Mark Holt, Community Educator, Agriculture/Horticulture
Cornell University Cooperative Extension of Allegany and Cattaraugus Counties
Historical data from the National Weather Service indicates that many areas of Allegany and Cattaraugus Counties will have their first frost of the season within the next two weeks. While it’s sad to see the traditional gardening season come to an end, you may be able to extend your gardening season a bit longer with careful attention to the weather forecast and a little extra work to protect tender plants.
Frost forms first in low-lying areas. Cold air is denser than warm air, so the colder air settles in low-lying areas of your landscape and garden. Tender plants in these areas need protection to survive frosts. Sloping areas tend to frost less often, as it is more difficult for the cold air to settle there.
As air cools, moisture condenses out of it and settles as dew. When the temperature of plant surfaces falls to 32 degrees, dew will freeze and frost will form on the plant. Frost is more likely to form on cloudless nights without wind. A cloudy night tends to stay a bit warmer, as hot air is trapped closer to the earth’s surface.
Tender plants such as annuals and warm season vegetables are subject to frost damage. A heavy (killing) frost can even kill these non-hardy plants. Frost damage or death occurs when the moisture in the plant cells freezes and damages the cell walls. When the plant thaws, the damaged cells lose their ability to support the plant and transport water and nutrients.
Frost can occur even when the air temperature is above freezing, due to cold air settling, microclimate variations, and other factors. Many frosts occur when the air temperature is in the mid-30s. The extent of damage to your plants will depend on the type and hardiness of the plant, the maturity of the plant (older plant tissue is less subject to freeze damage than newer tissue), duration of the frost, and other factors.
To protect from frost damage, cover your plants. If plants are in containers, move them into a protected area or indoors. You can cover individual plants or a whole row of plants with burlap, bed sheets, plastic sheets, milk jugs, inverted flower pots, or anything else that will preserve stored heat and prevent dew from settling on the plants. Protective sheeting material is most effective when supported above the plants by some sort of a frame or even individual stakes. But if necessary, it can be laid directly on the plants and still provide some protection. Even the spun polyester “floating row covers” available at garden centers can offer 4-5 degrees of protection against freezing temperatures and frost.
Remember to cover your plants before nightfall, as much of the stored heat from the day will be lost by dusk. After the frost has melted in the morning, remove the covers so the plants don’t overheat. You can collect extra heat during the day by painting empty milk jugs black and filling them with water. Place them near the plants in your garden. The jugs will slowly radiate heat during the night under the protective cover.
Container plants are particularly susceptible to frost damage because their root systems are limited and the above-ground container is exposed to rapidly fluctuating air temperatures. Move container plants indoors or into a protected area, or sink the container into the ground, or wrap both the plant and the container in burlap to protect from freezing temperatures.
Further information on this and other gardening topics is available from Cornell Cooperative Extension Master Gardener Volunteers in Allegany and Cattaraugus Counties. Contact a Master Gardener by telephone or e-mail:
Allegany County: (585) 268-7644 x23, e-mail: email@example.com
Cattaraugus County: (716) 699-2377 x127, e-mail: firstname.lastname@example.org