Gardening Articles: Flowers :: Annuals
A Gardener's Guide to Frost (page 2 of 3)
by Eliot Tozer
5. Scrutinize the Soil
Your garden's soil type can affect the amount of moisture it holds and the plants' ability to withstand cold weather. Deep, loose, heavy, fertile soil releases more moisture into the surrounding air than thin, sandy, or nutrient-poor soil. The more humid the air, the higher the dew point and the less likely that frost will form on those plants. Heavily mulched plants are more likely to be frosted, since mulch prevents moisture and heat in the soil from escaping and warming the surrounding air. (Light-colored mulches such as hay or straw have the additional disadvantage of reflecting sunlight and heat during the day.)
6. Know Your Plants
The plant itself determines the likelihood of frost damage. Immature plants still sporting new growth into the fall are most susceptible -- especially the new growth. Frost tolerance tends to be higher in plants with maroon or bronze leaves, because such leaves absorb and retain heat. Downy- or hairy-leaved plants also retain heat and reduce wind-drying of the leaves. Compact plants expose a smaller proportion of their leaves to cold and drying winds. By the same token, closely spaced plants protect each other.
What's a Gardener To Do?
So you've checked the weather conditions and decide that, yes, Jack Frost is coming and protecting your plants is worthwhile. You'll want to do two things: First, cover your plants, both to retain as much soil heat and moisture as possible and to protect them against strong winds, which can hasten drying and cooling. Use almost anything to cover plants: newspapers, bushel baskets, plastic tarps, straw, or pine boughs. Spun-bonded fabric row covers will protect plants down to 30°F, polyethylene row covers to 28°F. Cover the whole plant before sunset to trap any remaining heat. Lightweight coverings such as row covers and newspaper should be anchored to prevent them from blowing away.
Second, keep the soil moist by watering your plants the day the frost is predicted. Commercial fruit and vegetable growers even leave sprinklers on all night to cover plants with water. As the water freezes, it releases heat, protecting the plants, even though they're covered in ice. To prevent damage, the sprinklers need to run continuously as long as temperatures remain below freezing.
And as you survey your garden's fading glory, you may take heart from the experience of John Loudon, a 19th-century British horticulturist. Loudon stuck four stakes into a plot of grass to support a cambric handkerchief 6 inches above the surface and found that the temperature beneath it remained 9°F warmer than the temperature of the surrounding air. Yes, you can beat the frost -- at least for a few nights.