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University of Minnesota Extension

Starting Your Gardens Early

It may still be winter outside but it isn’t too early to start thinking about gardening. There are several different options a dedicated gardener can do to jump start their growing season. High tunnels, cold frames, hot beds, hot caps, and floating rows are a few options gardeners can use to extend their growing seasons.

Often there is confusion between a high tunnel and a greenhouse, the primary difference is that a high tunnel doesn’t include an elaborate heating or cooling system.  High tunnels provide a growing environment protected from many of the elements. High tunnels consist of a frame covered by a clear plastic of varying grades, and variations for entry and air flow.  In addition, high tunnels are a more controlled environment and in general have fewer insect or disease issues than traditional open growing gardens or fields. Overall high tunnels provide growers a simple, efficient way to protect crops from cold temperatures in spring or fall. Sizes of high tunnels vary; recommended minimum size is 10 to 12-feet wide, 20-feet long, with a 6 to 8-foot peak to provide efficiency with solar radiation.

For smaller, less expensive set up, cold frames are on option. A cold frame consists of a shallow, unheated box with a transparent cover. Cold frames strengths are to utilize the warmth of the sun to heat up the growing environment, and yet protect it from the cold. Cold frames should be constructed where they will receive southern exposure, and allow the grower to plant crops much earlier than in a traditional garden. Cool crops such as lettuce, kale, cabbage, cauliflower, or broccoli will perform well. Cold frames can also be utilized later in the season to ‘harden-off’ beds for heat-loving seedlings such as tomatoes, peppers, or eggplants.  Hot beds are another option, and have the exact same set-up as a cold frame, but are assembled with a bottom heat source.

There are a few options for simple, single plant or row season extension. Hot caps are a cone, bell, or tent shaped individual cover that acts like a mini greenhouse or high tunnel by trapping in heat from the sun. They can raise day and night time temperatures and allow for accelerated germination as well as provide protection from wind. Sometimes removal during the day is necessary because plants may become overheated.  

Sun traps cover multiple plants and are typically “U-shaped” structures that are open to the south. Floating rows are another multiple plant season extension option that are made of lightweight fabrics which allow for frost protection, allow sunlight to transmit through, but do not retain unnecessary heat.

For those of you looking at jump starting your gardens in the spring or stretching your growing seasons into late fall there are a lot of options you can try. From inexpensive hot caps, to cold frames, to more elaborate and much larger high tunnels, there are season extension tricks for all Minnesota gardeners to try.  For more information on high tunnels visit http://www.extension.umn.edu/garden/fruit-vegetable 

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