists of metal bows anchored to posts driven in the ground and covered with one layer of greenhouse-grade polyethylene plastic. The tunnel ends are also framed and covered to accommodate doors, often large enough for small mechanical equipment. High tunnels typically contain no heating appliances and no exhaust fans for ventilation (although we recommend an emergency heating system for extremely cold nights). Growers rely instead on solar radiation for heat, and three- to four-foot, roll-up sidewalls to provide ventilation in high tunnels. Trickle (drip) tubes laid on the soil surface and covered with a 6-mil sheet of black plastic supply water. The black plastic functions to warm the soil, decrease water loss, and provide weed control. Vegetable crops recommended for high tunnel production include tomatoes, peppers, cucumbers, melons and summer squash. Growers do not use black plastic mulch for direct-seeded crops.