Frost is only weeks (days?) away in WNY; protect tender plants to prolong growing season

frostfog courtesy Donna Brok Garden Walk Garden Talk
Photo courtesy Donna Brok of Garden Walk Garden Talk

It’s just a matter of weeks (or perhaps days) before we get frost in Western New York.

Although he doesn’t know of any parts of Western New York that have gotten frost yet, there was a frost advisory Sunday night for the Town of Andover in Allegany County, said Mark Holt, Agriculture-Horticulture community educator for Cornell University Cooperative Extension of Allegany and Cattaraugus Counties.

That frost advisory prompted him to send along some tips on protecting tender plants from frost.

“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,” Holt said.

When will we get a frost?

When you can expect a frost depends on where in Western New York you live. Here’s a map from Cornell that shows when you might expect your first fall frost.

Holt also likes this chart that lists the probability of 36-degree, 32-degree and 28-degree temperatures on various dates, listed by town. Frost can occur even when the air temperature is above freezing, due to cold air settling, microclimate variations and other factors, Holt noted. Many frosts occur when the air temperature is in the mid-30s.

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. 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 because hot air is trapped closer to the earth’s surface.

What plants should I worry about?

Any house plants that were moved outside for the summer need to brought inside, Holt said. These are generally tropical in nature and won’t tolerate any kind of frost.

The other kinds of plants you should worry about are tender plants. These include flowering annuals that you want to enjoy a little longer, as well as warm-season vegetables such as tomatoes, squash and cucumbers. If you’ve got vegetables that are almost ripe, it’s nice if you can keep them growing a day or two longer.

The extent of damage to your plants from a frost 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), the duration of the frost and other factors.

A heavy (killing) frost can 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.

How can I protect my tender plants from frost?

Container Plants

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, Holt said. You can also sink the container into the ground or wrap both the plant and the container in burlap.

black milk jug retains heat during frost
Paint a used milk jug black and place it in the sun to absorb heat. Place the milk jug near your plant and cover the plant and milk jug. The milk jug will slowly release heat during the night, protecting your plant from frost. Photo by Connie Oswald Stofko

Plants in Garden Beds

Plants in beds can be covered.

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, Holt said.

Protective sheeting material is most effective when supported above the plants by some sort of a frame or even individual stakes. However, 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 because much of the stored heat from the day will be lost by dusk, he said.

After the frost has melted in the morning, remove the covers so the plants don’t overheat.

Grow tunnels can also prolong the growing season. Holt said he knows of someone in the eastern part of Cattaraugus County who was growing lettuce in a simple grow tunnel in January when the temperature outside was -20 Fahrenheit.

Bonus Tip: Add heat with milk jugs

Holt offered this tip, too, which I love.

Take empty milk jugs and paint them black. Fill them with water and place them where they can absorb heat from the sun.

Place the jugs near your plants. Cover the plants, along with the milk jug, before the sun sets. The jugs will slowly radiate heat during the night, and the protective cover will hold the heat in.

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