Know Your Frost Types?image preview

Know Your Frost Types?

It’s fall and temperatures are dropping, which means frost is descending on much of the U.S. and Canada. Driveways are slippery, windshields need to be scraped, trees and grass will appear ghostly grey, and any garden plants that haven’t been harvested may be lost. There are many different types of frost—here’s a list of the types you might see on these chilly mornings and what they look like.

What Causes Frost?

Frost forms when the temperatures on surfaces, such as cars and trees, drop below freezing, causing water vapor to form into ice crystals. This happens most often on clear, cold nights, when there are no clouds to hold warmth in.

Here in Maine, we’ve already had a hard frost this third week of September 2020. Mid- to late-October is the most common time of the year for first frost dates across the United States. Florida has the latest frost dates of any state, with many areas seeing only a couple of days of frost per year, during the month of January.

See our frost dates with an interactive map here.

There are actually several different kinds of frost. Here’s a look at some common varieties:

Rime Frost

Rime frost looks like sugar sprinkled onto the edges of leaves and flower petals. It occurs whenever damp winds are coupled with extremely low temperatures. The word “rime” means “crust.”

Rime frost

Hoar Frost

Hoar frost is frost that resembles spiky hairs. This type of frost gets its name from the word “hoar,” which means “ancient,” because it resembles an old man’s bushy, white beard. It happens when water vapor freezes instantly after coming into contact with a very cold surface.

Hoar frost

Fern Frost

Fern frost is a kind of frost that appears on windows when there is very cold air on one side and moist air on the other. This causes tiny water droplets to form on the cold glass and freeze into patterns that resemble leaves or ferns.

Fern frost

Be sure to check out the Farmers’ Almanac’s list of average frost dates to keep track of frost to hit your area. And don’t miss these must-read tips on how to protect your garden from frost.

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RGE
RGE
2 months ago

No matter what kind of frost happens, we always call it Jack Frost.

Susan Higgins
2 months ago
Reply to  RGE

Yes!

ct0065
ct0065
7 years ago

When will colorado get first frost and first snow in denver metro area

Jaime McLeod
Jaime McLeod
7 years ago
Reply to  ct0065

ct0065 – Your average first frost is October 4. We predict light snow by the end of October.

Margaret Elaine Adams
Margaret Elaine Adams
8 years ago

It has been not to cold in Knox Indiana,
with lite on the snow.

Retired Drill Sergeant
Retired Drill Sergeant
10 years ago

First significant frost in Southeastern CT (New London County) was Sunday 10/10 32 degrees frost on grass, autos, etc.