Jack Frost sneaks into our gardens every year whether or not we are prepared
for him, and some of our plants do not survive the visit. Frost occurs when
the air temperature drops below 32�F and ice crystals form on the leaves of
plants. Predicting his arrival, and mitigating its damage is possible.
The sky tells a lot about when frost is likely. Frost generally occurs when
the sky is calm and clear and afternoon temperatures are falling. Falling
temperatures coupled with a wind out of the northwest probably indicate the
impending arrival of a hard frost that will kill unprotected plants. If you
see clouds, however, take heart! They are the gardener's friends. While
the sun is out during the day it heats the earth, and after it sets, this
heat moves upward, which brings temperatures at the ground down. Clouds
that are forming and increasing indicate warmer temperatures. These clouds
will act like a blanket, keeping heat close to the earth and eliminating the
possibility of frost.
Breezes can also be good at keeping frost away. A breeze is something less
significant than the North Wind bearing down on your garden. Gentle wind
helps to keep the coldest air from sinking to the ground, which keeps the
air warmer around your plants.
Other, somewhat surprising, natural enemies of frost are moisture and
humidity. As moisture condenses out of humid air, a small amount of heat is
released. This little bit of heat may be enough to warm your plants and
prevent frost from forming on the leaves. Your soil should also be moist,
which will facilitate this process. Areas of your yard that have a lot of
mulch will likely frost first since the mulch prevents the moisture and heat
in the soil from escaping and warming the air around the plants.
In addition to keeping your garden moist you can also delay the arrival of
frost on your plants by locating your garden appropriately. Since
temperature drops about 3�F to 5�F with each 1,000-foot increase in
altitude, keep your garden off of the top of hills. And a garden in a
valley isn't smart either, since cold air tends to sink to the lowest
possible level, bringing frost to low-lying sections of your yard. The best
spot for your garden is on a rolling south-facing slope that is somehow
protected from north winds-maybe by buildings or trees. Planting your
garden near a body of water may also help to keep the air temperature warmer
and delay frost from forming.
Finally, you can stave off frost for a few nights by covering your plants to
retain moisture and heat near the leaves. You can use plastic tarps, burlap
bags, or bushel baskets. Almost any object will work. At some point,
however, frost will be as inevitable as winter following fall. Then all you
can do is to plan for next year.
Sources: Eliot Tozer; National Gardening Association