The Arrival of Jack Frost

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

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