If you get serious about winter gardens, I suggest you see Eliot Coleman’s books, The New Organic Grower and Four-Season Harvest. He lives and farms organically in Harborside, Maine. His books are excellent sources for all the details about winter gardening. In the meantime, here are a few guidelines based on my knowledge and experience.
The basic concept is to mesh the technology of climate modification using mini-tunnels with the biology of the crops that are suitable. Of course you can get fancy with heating and lighting, etc and grow almost anything the year around. What I am referring to for our area simply allows you to grow a few cold-weather crops longer into the fall/winter and to start some spring crops earlier than normal. In this area, I have experience with lettuce, radishes, spinach, mache, onions, broccoli, carrots, and potatoes. I suggest you try some late fall sowing, under cover (described below and referred to as mini-tunnels) with these crops and then sow again in late January. You won’t need the tunnels in our climate until November. If you try to use them too early in the fall or too late in the spring, they will heat up too much with the plastic cover in place.
It is not difficult to set up a small bed for growing a few crops. Here is the design and system for a mini-tunnel that works in this area. Supplies needed to make a 4x25-foot bed include:
1. 6 mil clear plastic. It comes in 10 and 20-foot wide strips. I buy it in a 100-foot roll.
2. 18 reinforcing rods, each piece 24 inches long, 3/8-inch diameter.
3. 9 pieces of ¾- inch (inside diameter) plastic tubing, each piece 7.0 feet long. You can buy it in rolls and cut it. This 7.0-foot length of tubing is designed for a bed that is 4 feet in width.
4. Boards, bricks, rocks, and straw to hold down the plastic. Maintaining the tunnel in strong winds is the biggest problem, and anchoring the plastic is the key.
5. Optional, but very desirable: Heat absorbing material inside the tunnel. I use one-gallon glass and plastic jugs, painted black, and filled with paramagnetic rock. It works great. The jugs pick up a lot of heat during the sunny days and dissipate it into the soil and tunnel at night. Set the jugs a couple inches deep into the soil. I use about 15 jugs for my 100-square foot garden bed. The magnetic energy absorbed by the paramagnetic rock is also used by the plants for increased growth.
The construction is easy:
1. Lay out exactly where the 18 reinforcing rods will be placed. Use a string to line them up on each side of the bed. Be sure they are the same distance apart across the beds. Try for 4-foot spacing. Pound the reinforcing rods about 18 inches deep into the soil on each side of the beds. That leaves about 6 inches sticking out to “hook” the plastic tubes. 3-foot spacing of the rods, along the sides of the bed works fine.
2. Place the 7.0-foot plastic tubes over the rods, to make the semi-circle frame.
3. Adjust the tubes so you have a uniform height and shape for all the tubes. This will help to provide a uniform surface with the plastic cover.
4. Cut the 10-foot wide plastic to desired length. Allow about 5 extra feet on each end for good anchoring.
5. If you are doing this alone, choose a calm day to install the plastic. Lay the plastic over the tubes. Anchor the windward side so that no wind can get under the plastic! This is important! First lay down some boards, bricks, rocks, etc. on the plastic. 2x6 planks work very well. Then cover that all up with a heavy layer of mulch or straw (wood chips are fine). Don’t leave any place for the wind to get under the plastic. Anchor the ends in a similar manner.
6. Remember that you are going to periodically open this up to work in the garden bed. So on the lee side (East, if you have N-S rows), I just anchor the plastic with 2x6 planks, weighed down with a few cement blocks. It works well to have a 4-6-inch layer of straw down in the pathway on the lee (east) side also. It will help in the winter when the soil is wet and you want to open the tunnel.
According to Eliot Coleman, a tunnel of this type will effectively move you to a climate that is about 1.5 hardiness zones to the south. For us that means a climate like mid-Louisiana. The real advantage is the ability to get started at least a month earlier in the spring. I use the mini-tunnel to start early seeds for lettuce, spinach, onions, cabbage, broccoli, and tomatoes. Some of the plants can be left in the tunnel and others can be transplanted to other beds when the time is appropriate.