Cold Frames and Hot Beds - Get a Jump on Spring
Cold frame greenhouses, cold frames, sun boxes, hotbeds -- call them what you will. All these small structures are designed to supply inexpensive and simple ways to extend your growing season. Once thought of as the poor man's greenhouse, these small growing boxes are a great addition to your garden, whether or not you have a full greenhouse. Let's have a look at the differences between these structures.
A cold frame, sometimes called a sun box, is probably the simplest one. It is an excellent place to acclimate greenhouse grown plants before you plant them out. This is basically a bottomless wooden box about 1 foot high either placed on the ground or sunk into the ground a few inches. The size is up to you, but make it a size so you can easily reach everything inside. If you want to plant directly into the frame, then add a 4 to 5 inch layer of topsoil and compost.
The most essential part of a cold frame is the slanting roof made of a transparent or semi-transparent material that will transmit heat from the sun. Old sash windows work well as covers, but you can use rigid or film plastic products. It is critical that the cover be movable and adjustable for ventilation. Both cold frames and sun boxes rely solely on the sun (that's why they're called sun boxes) for their heat so place them in a sunny sheltered spot, protected from wind.
In cold winter areas, use the cold frame for starting hardy annuals and early salad greens. It is also a good spot to harden off seedlings before they are planted in the garden. As the weather warms up, you can use it to root cuttings, to start tender annuals and even to germinate some seeds. Sow cold-weather crops in the frames in fall so you have a source of fresh greens and root crops in the winter months.
A hotbed is a cold frame with a source of heat inside it. It can be a thermostatically controlled electric heating cable, an incandescent light bulb or even manure! Any of these heating methods will keep plants from freezing even when outside temperatures dip to around 15F degrees.
To install a heating cable, dig out about 6 inches of soil and lay down the cable, looping it back and forth. Cover it with about 2 inches of sand and then 4 inches of topsoil. To use incandescent bulbs suspend eight 25 watt bulbs overhead, and connect them to a power source and a timer. To heat the hotbed with fresh manure, dig out an area below the frame to about 12 inches. Fill it with manure mixed with straw and then add 4 inches of soil on top. As the manure composts, it will emit heat!
A cold frame greenhouse is really a miniature greenhouse, and there are several kits on the market. They are generally taller than cold frames, standing up to 2 feet tall. They have a framework of wood, metal or rigid plastic, supporting sides of a semi-transparent polycarbonate plastic that is often double-walled for insulation. The roof is slanted and hinged, sometimes from the center so it can be accessed from either side. Durable, rigid and lightweight, they are easily moved around in the garden.
There are many different ways to extend the growing season and to provide a protected environment for your plants. Why not add a couple of cold frames or a cold frame greenhouse to your yard, and enjoy those early spring salads, fresh from your own garden
