How To Build: COLD/HOT FRAME FOR GARDENING
- A cold frame is one of the old standby garden tools. It’s great for extending your garden season,
but it’s not just for use in colder climates. It can help you get those seedlings in before the
hot weather hits.
- A cold frame is a raised bed vegetable garden that has a covering over it.
Its primary use is to put seedlings outside before they may be ready to go, especially
tender crops that absolutely can’t take a freeze, like tomatoes and peppers.
It encourages “hardening off” of seedlings, which gradually acclimates the plants
to the temperature swings.
- While this seems natural for some of the colder states, it’s actually good for use
almost anywhere. In the South, the summers are so hot that many crops like tomatoes
don’t have enough of a temperate growing season to do well, so getting an early start
may be the only way that some of these can be grown.
- A cold frame just has a transparent cover, it could be a clear polyethylene cover , or simply a discarded window or
screen door with the glass insert.
- A cold frame usually has a slope to the top of the frame, and it’s best to have the
low side facing south to capture as much of the sun as possible. On the northern side
you may want to add a windbreak, or place it on the south side of a building. Even a
few bales of hay can keep the cold northern winds out of the box. Just be careful to
make sure that it has full sun.
- You can make your own cold frame from scrap lumber. Since its primary purpose it to
act as an insulating container, be sure to take care and make it as tightly sealed
as possible. Weatherstripping is a must. If you are using a window or door for the top,
you may want to size the box to it to ensure a good fit. If you are using a clear
polyethylene for the top, make it a thicker type to improve the insulation. You may want
to make the sidewalls from at least 2 inch lumber (or thicker) to keep the cold at bay.
- Commercial cold frames are made from both wood and poly, and have both glass and poly covers.
These come in small sizes that are simply for starting seedlings, while others are large
enough to cover a full sized bed and the cover is simply removed when the threat of freezing
temperatures has gone.
- Finally, another use for a cold frame is to help plants overwinter in extreme conditions.
Perennial plants can get that extra bit of winter warmth to get them through when covered
with a cold frame.
- Hot beds and cold frames are used by gardeners for propagating vegetables, flowers and ornamentals.
Hot beds are used for starting the plants and cold frames for hardening plants
to outdoor conditions before transplanting.
For most home gardeners the same frame can serve both purposes. The principle difference between the
two is that hot beds have a heat source.
Present-day frames are often completely above
ground and plastic covered.
- Although steam, hot water and even manure have been used to heat hotbeds,
most home gardeners use electric cables. A thermostat is needed to control the
temperature in the bed. Although heating cables operate on either 240 or 120 volts,
most small beds of 10 feet or less can be satisfactorily operated on a 120 volt system.
One 60 footcable is required for a 6 x 6 foot bed and two 60 foot cables for a 6 x 12 foot bed.
The cables should be arranged in the beds. Heating cables and thermostats are available from mail order
and garden supply centers.
- A soil temperature of 70 to 75 degrees F is ideal for germination of most seeds.
Following germination, adjust the temperature to suit the particular plant.
- Cool-season crops such as lettuce, cabbage and cauliflower require an air
temperature during the day of 60 to 65 degrees F. Warm-season crops such as tomatoes,
peppers, and melons require an air temperature of 65 to 75 degrees F.
- Night temperatures are usually 5 to 10 degrees F lower than day air temperatures.
If the air temperature in the bed goes above 85 degrees F, ventilation will be necessary.
The beds usually require ventilation on all mild, sunny days. Electrically-heated beds
tend to dry the medium rapidly, and attention to watering is a must. The soil should be
kept moist at all times but not wet. Apply water in the morning so the plant foliage will dry before evening.