When the days start to shorten and night temperatures dip, do you often look over longingly at your neighbor's greenhouse, wishing you too could keep plants producing into the fall?
Investing in a greenhouse, especially a heated one, is an expensive step. For those of us who aren't quite ready to make the leap, there are a number of inexpensive options to protect plants from wintry weather. Cloches and cold frames can help extend the harvest of summer crops into fall, keep cool season crops growing through the winter, and help plants get a good start in the spring. They can protect plants from moderate frosts, and increase daytime temperatures by 5-20°F.
Cloches: Originally, cloches were constructed out of glass bell jars and were used to protect individual plants. However, glass is fragile and expensive. You can make similar cloches out of plastic pop bottles or milk jugs. Cut off the bottoms, take the lids off, and place them over individual plants. If your plants are too large or you have just too many, you can adapt this method. A cloche can also be constructed using 1/2" PVC pipe and sheets of plastic at least 5 feet wide and about 10 feet long. Cut 4 pieces of pipe into 5-foot lengths (angle the cuts) and bury each end into the soil at least 6 inches so that you have what looks like a series of crochet hoops. Space each pipe about 3 feet apart and then drape the plastic over them. You can secure the plastic by weighing down the ends with bricks or rebar or clip the plastic right to the pipe with large bulldog clips. Alternatively, you can use 10-gauge wire instead of the PVC pipe.
Cold frames: Cold frames are very much like mini greenhouses but with solid sides. They can be constructed using storm or sash windows and a simple wooden box or bricks for the base. No bottom is required which enables you to just lift the cold frame and move it around your garden. One trick to keep in mind is to make sure that the back of the box is about a foot higher than the front so that you can angle the lid and take advantage of as much sunlight during the winter and early spring.
Floating row covers: Floating row covers, often sold as Reemay or Agrofabric, are made of spun-bonded polyester or spun-bonded polypropylene. The fabric allows light, water, and air to move through but enables you to have 2-8° of frost protection. The row covers are available in a variety of weights but for frost protection, 0.5 ounces per square yard is the minimum requirement. Although the fabric is light enough to "float" over your plants, winter winds can cause abrasion so the cover should be supported with wire hoops or short stakes. To prevent the cover from blowing away, the ends should be weighed down with stones or buried right into the soil. Remember to leave enough slack to allow room for your plants to grow. The lifespan of the row cover is usually 2 seasons. When the fabric becomes a bit too ratty, use it to help germinate seeds. Placed over bare soil, row cover fabric acts as a mulch, keeping the soil moist and raising the soil temperature slightly. Seeds germinate very well in these conditions.
There are few points to keep in mind before deciding which method of season extension to choose.
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- Temperature differences - Plastic will raise temperatures much higher than row covers. While plastic is great for winter lettuce, cool season crops like cabbage and kale don't need such high temperatures.
- Materials - Not all plastics are alike. Make sure the material you use is UV treated and at least 3 mil. thick. Non-treated plastic will degrade and crack within just one season.
- Moisture - If you use glass or clear plastic over your plants, remember that water doesn't come through and they will need watering from time to time. Floating row covers don't have this problem.
- Ventilation - On sunny days in the early fall, it's easy for temperatures within cloches and cold frames to go up more than 20 degrees over ambient temperatures. Ventilation will not only keep temperatures moderate, but it will also help bring down humidity.