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Season Extension - Starting Spring Seeds Early And Harvesting Late Winter Crops

Get Your Garden In Early and Start Reaping the Harvest Sooner


Steve Taylor / Getty Images

Don't let the frosts of winter or cold spring nights discourage you from growing vegetables. With some season extending tricks, you can start planting cold-weather crops right now and have your seedlings outdoors.

By warming the soil and protecting plants from wind, cold frames and other season extenders allow small farmers to extend the harvesting season as well as start plants earlier. On especially cold nights, cold frames can be blanketed with quilts, bedspreads or other thick blankets to further protect them. Even snow provides great insulation in deep winter.

Build A Cold Frame

Overwintering cold-hardy crops under cold frames leads to February and March harvests. If it's early spring and you don't have crops growing right now, you can still use cold frames to start your seedlings early outside.

A cold frame is basically a wooden frame set onto the ground with a glass top, called the "light," hinged on top. Gardeners often use old storm windows for lights. Lights are hinged onto the top of the frame so that they can be propped open for ventilation on warm, sunny days.

Build your cold frame in a few easy steps:

  • Find a top. Discarded shower doors or tempered glass patio doors are the best material for tops. You can also use storm windows, but they can break in strong winds.
  • Build your frame. Make the size of the frame match the size of your top. You can use scrap wood, untreated 2-by-4 or 2-by-6 pine finished with linseed oil, or, if you want to spend more money, cedar, redwood or composite plastic. Finish corners with steel brackets, or use a block of wood as an additional support, screwing each side into it.
  • Finish. Attach top to frame with any existing hinges on your door, or use new hinges to attach the two. If your garden is exposed to strong winds, sink a post near the top and use a hook and eye to keep the top propped open when necessary.

Build A Cold Frame

Build a Polytunnel

Mobile garden tunnels, often called polytunnels, are an inexpensive way to gain greenhouse-sized space for starting plants and extending your harvest season. Polytunnels have frames built of any number of strong, flexible materials: rebar, PVC pipe, fiberglass rods, and aluminum tubing are some. They can be covered with ultraviolet-resistant heavy greenhouse polythene, or plastic, that will last through at least a few seasons. Or, if budget is a concern, they can be covered in regular poly and recovered each year.

This is a basic outline of how a polytunnel is built:

  • Frame. Mark off a rectangle for your polytunnel. Sink pipe or PVC into the ground two feet apart (one foot in snow country) along the length of it to hold the hoops. Use 20-foot lengths of rebar, rebar covered in a PVC pipe, or PVC, and insert into one side of the pipe in the ground. Bend the 20-foot piece into a hoop and insert the other end into the opposite pipe.
  • End walls. Frame a door in wood. It's best if you leave space for a window at the top for ventilation. Staple the bottom of the frame to stakes in the ground and wire the top to the front hoop of the frame.
  • Plastic. Pull polythene from one side of the frame to the other, securing to the door frame in the end wall. Dig a trench (before you start) and bury each side of the plastic, or staple pipe ends to a 2-by-6 baseboard, then staple plastic to the baseboard with wood over that. Go side-to-side not end-to-end when pulling the plastic over the frame, and have some helpers - it makes it much, much easier. Another key tip: Do this on a calm day. Wind plus poly does not equal a fun time.

More on Polytunnels:

Build or Buy a Greenhouse

Of course, a greenhouse is the ultimate permanent growing space - more durable than a polytunnel and more extensive than a cold frame. Greenhouses are easier to insulate and protect from frosts than polytunnels.

On the negative side, greenhouses are more expensive by far than either a polytunnel or cold frame, and they are hard or impossible to move, so they're permanent structures for better or worse. This means that crop rotation becomes very important in the greenhouse.

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