Season Extension Techniques for Home Vegetable Gardens - U of I Extension

News Release

Season Extension Techniques for Home Vegetable Gardens

This article was originally published on April 14, 2010 and expired on July 31, 2010. It is provided here for archival purposes and may contain dated information.

Vegetables grown in home gardens are very sensitive to cold weather, noted a University of Illinois Extension horticulture educator.

"They are grown mainly during the frost-free periods so this poses a great challenge to home gardeners as the growing season is very short," said Maurice Ogutu. "For home gardeners to start growing vegetables early or continue growing vegetables into fall, it is essential to use techniques that will extend the growing season.

"The growing season can be extended by using the following techniques: plastic mulches that warm up the ground; row covers to protect the plants from freezing; or structures put around plants to keep plants warm when it is cold such as 'Wall O Water', hot caps, cold frames or hoophouses."

Plastic mulches warm up the soil in early spring giving the vegetable gardeners the opportunity to plant in early spring or in the fall when it is cooler.

"This gives a head start to warm-loving plants such as tomatoes, peppers, cucumbers, and melons," he noted. "Plastic mulches conserve moisture, and control weeds during the growing season. Plastic mulches also keep edible portions of vegetables off the ground."

To prepare, level the ground uniformly, irrigate or water so that the ground is moist before laying the plastic mulch. Install plastic mulch by stretching it tightly over the soil surface and burying all edges. Punch holes on plastic mulch based on within-row spacing of vegetables to be planted. Plant vegetable seeds or seedlings in the punched holes and cover with soil.

Check soil moisture content more frequently and water through planting holes. There are different types of plastic mulches, and some of the commonly used types are clear and black. Clear plastic mulch warms up the soil to higher temperatures than other types of plastic mulches.

"It can be used early in the season to warm up the soil then removed when plants are established and the ground has warmed up," he said. "Weeds tend to grow underneath clear plastic mulch but die due to high temperatures underneath the mulch.

"Black plastic mulch is the most commonly used plastic mulch in vegetable gardening. It warms up the soil in early spring or fall. It blocks sunlight so weeds cannot grow underneath the mulch."

There are other types of plastic mulches such as the dark green type that combines both good soil warming characteristics and blocking sunlight but it is more expensive compared to clear and black plastic mulches. There are also other types of plastic mulches that can warm up the ground in early spring such as red and blue types that can also be used by home vegetable gardeners.

"Row covers are put over growing plants to protect them from cold temperatures or insect pests," he said. "In order to extend the growing season, row covers can be used to protect plants from frost.

"Row covers enhance plant growth by raising day temperatures around the plants and insulating plants at night by trapping heat around the plants."

Install row covers by securing all edges so that they are not blown off by wind. The most commonly used row covers are made of either fabrics or plastic. Row covers made of spun bounded or woven fabrics allow air, water, and sunlight to pass through but they trap heat as well. They can also be used for insect pest control but need to be removed when plants are in full bloom to facilitate pollination.

The other type of row cover is made of slitted or perforated clear plastic which is heavier. It is supported with wire hoops when laid over the plants. The holes on clear plastic allow excess heat to escape, and the temperature underneath needs to be monitored carefully to avoid over heating on sunny days.

A cold frame is a bottom less structure put over plants with a glass or clear plastic on top or sides and it can be opened during the day time to allow ventilation.

"The glass or clear plastic is placed facing south or southwest so that it can let in and trap more heat from the sun," Ogutu explained. "They protect plants from frost but the temperatures need to be monitored in order to avoid over heating particularly on sunny days."

Hoophouse or hi-tunnel is a greenhouse frame covered with one layer of clear plastic. The ground is tilled and smoothened then metal frames are anchored into the ground and covered with clear plastic. The clear plastic cover on the sides can be rolled up to enable excess heat to escape during the daytime and rolled down at night to trap heat so that the environment around the plants is kept warmer.

"It is one of the most commonly used season extension technique by vegetable growers in Illinois," he noted.

Small protectors such as hot caps can be put around individual plants to act as a miniature greenhouse that traps heat from the sun and protect plants from frost. The caps are made of transparent waxed paper and can be used to protect one or two plants. The edges of hot caps can be secured with rocks. There are some hot caps made of clear plastic tubes joined together and filled with water and put around the plants. The water inside the tubes will trap heat from sunlight during the day time and releases the heat slowly at night to protect plants from freezing temperatures. They are sold under trade names such as "Wall O' Water".

"Home vegetable gardeners can also be innovative and creative in extending the growing season by using empty plastic milk jugs, or empty plastic soft drink bottles with the bottoms removed placed over plants to protect the plants from frost," he said. "Home gardeners can also use clear plastic fences or screens to protect the plants from freezing temperatures but tops need to be covered at night and if the temperatures are very low then other heavier insulating materials such as blankets, bed sheets, burlap, or canvas can be used. "

Source: Maurice Ogutu, Extension Educator, Local Food Systems and Small Farms,

Pull date: July 31, 2010