Frost, Freeze, and Hard Freeze: What Every Gardener Should Know

As the chill of autumn settles in, it’s crucial to understand the differences between frost, freeze, and hard freeze to protect your precious plants. Here’s a quick breakdown:

Frost: The Sneaky Chill - Frost appears when water vapor in the air deposits as ice on solid surfaces. This typically happens when temperatures dip between 33°F and 36°F, especially with light winds. While frost may only cause minor damage, it’s important to note that if the air is dry or the winds are strong, frost can be unpredictable.

Freeze: The Serious Threat - A freeze occurs when temperatures drop to 32°F or lower. This can lead to significant damage for many unprotected plants, especially if the freeze lingers for several hours.

Hard Freeze: The Plant Killer - When temperatures plunge to 28°F or lower for a few hours, we experience a hard freeze. Unfortunately, this often means the end for many plants and seasonal vegetation.

Expert Insight: Mark Longstroth from Michigan State University Extension explains it clearly: “A frost is when you see a visible layer of ice, while a freeze is simply when temperatures drop below freezing.” Sometimes, you might even spot frost while the air remains above freezing due to colder surfaces, like your car or roof.

Special Cases

Black Frost: This occurs when temperatures drop low enough to freeze plants without visible frost. Frozen plants can take on a sad, water-soaked black appearance as they perish.

Wind Freeze: A cold air mass can sweep in, causing temperatures to plummet, even with winds at play.

Protect Your Plants! Want to give your garden the best chance to survive the upcoming frosty nights? Here are some simple steps you can take:

Cover Up: Use frost fabric, sheets, or plastic to shield your plants.

Water Wisely: Give your plants a drink with warm water to help them stay resilient.

Trickle Effect: Let water run at a gentle trickle for a few days to maintain moisture—just don’t overdo it!

Wrap Young Trees: Wrapping young tree trunks helps insulate them against cold temperatures, preventing freeze damage and maintaining healthier bark during harsh winter conditions.

Pots: To overwinter potted plants, move them indoors to a cool, bright location or use a cold frame for protection. Insulate pots with mulch or wraps, group them together for a microclimate, and remember to adjust your watering schedule to prevent rot during the colder months.

For specific timing, check the Idaho Average First Frost Date Map for accurate information tailored to your county.

By taking these steps, you can help your plants brave the chilly weather and thrive until spring returns. Protect your green friends, and enjoy a flourishing garden year-round!

Frost, Freeze, or Hard Frost? It's that time of year...!

 According to the National Weather Service, here are the definitions:

Frost:  Frost occurs when there is a solid deposition of water vapor from the air. Frost will form when solid surfaces are cooled below the dew point. An air temperature range of 33°- 36°, along with very light winds, is usually needed to initiate frost formation. At least minor damage is possible to plants. One must keep in mind that a frost is not guaranteed at these temperatures if moisture in the air is lacking and/or winds are strong.

Freeze:  Freeze occurs when the air temperature drops to 32°-or-lower. A freeze will result in significant damage to many unprotected plants, especially if the temperature remains at-or-below the freezing mark for several hours.

Hard Freeze:  Hard freeze occurs when the temperature reaches 28°-or-lower for at least a few hours. It usually means that many types of plants and most seasonal vegetation will be destroyed.

Mark Longstroth with Michigan State University Extension posted the following information explaining the differences more clearly than just a definition.

A frost is when we get a visible frost. A freeze is when the air temperature drops below freezing. Sometimes we get frost when the temperatures are above freezing and we often have a freeze without frost. It all has to do with the amount of water in the air.

At the dew point, water vapor in the air condenses on the ground and other surfaces as dew. If the dew point is below freezing, the water vapor condenses as ice, freezing as frost. So the air can be above freezing and the surface of your car (or the roof of your house) can be colder than the air and colder than freezing causing a frost even though the air temperature is above freezing. That is how we get a frost without a freeze. If the dew point is much below freezing then we can get freezing temperatures cold enough to freeze plants without any frost. This is also called a black frost, a freeze without a frost. When frozen plants thaw they have a water-soaked, black appearance as they die. Sometimes we get a freeze under windy conditions. This is caused by the movement of a cold air mass into the area with subfreezing temperatures. These freezes are called wind freezes.

Idaho Average First Frost Date Map will give you accurate information for your county.

Steps to take to help your plants survive as long as they can.

1.    Of course cover your plants with a frost fabric or sheets or plastic.

2.    Bring what plants you can indoors

3.    Water extra with warm water

4.    Keep water running at a trickle if possible for a few days.  Be careful not to over water.

5.    Wrap the trunks of young trees.

6.    Wrap pots that cannot be moved indoors.

Protect your plants!