LSU AgCenter Horticulturist Offers Ways To Extend Garden Season

Thomas J. Koske  |  12/22/2005 11:31:42 PM

News You Can Use For January 2006

To get the most out of a garden, you can extend the growing season by sheltering plants from cold weather in winter and early spring, says LSU AgCenter horticulturist Dr. Tom Koske.

"Very ambitious gardeners harvest greens and other cool-weather crops all winter by providing the right conditions," Koske says, adding, "There are many ways to lengthen the growing season, and your choice depends on the amount of time and money you want to invest."

Cold frames and hot beds are relatively inexpensive, simple structures for providing a more favorable environment for growing cool-weather crops in the very early spring and even through the winter, the horticulturist says.

"Some structures are elaborate and require a large investment but are reasonable for those who are serous about having fresh vegetables during the winter in the northern half of our state," he says.

Cold frames like "hoop houses" have no outside energy requirements, relying on the sun as their sole source of heat. Hot beds are heated by soil heating cables or fresh, straw-like manure buried beneath the rooting zones of the plants.

"The ideal location for a cold frame is a southern or southeastern exposure with a slight slope to ensure good drainage and maximum solar absorption," Koske says, adding, "A wind-sheltered spot with a wall or hedge to the north will provide protection against winter winds."

Some gardeners make their cold frames lightweight enough to be moved from one section of the garden to another. Designs in cold frames include passive solar energy storage or a light bulb for minimal heat.

In early spring, a cold frame is useful for hardening off seedlings started indoors, Koske says.

"This hardening-off period is important, since seedlings can suffer serious setbacks if they are moved directly from the warmth and protection of the house to the garden," he says. It also is possible to start cool-weather crops in the cold frame and either transplant them to the garden or grow them to maturity in an open (uncovered) frame.

Spring uses of the cold frame center on plant propagation. Young seedlings of hardy and half-hardy annuals can be started in a frame many weeks before they can be started in the open, according to Koske. Or, the soil in a portion of the bed can be replaced with sand or peat moss or another light medium suitable for rooting cuttings and for starting sweet potato slips.

Frames can be built from a variety of materials, with wood and cinder block being the most common, the horticulturist says. If you use wood, Koske advises choosing wood that will resist decay, such as a pressure-treated wood.

The dimensions of the frame will depend on amount of available space, desired crops, size of available window sash and permanency of the structure. "Do not make the structure so wide that weeding and harvesting are difficult," Koske says, explaining that 4 to 5 feet is about the right width to reach across.

"Insulation may be necessary when there’s a cold snap," Koske says. "A simple solution is to throw burlap sacks over the sash at night to protect against freezing."

Dry leaves or pine straw also may be used. And bales of straw or hay may be stacked against the frame, especially on the north side.

Ventilation is most critical in the late winter, early spring and on all clear, sunny days when temperatures rise, according to Koske, who says the sash should be raised partially to prevent the buildup of extreme temperatures (90 F) inside the frame. Lower or replace the sash each day early enough to conserve some heat for the evening.

The horticulturist also says you may convert your cold frame to a hot bed.

For a manure-heated bed, dig out the floor, add a 12-inch layer of straw-like manure and cover with 6 inches of good soil. The composting manure will give off heat.

For an electrically heated bed, dig out the floor and lay down thermostatically controlled electric cable in 8-inch long loops. Cover with 2 inches of sand or soil and lay out hardware cloth to protect the cable. Then cover with 6 inches of good soil.

More gardening information is available at your local LSU AgCenter office. In addition, look for lawn & gardening and Get It Growing links in the LSU AgCenter Web site:


On the Internet: LSU AgCenter:
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Source: Tom Koske (225) 578-2222, or

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