The gardener in us dreads winter. We despair at the thought of losing our homegrown produce, not to mention the prospect of spending months indoors. Unfortunately that's exactly the situation that many find themselves experiencing. Between many states ordering people shelter in place and the unseasonably long cold weather that's endured all the way into May in some parts of the country, this is an instance where you may need to get creative in the garden and extend your growing season with one of these season extension techniques.
Cold frames are a simple, small-scale solution to season extension. They are easy to build and range in complexity from simple outdoor boxes to temperature-controlled, self-ventilating devices. Think of them as mini, unheated greenhouses.
There are a few principles to keep in mind regardless of the skill level required for your cold frame: angle, direction, depth, and materials.
Cold frames capture sunlight and protect plants from wind and freezing temperatures, rather like a greenhouse. For maximum light penetration, your cold frame needs at least a ten-degree angle. This slight slant makes a big difference for your plants.
The direction in which the slanted side of your cold frame faces also matters. You want your plants to have as much exposure to light as possible. Facing the cold frame south is the best scenario for plant growth as a southern exposure gets light all day. The next best option is west or southwest, followed by east and lastly north.
Think about the plants you want to grow in your cold frame. A very shallow cold frame won't allow enough room for your plants to grow. A good rule of thumb is to base the low end of the cold frame a few inches higher than the height of the crop at maturity. A basic cold frame is twelve inches at the low end and eighteen inches at the higher end. These measurements give an appropriate angle and allow enough room for plants to grow.
Light penetrates through clear materials like glass or plastic. These materials also trap heat, protecting plants from colder temperatures. Many gardeners build cold frames using old windows. It is also easy to construct a simple frame covered with greenhouse plastic.
Use the materials you have on hand to construct the box. Straw bales, scrap wood, bricks, or even cinder blocks all function as box materials. Just be sure the lid has a hinge so that you can open it on hot days for ventilation.
The ventilation process is vital. Your cold frame heats up on hot, sunny days, and temperatures can cook your plants well before dinner. For added security, place an outdoor thermometer in the cold frame to monitor temperatures.
Hoop houses are essentially large cold frames. The greenhouse grade plastic covering the metal hoops traps heat during the day to keep the plants warm at night. Unheated hoop houses are used to grow vegetables in climates as cold as Maine.
Building a Hoop House
Hoop houses are more complex to construct than cold frames. Do-it-yourself types find hundreds of plans online, many of them free. These plans are useful for first-time hoop house builders. Those less inclined to start from scratch often purchase hoop house kits. Kits are affordable and come in a range of sizes.
I personally prefer hoop houses large enough to stand in. During the winter, I enjoy gardening in my hoop house. The sun keeps temperatures in the fifties on sunny days, even when the mercury readings outside are below zero.
Hoop houses are not greenhouses. Unheated hoop houses derive their heat from the sun. On warm days, your hoop house heats up quickly. Keep a thermometer in the hoop house to monitor temperatures and ventilate on hot, sunny days. The best way to find out how much protection your hoop house provides is by keeping a record of temperature fluctuation. This helps you plan for next year.
In general, expect between four and eight degrees of protection inside your hoop house. For additional protection place row cover over the plants inside the hoop house. This provides an additional two to four degrees. As with cold frames, orient your hoop house to get the most sun during the winter months, keeping in mind the wind direction in your area.
Sometimes the protection offered by your hoop house and row cover is not enough. Placing a small space heater in your hoop house on really cold nights saves your vegetables from a chilly death.
Low tunnels, which are essentially small hoop houses, are easy to construct alternatives to hoop houses. Metal conduit hoops support heavy plastic or Agribon cloth over your garden beds. (These tunnels can also be installed inside hoop houses for additional protection). All you have to do to access your vegetables is lift the plastic along the side.
Container gardeners have a simple secret to extending the growing season: they bring their plants inside. Any home with a few bright windows, preferably windows facing south or west is suitable for container gardens. Start seeds all winter long for a continual, contained harvest.
Goodbye Winter Blues
It is time to change your attitude towards winter. Rather than tossing in your trowel, try one of these season extension techniques and enjoy fresh harvests late into the fall.