Backyard Gardener: Extending the growing season with low tunnels
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Hello Mid-Ohio Valley farmers and gardeners! This week I want to talk about extending the growing season for our cool season vegetables. Many cool season veggies such as kale, Swiss Chard, spinach, many lettuces, broccoli, and Brussels sprouts will thrive deep into the winter. Many gardeners harvest spinach and kale the week after Christmas.
In West Virginia, the first fall frost usually marks the end of the growing season. However, there are many ways to garden almost year-round. One economical method used to extend the season is low tunnel technology.
Low tunnels allow producers to achieve a four-season garden by creating a protected environment over crops. In the fall while mild temperatures still prevail, low tunnels can be used to raise the average daily temperature, and they also protect crops from low temperature injury and offer wind protection during the winter.
The mini-greenhouses provide the means for producers to grow cool-season vegetables and hardy root crops well into the winter months.
A scaled down version of a high tunnel, low tunnels are constructed of wire or pipe hoops that support clear plastic or fabric row covers. Construction is relatively easy. Small low tunnels can be built using nine-gauge wire hoops approximately 18 inches in height. These types of low tunnels are best suited to short-term frost protection.
A more effective low tunnel design uses a larger hoop constructed from metal or plastic pipe. The hoop is 4 to 6 feet wide and approximately 40 inches tall at the center. A 10- to 14-foot wide row cover is placed over the hoops. Remember to use an ultraviolet-stabilized agricultural grade fabric or plastic for the row cover.
Clear polyethylene plastic is not recommended in the fall, because it can overheat and increase the relative humidity. Weigh down one side of the fabric using landscaping staples or soil and bricks. Then, secure the other side with rocks or sandbags. This makes it easy to lift the cover off.
Row covers can be used over hoop structures for low tunnels. Agriculture floating row covers come in different grades to protect against frost, heavy freezes and pests. You will need to decide what your plan is with your low tunnel and purchase appropriate grade row covers. One major advantage of using hoops with row covers is it keeps the weight of the snowfall off your crops.
A 10- to 14-foot-wide row cover blanket is placed over the hoops and secured taut and tightly to avoid winds removing cover and snowfall crushing. Typically, the ends are tied
down with stakes and string. There are row cover snaps or clips that can be constructed from PVC tubing or purchased to hold the row cover to the individual bows.
At each hoop, the sides of the row cover can be secured with bricks, heavy rocks or sandbags. Consider using objects heavy enough to hold down sides but are not permanent (at least on one side), as you will need to get into the low tunnel to check and work crops. If just overwintering crops and not harvesting, you can secure the cover more permanently by burying the sides or weighing it down with heavier objects.
Most row covers, depending on grade, will provide protection down to 24 to 28 degrees F and are water, air and light permeable. During colder temperatures, a second layer of row cover or a heavier weight row cover can be used to provide greater protection.
During the winter, a layer of 4 or 6 mil agriculture grade plastic is placed over row cover and secured to allow snow to slide off the structure. On warmer, sunny days, the plastic will need to be lifted to allow ventilation of the tunnel to avoid plants becoming overheated.
Low tunnel clips can be used to secure the lifted sides to the hoops. The plastic can cause moisture build-up inside the tunnel, therefore use only as needed.
Row covers can be removed when sunny and ambient temperatures are above 55 degrees F for cool-season crops, but may need to be placed back on in the evenings and overnight when temperatures drop into the 30s.
Most cool-season crops need a soil temperature greater than 40 degrees F for seeds to germinate and transplants to thrive. Constructing and using a low tunnel in the fall and throughout the winter into the spring creates the soil temperatures needed for production.
If constructing the low tunnel during the winter, cover the tunnel and let it sit empty for a few weeks to allow the soil to reach the desired temperature.
Heavy snowfall can collapse a low tunnel. To prevent this, cover with a plastic sheeting, construction-grade plastic is acceptable, for snow to slide off of the hoop structure. Reinforcing with a top railing also provides strength against snow and wind.
Livestock-panel-style low tunnels can be left year-round and used as a trellis system for vine crops, such as beans, cucumbers, melons and peas during the warmer months without the row cover.
Although unheated, low tunnels can be used to grow cool-season vegetables throughout the winter. The soil inside the tunnel is much warmer than the snow-covered ground outside. Spinach and kale are cold-hardy vegetables and can be harvested throughout the winter in a low tunnel. Other cool-season vegetables will need to be harvested before the coldest temperatures of winter or left to overwinter in the tunnel to get an early start in the spring.
Looking for more information on extending the gardening season? Check out our WVU Extension Gardening page at extension.wvu.edu/lawn-gardening-pests/gardening. Contact me at the Wood County WVU Extension office at (304)-424-1960 or at jj.barrett@mail.wvu.edu with your questions. Until next time, Good Luck and Happy Gardening!