A cold frame is a bottomless box with a glass top.
You place it over a part of your garden where crops already growing.
You can also put in young transplants or even direct seed in late summer.
Gardeners have been using cold frames for hundreds of years to extend their growing season beyond its normal limits.
A cold frame will give you several degrees of protection against cold weather.
Here are five things you can do to keep your plants safe from the colder temperatures of late fall and winter.

1. Surround the cold frame with bales of hay or bags of autumn leaves.
   Pile them up right next to the cold frame so the two are touching.
   This blocks drafts and helps keep out freezing winter winds.
   
2. Put an insulating cover over the glass top when the sun goes down.
   The glass top is the single biggest heat loss point in a cold frame.
   Even if you just put an old blanket or quilt over the top of the glass, it will stop a surprising amount of precious heat from being lost.
   
3. Pave the areas between your plants with small patio paving stones or bricks.
   The darker they are in color, the more effective they will be at absorbing heat.
   They absorb heat from the sun during the day and give it off at night, which warms the air around the plants.
   
4. Paint several empty gallon milk containers black.
   Fill them up with water and place them in the back corners of the cold frame and along its northern-most wall.
   Like rocks, they will absorb heat from the sun during daylight and give up their heat to the air of the cold frame when the sun goes down.
   
5. Install a heating cable in the soil beneath your plants.
   Do this before you plant anything.
   A soil heating cable is buried about eight inches below the surface and a protective screen is placed over the top of it.
   This helps the gardener avoid damaging the cable while cultivating the soil.
   Another way to heat up the soil is to bury fresh manure about a foot below the surface.
   

Depending on the severity of your winters, your cool weather crops will stay alive in the cold frame long into the winter months.
During the shortest part of the year they won't actually grow very much or very fast, but they will stay alive long enough for you to harvest them.
Who wouldn't want a freshly harvested vegetable for dinner during the coldest, darkest days of the year? Copyright Sharon Sweeny, 2009.
All rights reserved.