 |
|
|
|
| |
The Garden Plot for July 03, 2009
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: “High Tunnels”
Ways to extend the growing season are always foremost on the minds of Montana gardeners. One way is to build temporary or semi-permanent plastic covered structures. We used to call them cold frames. The new term is “high tunnel” and the new name implies the difference. Cold frames were usually short, 2-5’ tall structures. High tunnels are unheated, plastic-covered frames that look like greenhouses. They are usually covered with two layers of plastic. High tunnels can be just tall enough to stand up in, or as tall as the tallest greenhouses. High tunnels differ from greenhouses in three ways. They do not have a heat source, they usually do not have a fan that inflates an area between the two layers of plastic, and they can be moved more easily than greenhouses, which have a permanent foundation. Therefore, high tunnels are cheaper to construct than greenhouses.
To build a high tunnel, you need metal or PVC hoops and greenhouse-grade plastic that has been treated so that it does not break down in the sun rapidly. If the plastic is not a greenhouse-grade plastic, it can break down after only one sunny, Montana summer. Greenhouse supply companies have various materials for attaching the plastic to the hoops. First, you install a wood frame around the base and ends of the high tunnel. My favorite plastic attachment method is a 2” wide metal, grooved base screwed into a wood frame, and wiggly wire (called wirelock) that holds the plastic into the metal base. One low-tech method I saw that worked well on short high tunnels, in low wind areas, was rope criss-crossed back and forth over the plastic and hoops from one end of the high tunnel to the other. The rope was held down with metal posts placed every 8’ on either side of the high tunnel.
Building the high tunnel is just your first step. The second step is to do a soil test and amend your soil as needed. Design your beds inside the tunnel for maximum air movement. Disease can become a problem in high humidity plastic tunnels without adequate aeration. Raised beds work best.
Next, pay attention to night-time temperatures. If temperatures below 30 F are predicted, make sure you have frost protection on hand for frost susceptible plants. Row cover can be used to protect warm season crops. Row cover comes in several thicknesses; the heavier the fabric, the more frost protection. Row cover for frost protection works best if it does not touch the plants, but instead allows air movement through and around plants. You can use wire or PVC hoops to keep row cover off of plants. In some high tunnels, people have built permanent, removable frames to support the row cover.
You can further encourage ripening of warm season crops by heating up the high tunnel soil with plastic mulches or weed mat. Black plastic is the most common, but researchers have experimented with colored (especially red and green) plastic mulches designed to increase the yields of specific warm season crops.
The Missoula County Extension Service will be sponsoring a farm tour of vegetable production season-extending techniques, including greenhouses, high tunnels, cold frames, and in-field season-extension products on Saturday, June 27 at 3 pm at Biodesign Farm in Stevensville. For more information call 258-4205.
For more information about high tunnels, contact your local county extension agent.
Helen Atthowe's new short program of gardening tips
|
|
|
