   Year-Round Vegetable Gardening - November 9, 2005 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County The Verde Valley is an excellent location for vegetable gardening. Warm season crops have a long growing season and most cool season crops can also be grown successfully. Really devoted vegetable gardeners use strategies to extend the growing season for warm season crops. These strategies are often referred to as season extenders. Some examples are using transplants, hot caps, walls of water, cold frames, floating row covers, and hoop houses. Season extenders are used to get an early statrt in spring and to moderate winter temperatures to increase productivity of cool season crops. December, January, and February typically have the lowest temperatures and have dropped as low as 8, 13, and 9 degrees F respectively. Fall freeze probabilities say that there is a 50% chance of reaching 32.5 degrees F by November 9 and the latest freeze date on record is November 28. Spring freeze probabilities say that there is a 50% chance that the last spring freeze (32.5 degrees F) will occur by April 1 with the latest freeze date on record being April 27. All weather data presented above is from Tuzigoot National Monument in Clarkdale. Sedona has very similar fall temperatures to Tuzigoot, but the late spring freezes are two to three weeks later. Jerome is in the “banana belt” and actually stays warmer than Clarkdale or Sedona in the fall and spring freeze dates are in between Clarkdale and Sedona. The best fall season extenders are cold frames, floating row covers, and hoop houses. Cold frames can be built from available materials or purchased readymade from gardening suppliers. I built one a few years ago from a couple of salvaged double glazed windows (see the February 2, 2000 Backyard Gardener column) and it lasted 5 years until the glass got broken. Straw bales with windows on top of them work well too. Readymade cold frames are moderately expensive (about $120). The model I am most familiar with is glazed with insulated polycarbonate panes and can be equipped with an automatic vent opener. Cold frames are excellent for growing small amounts of fresh lettuce and greens during the winter. Floating row covers are simple, effective way to provide a growing slight advantage to cool season crops during the fall. Row cover material is spun bonded polyester formed into sheets that allow sunlight, air, and some water to penetrate, but hold in heat, protect crops from wind, conserve moisture, and exclude some insect pests and birds. Row cover material is white and available in different thicknesses that vary in their frost protection ability and light transmittance efficiency. Row cover is relatively inexpensive and usually lasts for two growing seasons. Hoop houses (also called high tunnels) are larger than a cold frame and smaller and less technically advanced than a greenhouse. Again, there are homemade and readymade versions. Homemade hoop houses are usually constructed out of PVC pipe and covered with inexpensive clear visqueen-type plastic sheeting. They are also temporary structures. The PVC is anchored to the ground and bent to create an arched roof like a Quonset hut. Look at the design by Travis Saling available on the Internet at www.westsidegardener.com/howto/hoophouse.html. The instructions are clear and the materials list included. It looks like you could construct a 10 x 20 foot hoop house for about $50. Keep in mind that a hoop house is not airtight or designed to be heated. If you find yourself wanting to go this route, start looking at greenhouses. Hot caps and walls of water are most frequently used to get an early start on the summer growing season. Hot caps can be constructed out of one gallon plastic milk jugs that have the bottoms cut out or cones of wax paper. Walls of water are commercially produced devices that use water as thermal mass and protect small plants from frost. I have never used them, but know many people that have used them successfully. Any seedlings started indoors or transplants purchased from garden centers should be acclimated to the cold outdoor temperatures. Leafy vegetables and root crops can be planted in the fall. This includes lettuce, kale, chard, arugula, spinach, beets, turnips, radishes, onions, and garlic. You can also grow brussel sprouts, broccoli, cauliflower, and peas during the cool season. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |