One of the challenges of living in Wyoming is the late frost in the spring and the early frost in the fall. This fact really shortens our growing season for vegetables unless we can provide some protection. Several techniques will lengthen the growing season, making it possible to begin earlier in the spring and end later in the fall. These techniques are cold frames, hot beds, hoop houses, cloches, and floating row covers.
One common method is a cold frame; a simple structure that provides warmth from the sun and blocks the wind. The sun’s rays enter through a transparent cover which creates a greenhouse effect that heats the interior of the cold frame.
The most common use of cold frames is to expand the growing season by several months. Many gardeners use cold frames to harden off transplants, but another good use is raising cool-season vegetables. Alternatively, in the fall these same crops may be grown in the cold frame through November. A disadvantage can be the small size, unless you only have a small space.
On a sunny day, air in cold frames can get too hot for plants; often the lid needs to be propped open so cool air may enter the frame. Some mail order garden catalogs offer temperature controlled cold frame hinges that automatically open and close to vent the frame.
In general, cold frames should be located against a south or west wall near the building foundation to take advantage of its heat. Portable cold frames built of lightweight material allow the gardener to move the frame to different sun exposures as seasons and plants change. Heating cables can be added to the soil to encourage root growth early and late in the year, along with adding some heat to the cold frame.
Frequently used for tomatoes or peppers, cloches and hot caps add three to four weeks to the spring growing season. There are many variations on cloches, but generally they are any transparent “house” that covers a single plant. The most common cloches are empty gallon milk jugs with the bottom cut out. A popular commercial product is the “Walls of Water” plant surround. Another inexpensive cloche is made by covering a tomato cage with clear polyethylene. Like cold frames and hoop houses, cloches should have some type of opening to allow hot air to escape on sunny days.
Floating row covers are made of spun polyester or polypropylene and look like fabric. They are permeable to light, water, and air. Floating row covers have multiple uses in the garden. Row covers keeps plants 5-10 degrees warmer than the surrounding air and provides frost protection to a low of 28 degrees. They protect tender plants from wind and hail damage. In addition, row covers are an excellent barrier to insects. This material is my favorite since it offers so many possibilities and accommodates many different situations.
A hoop house is similar to a cold frame, only larger. Metal or plastic pipes are bent into a series of hoops that are stuck into the ground or attached to a raised bed. The hoops are covered with polyethylene, (milky plastic) and it is not heated and does not use growing lights.
Gardeners can expect an additional month or two of growing time inside a hoop house in the spring and fall. Like cold frames, hoop houses must be ventilated on warm days. The advantage of a hoop house is you can walk inside and the larger area provides more heat in the early spring or late fall. Another advantage is in watering, picking, and other management chores, since you do not have to take the covering off to perform these tasks.
In Wyoming, we can gain additional growing time from April until December in a hoop house; which in most cases is over double the growing season.
The real advantage of any of these systems is the added growing season and the opportunity to replant cool season vegetables in the spring and plant them again at least once more in the fall. This allows harvesting three to four times the amount of vegetables from the same area of land. With any system there will be a little more management involved, however the benefits can outweigh the time and the cost of these systems is minimal.
Trade or brand names used in this publication are used only for the purpose of educational information. The information given herein is supplied with the understanding that no discrimination is intended, and no endorsement information of products by the University of Wyoming Extension is implied. Nor does it imply approval of products to the exclusion of others, which may also be suitable. The University of Wyoming is an equal opportunity/affirmative action institution.
Scott Hininger is with the Sheridan County Extention office.