Hold on to your plants! These Idaho cities are where Farmers’ Almanac predicts first frost

Shaun Goodwin, Alyse Messmer-Smith
·3 min read

The first day of fall arrived on Thursday, Sept. 22, so the first frost of the year is not far behind, potentially harming your hanging baskets and garden.

The Farmers’ Almanac has predicted the first frost in four of Idaho’s cities by finding the normal average first-frost date.

According to the almanac, the first frost will be hitting Boise on Oct. 8. The other three Idaho cities highlighted by Farmers’ Almanac — Idaho Falls, Moscow and Salmon — were all forecast to see their first frost on Sept. 20.

These dates are supposed to bring a light freeze between 29 to 32 degrees. Moscow hit 32 on Sept. 17, but Idaho Falls and Salmon are yet to hit the freezing point, in part because of a historically hot summer throughout the Gem State.

Temperatures in the 29-32 range will kill tender plants such as cucumbers, pumpkins and tomatoes, and have “little destructive effect” on other vegetation, according to the almanac.

Moderate freezes between 25 and 28 degrees bring heavy damage to blossoms, tender and semi-hardy plants and have a destructive effect on most vegetation. Severe freezes where it’s colder than 24 damage most plants, the almanac warns.

The Old Farmer’s Almanac, an almanac that started in 1792 and is annually updated, has predicted the first frost by city.

Here’s when the Old Farmer’s Almanac predicts your first frost by city in Boise:

Boise - Oct. 14

Bonner’s Ferry - Sept. 27

Coeur d’Alene - Oct. 12

Idaho Falls - Sept. 25

Lewiston - Oct. 18

McCall - Sept. 5

Mountain Home - Oct. 1

Payette - Oct. 14

Pocatello - Oct. 5

Rexburg - Sept. 18

Salmon - Sept. 18

Sandpoint - Sept. 22

Twin Falls - Oct. 3

How to protect your plants from frost

The Old Farmer’s Almanac also offers advice to keep your plants safe from frost damage and provides a list of each plant’s critical low temperature when frost will damage plants.

Carrots, peas and potato tubers have a critical temperature of 28-30 degrees, where they will begin to be damaged from frosty weather. Tomatoes, sweet corn, sweet potatoes and watermelon have critical temperatures starting at 32 degrees and are considered tender plants.

The Old Farmer’s Almanac advises you to cover your garden with row covers made of non-woven polyester or with bed sheets, drop cloths or medium-weight fabrics to protect them from frost.

Garnette Edwards, owner of Edwards Greenhouse in Boise, also recommended row covers or bed sheets.

“You do not want to cover (plants) with plastic,” Edwards previously told the Idaho Statesman. “Because it can build up the heat as the sun comes out underneath it, damage the foliage, and be just as detrimental as the frost.”

Edwards also recommends putting plants in a pot, pushing them up against the side of your house, and covering them due to the outside walls of the house providing some warmth and shelter from wind chill.

Here are a few ways you can prevent frost from damaging your plants and garden from Homes and Gardens:

  • Do not keep potted plants outdoors during the winter months.

  • Insulate your plants and garden with extra mulch before temperatures get colder.

  • Move your tender plants into a sheltered area.

  • Water plants in the mornings.

  • Wrap larger plants and planters to keep them warm if you cannot move them inside.