Landscaping & Nursery Information for Home Gardeners


The following methods can be used to limit frost injury. However, protection for temperatures below 25 degrees Fahrenheit may not be possible.

1. Sprinkling with water. It takes more cold energy for water to freeze. Maintaining a sprinkler running in the early spring may limit cold injury to strawberry flowers and tender transplants. Water in the fall can also limit cold injury.

2. Smudge pots. Pots generate localized heat. Small burning piles, where allowed, may provide similar effects. Check for dry grass and plant material nearby; even green plants may burn.

3. Fans. Still air cools faster than moving air. Cold settles; circulate air near the ground.

4. Covers. Old sheets, blankets and light rugs may limit cold injury to annual flowers and vegetables. Avoid plastic. Plastic will transfer the cold to the plant and provides little insulating capabilities. Leaving air spaces between plants and covers increases insulation. Avoid heavy materials which might damage plants or limbs.


Plant damage caused by frosts or freezes is the result of ice crystals forming within plant cells and the spaces between the cells. Crystals grow and rupture cell walls, similar to poking a hole in a water-filled balloon. The special "glue" holding cells together is destroyed; plants fail to maintain any shape.

Plants with bacteria, whether beneficial or destructive, inside cells are more prone to frost/freeze injury. Ice crystals form easily around the bacteria.

Plants suffering less frost/freeze damage, such as lettuce, bluegrass, cabbage and spinach, generally have a high salt concentration within cells and less water.

Many plants are capable of withstanding temperatures of 28 degrees Fahrenheit before significant damage occurs. This is particularly true of flower blooms on fruit trees in the spring.

Cold tolerance is a matter of plant genetics, growing conditions, and how fast/slow the temperature is lowered. Plants are able to withstand a gradual reduction in temperature with less injury than a rapid change.

See: Frost; Freeze


The average date of the last frost in Central Illinois is April 15. This doesn't mean it is a frost-free date. There is a 50 percent or less chance of frost on this date. The odds of a frost drop an additional 10 percent for each week past this date.

In central Illinois, the FROST FREE date is May 12. Add approximately 1 week for each 100-120 miles north of Springfield and subtract 1 week for each 100-120 miles south of Springfield.

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Frost may be expected when the night is clear, the stars brilliant, the air still and the thermometer  registers less than 45 degrees by nine o'clock. To protect plants cover them with weighted paper, burlap,  or light litter to check heat radiation; stir the soil  to fill the air with water vapor which, when it con-  denses as dew, raises the temperature more or less.  Spraying the plants and the ground is even better.  If the neighbors are distant enough not to be annoyed,  burn smudge fires of damp straw, weeds and similar  materials to fill the air with a cloud of steamy smoke.  In the morning shield the plants from direct sunshine.  If they seem frosted souse them with cold water to  "draw" the frost. 

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