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Behind the Forecast: Helping plants recover after a frost

Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.
Updated: Apr. 23, 2021 at 10:00 AM EDT
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Protect your spring flowers during frost advisory (Source: WOIO)
Protect your spring flowers during frost advisory (Source: WOIO)

LOUISVILLE, Ky. (WAVE) - After a stretch of warm Spring weather, Winter made a quick comeback. For those who’ve already planted or had their annuals bloom the question now is, how do I help my plants recover?

One of the most common types of environmental plant injuries is freeze injury, according to Fine Gardening.

Many woody plants prepare for winter by dropping their leaves, causing their branches and trunks to start losing water. The water loss causes the plant cells to have higher concentrations of sugars, salts, and other organic compounds, according to EarthSky. All of this lowers the plant’s tissues’ and cells’ freezing point, helping them to survive through a frigid winter. Unfortunately, there are limits to how much cold a plant can withstand.

Some plants can make their own kind of antifreeze. By keeping a water a liquid in temperatures as cold as -40°F, some plants can use supercooling to survive in harsh conditions.

In the spring, new leaf growth pumps water back into a plant, reducing its shield from the cold.

The contents of a plant’s cell are surrounded by a rigid cell wall and a cell membrane. When a plant experiences sub-freezing temperatures, ice can form in between the cells and inside the cells themselves. While ice between the cells won’t cause significant harm to the plant, ice within the cells injuring special cell structures, potentially rupturing the cells, and damaging the plant.

Evidence of freeze damage depends on the plant. Some plants may look shriveled while others may turn brown or purple. The stems of some plants may even split open. It may take days or weeks for the full extent of the damage to be evident.

Using the “bend test,” is another way to learn if a plant’s limb is dead. If you can bend a limb and it doesn’t break then the limb is still healthy. Also, if you see moisture coming out of the branches or the bark of a tree, that’s a sure sign that the plant has been damaged.

Experts recommend removing anything “soft” or “mushy.” It’s also recommended to wait until new growth is seen before pruning damaged branches. For woody plants, scratch the bark on the stems; if you see green underneath that branch is still alive.

Plant parents are advised to water plants to help them recover from the trauma of cold weather. When plants freeze, moisture is sucked from their tissues and cells. Watering plants enables them to rehydrate.

Did you forget to bring a potted plant inside during the cold? Bring them inside anyway, avoiding rooms that are very warm and direct sunlight. Experts say that eventually, the dead parts will fall off.

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