Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, August 12, 1993 TAG: 9308110100
SECTION: CURRENT PAGE: NRV-8 EDITION: NEW RIVER VALLEY
SOURCE: Joe Hunnings
DATELINE: LENGTH: Medium
There are many ways to lengthen the growing season, and your choice depends o n the amount of time and money you want to invest.
Cold frames, hot beds
Cold frames, sun boxes and hot beds are relatively inexpensive, simple structures for providing a favorable environment for growing cool-weather crops in the early spring, the fall and even into the winter months. Some are elaborate and require a sizeable investment, but are reasonable for those who are serious about having fresh vegetables during the winter.
Cold frames and sun boxes rely on the sun for their source of heat, so they need no outside energy source. On the other hand, hot beds are heated by soil-heating cables, steam-carrying pipes or by fresh, straw-rich manure buried beneath the root zones of the plants. Heat is collected by all these structures when the sun's rays pass through the clear plastic, glass or fiberglass sash or cover.
The ideal location for a cold frame is a south-facing or southeastern exposure with a slight slope to ensure good drainage and maximum solar absorption. A sheltered spot with a wall or hedge to the north will provide protection against winter winds. Sinking the frame into the ground somewhat also will provide protection and uses the earth for insulation.
To simplify access, provide a walkway to the front, adequate space behind the frame to remove the covering and weights to ease raising and lowering of glass sashes.
Some gardeners make cold frames lightweight, so they can be moved from one section of the garden to another. New designs in cold frames include passive solar energy storage. For example, barrels painted black and filled with water absorb heat during the day and release it at night. The solar pod is one design which provides this type of heat storage.
Other cold frames are built with a high back and a steep glass slope facing south to increase solar gain and are insulated well. These may also include moveable insulation that is folded up during the day and down at night or during extremely cold weather to provide added protection.
Fall is a good time for sowing cool-weather crops in frames. If provided with adequate moisture and fertilization, most cool-season crops will continue to grow through early winter in the protected environment of the cold frame. Depending on the harshness of the winter - and whether additional heating is used - your frame can provide fresh greens, herbs and root crops throughout the cold winter months.
Growing frames can be built from a variety of materials, but wood and cinder blocks are the most common. If you use wood, choose a decay-resistant type, such as exterior plywood pressure-treated wood. Never use wood that has been treated with creosote or with pentachlorophenol - or "penta" - since these substances can harm growing plants.
Wood frames are not difficult to build. Kits can be purchased and easily assembled; some kits even contain automatic ventilation equipment.
There is no standard size cold frame. The dimensions of your frame will depend on your situation. Amount of available space, desired crops, size of available window sash or other suitable covering and permanency of the structure all should be considered. Do not make the structure too wide for weeding and harvesting; three to four feet is about as wide as is convenient to reach across. The sash of the frame should be sloped to the south to allow maximum exposure to the sun's rays.
Insulation may be necessary when a sudden cold snap is expected. A simple method is to place burlap sacks filled with leaves over the sash of the frame at night to protect against freezing. Or, bales of straw or hay may be stacked against the frame.
Ventilation is most critical in the late winter, early spring, and early fall on clear, sunny days when temperatures rise above 45 degrees. The sash or covering should be raised partially to prevent buildup of extreme temperatures inside the frame. Lower or replace the sash each day early enough to conserve some heat for the evening.
Joe Hunnings is the Virginia Cooperative Extension Service agent for agriculture in Christiansburg. If you have questions call the Montgomery County extension office at 382-5790.
by CNB