Frost Damage in the Fall Vegetable Garden

Seeing a crop through to harvest can be a challenge when frost is forecast.

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In this article you will learn about frost, hardiness of vegetables, what to do when frost is predicted, and how to evaluate post-frost damage.

What is Pala?

When water vapor freezes instead of condensing to form dew, we see ice crystals on the outer surfaces. It is called hoar, light or white frost. It forms when the air is moist and the ground temperature drops to 32°F or lower.

And because ground temperatures can be colder than air temperatures, it can form on soil even when the thermometer reads above freezing.

Frost damage occurs when ice crystals form inside vulnerable plant tissue, causing it to split open and robbing it of essential nutrients.

Photo by Matt Suwak

Conversely, when the temperature of both air and ground falls below the freezing point, and the air is dry, no visible frost forms. This is called hard or black frost or freeze.

Freeze dries out plant tissue – in fact, burns it.

understanding hardness

Vegetables vary, from being able to tolerate cold to being unable to tolerate even a light frost.

The degrees of hardiness in plants are described as:

hardy half-hardy tender very tender


When a vegetable is called “hardy,” it means it can withstand heavy frost and air temperatures below 28°F, according to James Myers, plant breeder and researcher at Oregon State University.

Hardy crops thrive in cool climates with three to six hours of sun per day. Planting time is in early spring or late summer. They react unfavorably to heat, often bolting — or going to seed — if temperatures rise.

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Examples of hardy vegetables include:

half hardy

Some vegetables are classified as “semi-hard”. They can tolerate one or more light frosts and temperatures in the 28-32°F range.

Semi-hardy crops also grow best in cooler climates, however, they need at least six hours of sun each day, also known as “full sun”.

Planting time is in late spring, just before the last frost date, or during the summer, in early fall to allow enough time for maturity.

Photo by Matt Suwak

And like hardy plants, they can bolt during heatwaves.

Examples of semi hard vegetables are:


Then there are the more delicate crops we call “tender”. They require temperatures above 32°F and can tolerate light frost.

The tender vegetables need eight hours of sun per day to thrive, and can’t be planted outside until the last average frost date has passed in spring.

Summer planting should be early enough to allow maturity before the first average frost date in autumn.

Examples of tender crops are:

very tender

Finally, there are “very tender” vegetables that require eight to 12 hours of sunlight per day. They cannot tolerate the formation of ice crystals to any extent, and should be planted after all risk of frost has passed.

The second summer crop should mature before the first average fall frost date.

Examples of very tender vegetables include:

Preparing for the Frost Event

Continue watering as the date of the first frost approaches, taking care to aim your hose at soil level near the roots, not above the foliage.

It is beneficial to water the plants during the day before frost is predicted. This allows your crops to absorb moisture, helping them to retain heat during the day and to generate heat through the evaporative process of transpiration.

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Harvest mature crops, as well as those that continue to ripen after ripening, like peppers and tomatoes.

Collect available seeds to save for the next year.

Mark the locations of plants, as the leaves of crops such as beets, garlic and radishes can become water-soaked, limp and unrecognizable.

The hardy types should be fine, and are likely to taste even better this time of year.

However, semi-hardy varieties may suffer, and tender and very tender plants may be lost.

Your best bet for maximum salvage is to shield all plants that are not hardy with covers, such as:

These can create an artificially warm “microclimate” of protection.

Some people swear by a thick layer of mulch, but the Farmers’ Almanac warns that it actually invites ice formation, trapping moisture and heat that would otherwise continue to warm the air around vegetation. Will be done.

Finally, when covering plants, be sure to firmly tie down the protective materials using bricks, rocks, or stakes to prevent them from blowing away in a strong wind.

Once you have taken the necessary precautions, all that remains is to wait.

post frost damage assessment

For many, the first frosty morning is invigorating, marking the definitive end of summer. But for latecomers to vegetable gardeners, it’s a time full of anxiety.

A bright vegetable garden may look beautiful at first glance. Harder crops, such as cabbage, may appear unchanged. However, the leaves of the tender type can be dark green and limp, similar to cooked spinach.

As the thaw begins, the damage becomes more apparent. It may take a day or two to become completely clear. All parts of the plant can be affected, from the leaves to the roots.

Damage may appear as:

Blistering Bruising Cracking Discoloration Foulness Shrinkage Slimy texture Softness Splitting Translucent Water saturation

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Evaluate the condition of each crop. You may be able to cut off the damaged parts and use the rest.

For example, although the outer leaves of a cabbage may be moist, the inner end may be fine. The florets in the center of the broccoli head may turn brown, but the rest of the head may look great. And very tender pumpkins may still be usable after the vines have died.

Plants that survive the frost usually continue to grow to maturity.

According to experts at Iowa State University Extension and Outreach, the notion that rhubarb stalks become toxic after a frost is an old wives’ tale. And while it is true that the inedible leaves contain “moderately toxic” oxalic acid, after frost, both the leaves and the petiole become so black and soggy, they don’t appeal to anyone anyway!

Facing Late-Season Challenges

Now that you understand the frost process, crop hardiness, protective measures and potential damage, you are ready to meet the challenges of late blight gardening.

Hardy plants are your best bet for resilience; However, the half-hard and soft types can survive even when covered.

If you’re a big fan of tender vegetables, you might consider building your own greenhouse to extend the growing season with ample weather protection.

It’s time to browse the latest seed catalogs and sketch out your best veggie garden!

Have you experienced crop damage due to frost in your garden? What are your favorite ways to protect your plants? Share your stories and questions in the comments below!

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Photos by Matt Suwak © Ask the Experts, LLC. All rights reserved. See our TOS for more details. Uncredited photos: Shutterstock.