Extending the Garden Season

Does it seem like the garden season has flown by this year? There are several structures that extend the season, both by allowing plants to be grown earlier in the spring and later in the fall. Although primarily used for vegetables, flowers and other ornamental have been known to make an appearance as well.

Cold frames are the most common, useful, and versatile of the structures used as season extenders. They are a simple, easily made structure that essentially functions like a miniature green house. They can be made from readily available materials, including cast-off glass or plexiglass windows, plastic covers with wooden frames, lumber remnants, or even straw bales. Not only are they ideal for early spring planting transplants, but are very useful for growing salad crops after the regular season is long over, forcing bulbs in the winter, or storing root vegetables like carrots and parsnips.

Ideally, a permanent cold frame should be made from wood with a hinged lid. It will be necessary to prop the lid open on very sunny days when the temperature inside the frame gets hot enough to wilt the plants. Angling the top will give the added benefit of capturing the maximum amount of winter sun. Cold frames can be filled with soil and planted directly or can be filled with pots and used for germination, hardening off plants, or forcing bulbs.

A hot bed is a second type of structure that can extend the gardening season. A cold frame becomes a hot bed with the addition of some type of heat added beneath it. Typically, a heating cable is placed 3–5 inches below ground level and covered with sand, pea gravel, or a growing medium. The best use for a hot bed is to start seedlings in the spring rather than under artificial light.

Low tunnels are another way to extend the season 6–8 weeks longer. A series of hoops, about 4 feet tall, made from rebar, electrical conduit, or PVC pipe are bent and inserted into the ground or a raised bed. The hoops are covered with 4–6-millimeter polyethylene that is firmly secured by burying the edges and weighting down the ends. Similar to the cold frames, these will heat up on sunny days and must be monitored, opening the ends when necessary to prevent overheating. Since the plastic is not permeable, soil moisture must also be monitored and crops may need some additional water during the winter.

Floating row covers are one last way to extend the season. This lightweight fabric is available in varying thickness, depending on the use. It is draped over the plants and often held up by hoops similar to the low tunnels, although not as tall. This fabric is permeable to light, water, and air, so it is not necessary to open it for heat or moisture regulation. They keep the plants 5-10 degrees warmer and provide frost protection, making them a valuable tool in both the spring and fall. In addition, they work well as insect protection for those plants that do not require pollination (broccoli and cabbage).

If gardening is your passion and you just need to do more than the short Wisconsin season allows, consider incorporating a cold frame, hot bed, low tunnel, or some floating row covers into your tool box.

Carol Shirk

Certified Master Gardener