Red Oak Leaf lettuce, January 2011
To many people, winter is a time of rest for the garden. The days are short, the soil is cool (or frozen), and there's a lot or rain falling or snow on the ground.
But to me, winter is the time of beginnings because my New Year's Eve is the winter solstice.
I live in the northern Oregon Willamette valley, and our winters here are pretty mild. Only short periods of freezing weather, and usually a fair amount of rain. On the shortest day, we get about 8 hours of sunlight. Not enough to keep things growing like they do in July, but it's enough to keep plants in maintenance mode or, on sunny days, even slowly growing. In my opinion, the biggest challenge I have in my gardens during the winter are cool soil and waterlogged soil.
Back in 2010, I started looking at ways to grow produce in my gardens during the winter. The problems that needed to be dealt with and mitigated were cool soils and too much water in the soils. I already knew that these issues could be solved by using greenhouses but I didn't have those, nor did I have the money to buy one.
So, the alternative was to look at something smaller. My research lead me to low tunnels, which are truly amazing devices. They are inexpensive, portable, easy to configure in any way that works for a particular garden bed. They can be used on the flat or over raised beds. Easy and fast to set up, and take down as well. In cold weather they can be covered with greenhouse film. In warm weather they can be covered with floating row cover fabric or shade cloth, depending on what you're growing and the time of year. They can be used to get a jump start on spring, and extend the season on the back end of the year.
Celery, planted in late January 2011. The kneeling boards down the center of the tunnel mean that the tunnel doesn't have to be opened other than the ends to allow entry and exit.
But care needs to be taken, as a low tunnel with greenhouse film on a sunny and warm day can also turn into an oven. I found that out when I first started working with low tunnels. I had 120 72-count nursery trays (aka plug trays) in a tunnel one day. The little seedlings had only been up for a few days and were looking good. One day it got up to the low to mid 60s, but I didn't think anything of it because it was cloudy. Then the sun came out. Working in the gardens, I enjoyed the sunshine for a couple of hours. And then I went to check on the seedlings.... The tunnel had been sealed, and when the clouds parted and the sun started shining that tunnel turned into an oven. It was probably between 90° and 100° in that tunnel. If the plants in the tunnel had been larger they probably would have survived. But still being in the cotyledon stage, they fried. I lost 8,642 plugs of seedlings in just 2 hours on that day.
Lesson learned. Now, if it's going to be over 55°, especially if there's a chance of the sun coming out, the least I do it to open the ends of the tunnels. But usually, if the highs are going to be in the mid 50s, the danger of freezing temperatures is probably over, so the greenhouse film may not even be necessary and the tunnels will have floating row cover fabric over them. If, for some reason, they do still have greenhouse film, I'll open the ends and roll up the sides during the day.
There are many ways to build low tunnels. My preferred style is bows made from 10' sticks of 3/4" schedule 40 PVC pipe over 5' wide beds. It's best to use schedule 40 PVC because it's more resistant to UV radiation and temperature fluctuations. A tunnel built with 10' sticks over a 5' wide bed will be approximately 40" tall, which gives the average person enough room to work in a closed tunnel when crawling down the center, and if working from the sides with the walls rolled up, the gardener only has to reach 30" (or less if you leave a center path.
Low tunnel set up for peas in February. The sides are anchored by blocks made of left over mortar (I'm a retired tile and stone installer).
I cover the tunnels with 12' wide greenhouse film or 12' wide floating row cover, which leaves one foot on either side for weights to anchor. Sand bags, rocks, soil, boards or other weights can be used to anchor the sides of a tunnel. Sand bags (or bags filled with soil) are the best weights to use as they are easy to move and won't damage film or fabric that flaps against them.
66" wide tunnel (that used to be my default width of beds). This tunnel's film is held down by boards. The ends of the tunnel are kept closed with pinch clamps that anchor the film to the end T-posts.
To anchor the bows of the tunnel, I use ground pins, a top rail, and T-posts. The ground pins are made from 4' round fiberglass rods normally used for moveable electric fencing. The rods can be cut with a side grinder using either a carborundum or diamond blade and the blade is used to shape the blunt end into a point, which makes driving it into the ground easier. Each rod is cut in half, making 2 2' ground pins. When driven into the ground to a depth of 12", they are sufficient to keep the bows in place. The ground pins are placed on either side of the bed at 5' intervals, and the pipe slid over them.
T-posts are driven into the ground at each end of the bed and the end bows are tied to them. A top rail of the same pipe that the bows are made of, is run down the center of the bows after they are installed, and anchored to the T-posts with string and the tops of the bows with duct tape. This makes a surprisingly sturdy frame to hold the film or fabric. I also like to lay plastic construction netting over the ridge pole and bows. This adds extra support to the film or fabric and helps to keep them from sagging when it's raining.
Low tunnel with netting on the sides and ends to keep chickens out of the tunnel when the film sides are raised.
All content and images, unless otherwise noted © Joanne Rigutto
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