The first day of fall arrived on Thursday, September 22, so the first frost of the year isn’t far behind, potentially damaging your hanging baskets and garden.
The Farmers’ Almanac 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 hit Boise on October 8. The other three Idaho cities highlighted by Farmers’ Almanac — Idaho Falls, Moscow and Salmon — were all set to see their first freeze on Sept. 20.
These dates are supposed to bring a light frost between 29 to 32 degrees. Moscow reached 32 on Sept. 17, but Idaho Falls and Salmon have yet to reach freezing point, in part due to a historically hot summer across the Gem State.
According to the almanac, temperatures between 29 and 32 degrees will kill tender plants such as cucumbers, pumpkins and tomatoes, and have “little destructive effect” on other vegetation.
Moderate frosts between 25 and 28 degrees cause heavy damage to flowers, tender and semi-hardy plants and have a destructive effect on most vegetation. Severe frosts where it’s colder than 24 degrees damage most plants, the almanac warns.
The Old Farmer’s Almanac, an almanac that began in 1792 and is updated annually, predicted the first frost per city.
Here’s when the Old Farmer’s Almanac predicts your first frost by city in Boise:
Boise – October 14
Bonner’s Ferry – September 27
Coeur d’Alene – Oct. 12
Idaho Falls – September 25
Lewiston – October 18
McCall – September 5
Mountain Home – October 1
Payette – October 14
Pocatello – October 5
Rexburg – September 18
Salmon – Sep 18
Sandpoint – September 22
Twin Falls – October 3
How to protect your plants from frost
The Old Farmer’s Almanac also offers tips for protecting your plants from frost damage and provides a list of each plant’s critical low temperatures when frost will damage plants.
Carrots, peas and potato tubers have a critical temperature of 28 to 30 degrees, where they will begin to suffer frost damage. 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 covering your garden with non-woven polyester blankets or medium-weight sheets, drop cloths or fabrics to protect them from freezing.
Garnette Edwards, owner of Edwards Greenhouse in Boise, also recommended bedspreads or sheets.
“You don’t want to cover (plants) with plastic,” Edwards previously told the Idaho statesman. “Because it can build up heat when the sun comes out below, damage foliage, and be just as damaging as frost.”
Edwards also recommends putting the plants in a pot, pushing them up against the side of your house, and covering them because the outside walls of the house provide some warmth and shelter from the wind chill.
Here are some ways to prevent frost damage to your plants and garden from Homes and Gardens:
Do not keep potted plants outside during the winter months.
Insulate your plants and garden with additional mulch before temperatures cool.
Move your tender plants to a sheltered location.
Water the plants in the morning.
Wrap tall plants and planters to keep them warm if you can’t move them indoors.