Find out what you can do to help plants recover from frost damage.
How to Save Frost-Damaged Plants
The plan of action for frost-damaged plants can be summarized in three words: Wait, see, and water. Since not all frost damage is obvious immediately, waiting is the best approach. What you shouldn’t do is reach for the pruners and cut off the damaged plant parts. The more pruning you do, the more energy the plant needs to heal those wounds instead of spending it on recovering. The same applies to fertilizing. A nutrient boost in the fall as the temperatures gradually drop does more harm than good. It coaxes the plant into developing new growth that is vulnerable to cold damage. Watering is the only thing that can help your plants recover but make sure not to overwater. If the frost damage is on plants that you should have brought indoors for protection, move them right away to their overwintering location. Give the plant a week or two to see if any plant parts have sustained permanent damage. If it’s mostly foliage, flowers, or buds, dead ones will shrivel up on their own and you can remove them. Otherwise, continue giving the plant its usual winter care. Some annual plants can be overwintered indoors but for most tender annuals as well as vegetables such as tomatoes and peppers, there is not much you can do to save them. Provided that you have planted perennials, trees, and shrubs suitable for your hardiness zone, you don’t need to worry about saving them. The collapsed and yellowing foliage of a lily after a frost is part of its natural process of entering dormancy, It will bounce back to life in the spring.
How Frost Harms Plants
Plants get damaged by frost when the fluid inside individual plant cells freezes and forms ice crystals which rupture the cell walls. As a result, the fluid drains from the cells. In order to understand how plants are affected by frost, it is important to know there is a difference between frost and freeze. Frost is visible, it’s the white icy layer on the lawn in the morning. Frost can occur, but doesn’t always, when there is a freeze and the air temperature drops below 32 degrees Fahrenheit. In low relative humidity, plants can be damaged by freezing temperatures without any signs of frost. Frost can happen even if the air temperatures are above freezing as long as the relative humidity of the air is high. In those conditions, the surface temperature of plants and other inanimate objects drops below freezing, causing ice crystals form. Not all plants are equally vulnerable to frost. Tropical plants have a genetic makeup for warm climate only and are the least protected against freezing cold. Even for hardier plants, maturity and health are significant factors. Generally, well-established plants tolerate lower temperatures better than young, more tender plants. That’s why many tender seedlings should never be transplanted in the garden until after the last frost in the spring. Also, not all frost is created equal and does the same damage to plants. Frost happens during the coldest time of the day, just before daybreak. The longer it lasts, the higher the risk for plants. A short cold snap is less likely to cause damage than one that lasts for several hours. Plantings on south- or west-facing slopes are less prone to frost damage because of the residual heat that these areas get during the day, which protects them during nighttime frosts.
Identifying Frost Damage on Plants
You will likely notice first signs of damage more clearly the day after a frost on the most exposed plant parts and those with the softest tissues. Leaves, new shoots, and buds turn limp, dry, distorted and yellow, brown, or black in color. Flowers wilt and shrivel. Tougher stems are less likely to get hit although they can also succumb in a strong, long-lasting frost.
How to Prevent Frost Damage
The best thing, of course, is to prevent frost damage before it occurs. Abstaining from any late fertilizing and pruning are important steps. New growth, whether it has been triggered by fertilizer or pruning, is especially vulnerable to frost damage. Make sure to always choose plants that fit your USDA zone. Any plants that are not hardy enough need to be grown in containers and brought inside, or moved to a warmer, protected location, before the first frost. If you are still picking tomatoes, peppers, and other warm-season crops when fall frost hits, you can temporarily protect the plants with bubble wrap to extend their life until harvest is over, though a protective row cover would serve you better in the long term.
