A guide to adding a hotbed that can provide plants with a constant soil temperature.
Are you thinking about a hotbed for your plants? I may be of help. A hotbed is nothing more than a coldframe supplied with some form of artificial heat. It is designed to maintain a constant soil temperature and to provide excellent facilities for the production of tender plants. In it, seeds may be sown so early that well-developed plants are ready to be set out several weeks ahead of those grown in coldframes. As the season advanes and not artificial heat is needed, the hotbed may be be used as a coldframe.
There are three methods of heating, the use of fermenting organic matter, steam pipes and elctric cables. Below I will discuss each one.
To make a hotbed with fermented organic matter, the bottom of the frame must be dug to a depth of three feet. In normal soil the earth sides will need no support, but in crumbly or sandy soil, boards, cement blocks or concrete must be used to prevent the sidewalls from caving in. Strawy horse manure which which has been turning and returned to process until heat is evenly distributed is used to bring the hole up to six inches below the round level. This process could take up to two weeks. You will spread the manure in even layers until you reach the top. Each layer must be well tramped, and after light watering the manure should be left two to three days to settle, then it will sit well. Six inches of good loam soil sould be added and carefully leveled. No planting should be done for two or three days, to allow full time for the soil to become evenly heated.
Now heating with steam pipes is practical only in connection with a greenhouse or house boiler.
This heating can be easily regulated. The sides of the frame must be of masonry consturction, and usually one coild of pipe fastened to the four sides is sufficient to heat.
The best and cheapest method of heating is by electric cables. Dig a hold one foot deep, then add six inches of cinders, then cover this with a light layer of coarse leaves to prevent the soil from sifting down. Leaves should be held in place by one inch of sand. An electric cable with a thermostate control can be purchased at any electrical supply store. The thermostate must be adjusted to register the temperatue of the soil, not of the air. The cable should be laid over the sand in long parallel coils, six inches apart, until the whole surface has been covered.
When it is in place one-half-inch of mesh wire should be laid over the cable. Over this five to six inches of loam soil are put in place and leveled.
In all of these three methods, heat is more even if insulation is provided. Soil should be banked evenly around all four sides of the frame to within a few inches of the sash. If this soil is well packed the only way in which cold air can reach the soil is through the glass top.
As you might already know the chief use of hotbeds is to raise early vegetables and annual plants. Seeds started in a hotbed will furnish plants three to four weeks earlier than those sown in a coldframe.
