by Brad Cochran, CARD Extension Agent, firstname.lastname@example.org
Have you ever dreamed of a big, juicy tomato in May or June? Or maybe a fresh salad with lettuce, spinach, carrots and radish during Thanksgiving or Christmas? Perhaps you sell produce at a local farmers market and would like to have products to sell earlier and later into the market season? If you answered yes to any of these questions, then taking advantage of growing season extension practices may be right for you. Generally speaking, season extension can be defined as anything that allows a crop to be grown beyond its normal outdoor growing season. Some common examples of season extension are greenhouses and high tunnels, but are there other options? You bet!
The biggest problems and obstacles with greenhouses and high tunnels are the cost of construction (though the Natural Resources Conservation Service does have a cost-share program to assist in purchasing high tunnels) and the hefty footprint they leave on your property. For small-scale growers in particular, the cost of these structures may be too much to even consider season extension as an option. However, there are a couple different options that are available to you at a much lower cost and with a very small footprint. These options are low tunnels and cold frames that allow for season extension.
Low tunnels are essentially a miniature version of high tunnels that can be attached directly to raised beds or placed in the ground for traditional growing. The low tunnels are covered with greenhouse-grade plastic that heats up the sunlight and keeps the soil and plants warmer than they would be if left exposed to the elements. The frame of the low tunnel can be constructed from a number of materials, but the most common are metal conduit, bent and shaped to fit the site where it will be placed, or PVC pipe bent to fit the location of use. The metal conduit will be much sturdier against the elements but more expensive than PVC.
Cold frames are structures that have a hinged lid on top to allow you, as the grower, to keep it sealed shut or be open for increased airflow. They can be made from a variety of materials ranging from PVC, wood or metal frames and covered with greenhouse grade plastic or twin-wall polycarbonate greenhouse material, or they can be constructed using recycled home windows or other recycled materials. Cold frame kits can also be purchased from many online retailers and typically range in price from $80–$250. Homemade cold frames can also be built for less than $20 using recycled materials. They can be standalone structures placed directly on the ground or mounted to raised beds. Designs and growing information for cold frames can be found in The Cold Frame Handbook by Derek Weiss.
So why is season extension so important? Because it allows for additional weeks of growing fresh, local produce available for family consumption or for sale in local markets or restaurants. Low tunnels and cold frames are great at extending your cool season harvest of lettuces and greens (collards, mustard, turnip, etc.), radishes, carrots and other vegetables well into the holiday season. Low tunnels and cold frames are also great ways to get a head start on the growing season in the spring. They enable you to directly plant cool season crops earlier in the year and also create a place to “harden off” plants started from seeds, like tomatoes, peppers and others. Cold frames in particular are great devices to have in place for the hardening-off process, in which you bring seeds started indoors under grow lights outdoors to get the plants adjusted to cooler temperatures. Cold frames are places where plants are almost weaned away from high temperatures indoors, but can still be protected from the elements that can come with a late frost up until mid-May.
Keep those plants protected in low tunnels or cold frames, get your seedlings hardened off earlier, and extend your growing season and your overall production starting now. Low tunnels and cold frames are easy to construct and relatively inexpensive for all of the wonderful things they can do for your garden production. Happy growing!