Coldframe gardening allows you to get a head start on spring by adding heating equipment to your coldframe this month. Any one of several methods of supplying heat will turn your coldframe into a hotbed.
Both a coldframe and a hotbed are constructed in the same way but they are set up and operated differently.
Electricity fast replaced the old-fashioned method of heating a cold-frame with manure. A manure-heated hotbed involved a great deal of initial labor and had to be remade every season. Once electrical equipment like a soil heating cable is installed in a coldframe, it lasts for years and is merely plugged into any convenient outlet when heat is needed.
An electrically heated hotbed is not only cleaner and easier to operate than the old-fashion manure-heated frame but the results are more certain since the heat may be controlled. The initial cost of installation is the largest expense. Actual operation is not expensive and can be made more efficient by good cold frame plan and construction.
The general advice that good results are obtained when the heating cable is merely placed on the soil surface without any preliminary preparation, is not borne out by my experience. Operation efficiency and conservation of electric current are best promoted by good preparation. Instructions for setting up an electrically heated hotbed, given below and at right, are based on a 6 x 6-foot frame covered with two standard 3 x 6-foot glazed coldframe sash. The heat is supplied by 60 feet of electric soil-heating cable, available as a unit for heating this size frame. A unit for a standard single-sash frame, or even for a smaller one, may be obtained. A thermostat for controlling the heat is also available but is not necessary if the apparatus is disconnected by a switch when the desired temperature is reached and again connected when it has fallen. This, of course, requires constant attention.
Cold Frame Set Up – DIY
In setting up the frame, select a well drained spot and dig a pit a foot deeper than the normal surface level. This should extend a foot beyond the frame on all sides. Fill with 4 inches of ashes or cinders to provide drainage and to prevent heat from escaping into the surrounding soil. On top of the fill, inside the frame, spread an inch of sand to help distribute the heat. The cable is placed on top of the sand.
The heating cable is usually accompanied by a set of instructions for installation hut the following hints are based on actual experience. Install the thermostat on the inside rear wall of the frame near the left-hand corner as you face it. Insert the plug of the heating cable and separate the wires leading from it. Actually, the cable is a single wire with both ends attached to the plug.
Starting from the plug, lay one wire along the side wall, curve and run it parallel to the front wall. Then loop back and forth until the entire cable is used up. The final loop should run parallel to the rear wall and end at the plug. To get an even distribution of heat, the single wire should run along the three sides of the frame at a distance of 4 inches from the wall; the looped wire should be 4 inches from the right wall at the loops, 4 inches from the initial straight wire on the left side and 7 incites between each loop.
Wire mesh should be placed on top of the cable to prevent any injuries from garden operations. On top of the wire place another inch of sand followed by 6 inches of prepared soil. The hotbed is now ready for use.
If a thermostat is used set it at 65 degrees the temperature most suitable for the general run of seeds and cuttings for which the hotbed is designed. Attached to the thermostat is a sensitive brass tube which is partially buried in the soil. This controls the soil temperature. Since the air temperature within the frame on cold nights and cold, cloudy days would be lower than the soil temperature, it is necessary to cover the sash with sacking, hay, straw or special mats made for this purpose to keep the heat within the frame. The sides of the frame should also be mounded up with manure, leaves or soil to further conserve heat.
As spring advances and the sun gets warmer, ventilation will be needed during the day. Keep the temperature as near 70? as possible by raising the sash to admit air. Ventilate carefully, however, as a sudden burst of sunshine. even on a cold day, will send the temperature in a closed frame up to 100? in no time. To open the sash at this point would be fatal. Spray the glass with cold water to lower the temperature, then ventilate.
Heating by Lights
Instead of burying heating cable in the soil, the frame can also he heated by electric light bulbs attached to the interior of the glass sash. Even though this method has its limitations, it may be superior to cable for raising seedlings but not for rooting cuttings, which require bottom heat.
Installation is not difficult; you can use the standard 3×6-foot sash or the smaller 2×4-foot Zephyr sash. Using two frames of the latter, or an area 4×4 feet, fasten a strip of wood lengthwise down the center of each sash. Six regular porcelain bulb sockets are wired and attached to each strip. Heat is supplied by 12 Mazda B 25-watt frosted bulbs, six on each sash.
For more even distribution of heat, you can use four bulbs on each sash and four on the center piece which divides the sash. A thermostat for heat control insures safe operation. The distance from the bulbs to the soil surface should not he less than 15 inches. These frames, too. will need the outside covering on cold nights to conserve heat.
Hotbed Operation
Some vegetables can be started in the hotbed in February to provide plants for early crops. A few kinds of flower seeds such as snapdragon, which require a long season of growth before flowering, can also be sown. The facilities you have available for handling the seedlings and plants later should govern your selection and the quantity of material started in the frame. Tomatoes, eggplant and peppers sown in mid-February would need transplanting three to four weeks later. Heat would still be needed. However, if the seedlings are sown thinly and later thinned to 4 inches apart, they can remain in the hotbed until about April 1 when they should be potted up and placed in a protected coldframe.
Cabbage, broccoli, lettuce, leeks and onions, sown towards the end of February, are less exacting in their requirements. These can be transplanted to a coldframe in three weeks, hardened off and set outdoors in April in some sections, later in others. Here the time for starting such seeds will depend on the planting-out time, although these crops can stand lots of cold without damage. Seeds are sown in drills 3 inches apart; the drills should be just deep enough to permit covering the seed. A mere scratch is sufficient for very small seeds. Space the seeds 1/8 to 14 inch apart, depending on the size, press into the soil and cover.
Onions are best sown in flats which are transferred to a coldframe when the seeds have sprouted. Sow in rows 2 inches apart and leave in the flats until transplanted out in the garden.
