Budget Cold Frames

Looking to increase this year's planted crop? Here, University of Florida extension agent Tom Wichman demonstrates how to build a simple cold frame that will make it easy to get a few extra weeks of plant growth earlier and later in the year.

What it does:

• A cold frame speeds seed germination and protects plants from frost.

How it's built:

• The frame is a bottomless box, usually constructed from wood, with a slanted, tightly fitted top made of old windows or other transparent or translucent material such as plastic or fiberglass. A typical frame is approximately three feet wide and six feet long, with an 18-inch-high back that slopes down to 12 inches high in the front.
• The dimensions will depend upon the type of lid being used--an old storm window is ideal, but anything that lets light in and keeps cold air out will suffice. (If the lid is so light that it blows off, weigh it down with rocks or bricks.)
• If using scrap metal, the cold frame is a no-cost project.
• If new materials will be used, plan to spend about $30 to $40.
• Building a cold frame:
  1. Hammer four 2"x8"s together to make a bottomless box.
  2. Nail four more 2"x8"s together to make a second box. Set the second box on top of the first one.
  3. Nail a 1"x1" in an inside corner to hold the two sections together. Repeat in each corner. This step completes the building phase.

Where it goes:

• Place the frame outdoors.
• Put it over a garden bed or against the south wall of the house.
• Orient it so that it slopes to the south.

How it works:

• The sun warms the air and soil inside, creating a cozy environment for plants.
• Sow seeds for transplants directly in the cold frame. (Or, grow crops such as radishes, spinach, beets and lettuce to maturity in the frame.)
• Prop the top open during the day for ventilation and lower it at night to conserve heat.
• If the frame can't be checked regularly, consider purchasing a thermostatically controlled vent opener as insurance against cooking or freezing the plants.

Turn up the heat:

• For those who like the idea of a cold frame but want even greater temperature control, a hot bed is the perfect solution--it's essentially a cold frame with a heat source (commonly electric heating cable) to warm the soil.
• The cable includes a built-in thermostat preset for about 75 degrees Farenheit, ideal for germinating most seeds.
• Cable that features a thermostat and plug is sold by wattage and length.

Tips for growing:

• Although cold frames are simple to build, using them effectively isn't a fool-proof effort, because the hardest part is keeping them from overheating on a sunny day, which will severely wilt or even kill the plants inside.
• Be diligent about lifting the lid each morning as needed and putting it back on each night when the weather is chilly.
• In very cold parts of the country, it will be necessary to determine when winter-growing plants need the extra protection of a blanket thrown over the cold frame for the night.

Guests
Tom Wichman
Horticulturist, State Master Gardener Coordinator, University of Florida, Orange County Cooperative Extention Service
PO Box 110670
Gainesville, FL 32611-0670
Phone: 407-836-7573
Fax: 352-392-3870
Also in this Episode

Way to Grow : Episode WTG-211
•	Rare Native Plants
•	Budget Cold Frames
•	Unique Garden Containers
•	Healthy Gardening