Extending the Season by Rebecca Anderson



Christmas tree lights - warming and festive!

Cooler mornings have me thinking about fall, which will be here before we know it. With cabbages almost ready and tomato vines still covered with fruit in my garden, I'm planning for season extenders to give everything a few more weeks (hopefully!) to get the most out of my growing season.

Lots of different materials can be used as covers to extend the season.  The coverings must either be removed during the day or be clear enough to allow sunlight to pass through to warm the soil.  Sheets and blankets can work as long as they stay dry. If the fabric absorbs water, it will actually make the surrounding area colder as the water evaporates.  The sheets and blankets need to be removed during the day to allow sunlight to reach the plants and soil.  Floating row cover material is available from some nursery suppliers. It provides similar frost protection as a sheet but allows sunlight to pass through so it doesn't have to be removed every day.

I have raised beds for my garden, so I have tried a couple of different methods of "tunnel gardening."  With tunnel gardening, hoops are placed over the garden bed then plastic is stretched over the hoops to cover the plants.  Clear plastic with a thickness of 4-mil provides 3 to 6 degrees Fahrenheit frost protection.  The hoops have to be high enough that the plants don't touch the plastic because plants will freeze where they contact the plastic. There also needs to be a few holes cut in the plastic or it needs to be opened on warm sunny days to prevent overheating.  

Colorado State University has been studying ways to improve tunnel gardening. These include using space blankets on top of the plastic sheeting. The blankets are placed with the silver side toward the plants and will reflect 99% of the heat leaving the soil back toward the plants. This was protective even when temperatures dipped to 0 degrees F after a sunny day. Space blankets can be found wherever camping gear is sold.

Christmas tree lights have also been found to help extend the season.  Adding one string of 25 C-7 lights under the plastic sheeting can add up to 18 degrees F frost protection.  The lights are turned on at dusk and off at dawn. Christmas lights work better than a single bulb because they eliminate cold corners and edges. And in the case of frost protection, more is better.  Combining the plastic tunnel with Christmas lights and a space blanket gave up to 30 degrees of frost protection in CSU trials.  I think the lights would be a festive touch in the garden, too.

The CSU report about this research can be found at: http://www.cmg.colostate.edu/gardennotes/722.html.  I'll be doing a little trial of my own this fall and hopefully will have some success to report in a couple of months.