When Is RI’s First Killing Frost: How To Extend Plant Life

RHODE ISLAND — Cooler overnight temperatures and the arrival of fall mean ornamental plants and produce gardens are short-lived in much of the country. The date to keep in mind in Rhode Island is Oct. 24.

That’s the average date of the first fall frost in Rhode Island, according to The Old Farmer’s Almanac. With its by-ZIP-code search tool, the publication makes it easy for gardeners to figure out when they’re most likely to start losing plants to frost.

In a light freeze of 29 to 32 degrees Fahrenheit, tender plants are killed. A moderate freeze, which occurs when temperatures dip to 25 to 28 degrees, causes more damage. Most garden plants can’t survive a severe freeze, which occurs at 24 degrees and colder, according to The Old Farmer’s Almanac.

This year was the fourth-hottest summer on record in the United States, and warm temperatures may stretch well into fall, according to the National Oceanic and Atmospheric Administration. The National Weather Service, an arm of NOAA, predicts a warmer-than-average fall in most of the country, including in Rhode Island.

That could give ornamental plants, especially, a few more weeks of life, but it’s always a good idea as the average date of Rhode Island's first killing frost approaches to keep an eye on local weather forecasts.

As the Oct. 24 approaches, Rhode Island gardeners should keep an eye on local weather forecasts and freeze advisories.

The average date of the first frost is an estimate based on historical climate data from the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. The probability of a frost occurring before the first frost date is around 30 percent.

You may be able to squeeze more life from plants by protecting them when overnight temperatures dip into the frost-danger zone. Some early fall favorites, such as pumpkins, tomatoes, sweet corn, watermelon and others, can be damaged at 33 degrees, according to the publication.

The best way to protect plants from frost is to cover them with a blanket, bedsheet or some type of row cover. Drape them loosely over the plants, and anchor them with bricks or rocks.

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If you know a frost is coming, harvest as many vegetables as possible. Tomatoes, cantaloupe and a few other fruits will continue to ripen after they’re picked, but others, like bell peppers or eggplants, can only mature on the vine.

The Old Farmer’s Almanac has more tips, as well as a vegetable-specific guide to frost dates.

If you invested in hibiscus and other tropical plants, Boston ferns, geraniums and others for your deck or patio, these ornamentals and herbs can overwinter inside. If you plan to do this, don’t wait for the first frost.

The Old Farmer’s Almanac spells out what to do — it depends on the variety of plant — but in general, give them as much light and humidity as possible, keep them away from heat ducts and expose them to artificial light if necessary.

Regardless of the plant, you’ll want to check for aphids and other insects. Spraying a 1 percent solution of Dawn dishwashing detergent (original) can do the trick. For best results, mix 2½ tablespoons of detergent in 1 gallon of water.

Bulbs, tubers and corms, such as cannas, dahlias and some lilies, can overwinter in the basement or garage. Just cut back the foliage, gently dig up the bulb and store the dried roots in a cool, dark spot, such as a basement.

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