In the Garden:
New England
September, 2003
Regional Report

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Frosty mornings present wonderful photo opportunities.

Thwarting Frosts

Northeast gardens may be winding down but that doesn't mean Northeast gardeners are. I for one am not ready to say goodbye to the beautiful coleus, begonias, dahlias, and other tender flowers that have graced my garden all summer. Not to mention the peppers that are just reddening, and the tomato plants that are trying to feed the neighborhood.

With that in mind, I'm beginning to go into frost protection mode – dusting off frost covers and sheets that I'll drape over plants on cold nights, and relocating tender annuals in containers to warmer microclimates next to the house or the stone patio. Here are some strategies I use to help extend the gardening season, both spring and fall.

Avoid the Low Spots
The best place to locate a garden of tender annuals or borderline hardy perennials is midway down a south-facing slope. Just like water, cold air flows downhill, to the valleys or low spots where it settles and chills the plants. Hilltops and mountaintops also tend to be colder because of the altitude and wind exposure. So plants growing partially down a slope have the best chance of surviving frost.

If the slope faces south, even better, because there the soil receives more of the sun's warmth during the day and can radiate this heat at night, warming the air around plants. I live on the side of a hill, and frequently my garden remains frost-free when the low-lying fields along the river are covered with a white blanket.

Even if your garden is on a slope, if you have any kind of windbreak – trees, tall shrubs, a fence or other structure -- on the downhill side of the garden, this can trap the cold air around your plants and keep it from settling lower. Locate your garden where the cold air can move freely away from your plants.

Make the Most of Microclimates
I can grow borderline hardy plants by nestling them against a south-facing side of my house, along a stone wall, or bordering my stone patio. These structures absorb heat and keep the surrounding air temperature slightly warmer. I've had marginally hardy plants, such as lavender, survive next to the house yet die in the middle of the yard where they were exposed to winter winds and colder temperatures.

This approach doesn't work, however, with trees whose flowers are susceptible to early spring frosts, such as magnolias. Avoid growing these plants in south- or southeast-facing locations so these plants won't be fooled into budding too soon.

When Frost is Predicted
Sooner or later you'll be facing a clear night (no clouds to hold in the heat) with little wind (cold air can settle over the ground) and temperatures expected to drop near freezing. It's time to grab your plant blankets (plastic tarps, sheets, frost covers) and go out before dusk to cover your plants. Since you're trying to capture the warmed air that's radiating from the soil at night, make sure the protectors reach all the way to the ground so the warmed air can't escape. Anchor the bottoms with rocks or boards, and, if possible, prop up the protectors with tall stakes to prevent them from touching the foliage.

Humidity in the air can help prevent a frost because as the water vapor condenses during the night and forms dew on plants, some heat is released. This helps put the brakes on the drop in temperature. Without the moisture, the temperature drop is more rapid. To keep the odds in your favor, water your plants when a frost is predicted.

New Tools for "Frost-Sensitive" Gardeners
If you love tools, (or never catch the frost warnings in time), there's a frost-detecting gadget that can measure what's happening in your own backyard: a sling psychrometer. It helps you find the dew point – the point at which moisture condenses out of the air to form dew. Generally speaking, if the dew point is 40 or below, a frost is highly likely.

Here's a new use for an old product. According to researchers at the USDA Agricultural Research Service, a coating of kaolin clay on plant foliage can help prevent frost damage. This clay, which is commonly used in paint, pottery, and cosmetics, has been marketed in recent years as a foliar spray to prevent insect attack. Now it's been found to slow the freezing of water on leaf surfaces. It looks like a powdery coating but it washes off, and it's nontoxic. If you want to try it, spray it on your green tomatoes, which are more susceptible to chilling than the ripe ones!


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