Coldframe Gardening Now A Hotbed

This month, you can get a head start on spring by adding heating equipment to your cold frame. Any one of several methods of supplying heat will turn your hard frame into a hotbed.

A cold frame and a hotbed are constructed similarly but are set up and operated differently.

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Electricity is fast replacing the old-fashioned method of heating a cold frame with manure. However, a manure-heated hotbed involves a great deal of initial labor and has to be remade every season.

Once electrical equipment is installed in a cold frame, it lasts for years and is merely plugged into any convenient outlet when heat is needed.

Operating Electrically Heated Hotbed

An electrically heated hotbed is cleaner and easier to operate than the manure-heated frame, but the results are more specific since the heat may be controlled. 

The initial cost of installation is the most significant expense. The operation is inexpensive and can be made more efficient by good cold-frame 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. On the contrary, operation efficiency and conservation of electric current are best promoted by good practice.

Instructions for setting up an electrically heated hotbed, given below and at right, are based on a 6×6-foot frame covered with two standard 3×6-foot glazed cold frame sash. The heat is supplied by 60′ feet of electric soil-heating cable, available for heating this size frame.

A unit for a standard single-sash frame, or even a smaller one, may be obtained. A thermostat for controlling the heat is also available. 

Still, it is unnecessary 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.

Setting Up Frame

In setting up the frame, select a well-drained spot and dig a pit a foot deeper than the average surface level. This should extend a foot beyond the edge on all sides. 

Fill with 4″ inches of ashes or cinders to provide drainage and 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.

Instructions for installation usually accompany the heating cable, but the following hints are based on experience. 

Install the thermostat on the 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. The line is a single wire with both ends attached to the pin.

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″ inches between each circle.

The 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 Fahrenheit, 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 that 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 unique 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 conserve heat further.

As spring advances and the sun gets warmer, ventilation will be needed during the day. Keep the temperature as near 70° degrees Fahrenheit as possible by raising the sash to admit air.

Ventilate carefully, as a sudden burst of sunshine, even on a cold day, will send the temperature in a closed frame up to 100° degrees Fahrenheit in no time. 

To open the sash at this point would be fatal. Instead, spray the glass with cold water to lower the temperature, then ventilate.

Heating By Lights

Instead of burying the heating cable in the soil, the frame can also be 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 complicated; 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 of 4×4 feet, fasten a strip of wood lengthwise down the center of each strap. 

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 heat distribution, you can use four bulbs on each sash and four on the centerpiece, which divides the sash. A thermostat for heat control ensures safe operation.

The distance from the bulbs to the soil surface should not be 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. Some flower seeds, such as snapdragon, which require a long season of growth before flowering, can also be sown.

The facilities 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 3 to 4 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 cold frame.

Cabbage, broccoli, lettuce, leeks, and onions, sown towards the end of February, are less exacting in their requirements. These can be transplanted to a cold frame in three weeks, hardened off, and set outdoors in April in some sections and 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 exercises should be deep enough to permit the source covering.

A mere scratch is sufficient for tiny seeds. Space the seeds ⅛” to 14″ inches apart, depending on the size, press them into the soil and cover them.

Onions are best sown in flats which are transferred to a cold frame when the seeds have sprouted. Sow in rows 2″ inches apart and leave in the apartments until transplanted in the garden.

44659 by P. J. Mckenna