The date of the first frost varies in each US hardiness zone. Some experience it as early as September and others as late as December. If you didn’t bring in your plants on time, a couple of them may have gotten frost on them that shouldn’t have but, is it safe to wash frost off your plants the following day?
As a whole, it is ill-advised to wash frost off plants. The temperature difference from the water causes the ice crystals in the cell tissues to thaw too quickly. For tender plants, this leads to cell wall damage. For cold-hardy plants, it forces them to resume normal internal functions too soon.
Below, I elaborate more on this problematic practice with a better alternative to “defrost” your plants:
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Table of contents
Why Should You Not Wash Frost Off Your Plants?
- The plant goes into thermal shock from the temperature spike.
Adding a burst of water speeds up the melting process of the frozen cell walls, absorbing heat from the temperature difference. This signals the plant to perform its everyday activities as if the weather has warmed up already. Depending on the cold-hardy plant, they can probably adapt and handle the shift in temperature provided they have been “hardened” to such practices.
However, this may not be the case for most plants. Instead, they will suffer internal cold damage that may affect growth in the long term. Why? Simply because it wasn’t given enough time to warm up gradually. Think of it as waking up in the morning and immediately being put to work with no warning, forcing you to exert a lot of energy. Not so fun, huh?
Note: This does not apply to tropical, subtropical, and young plants (seedlings/saplings).
- Ruptured cells walls can’t prevent water overflow into other cells.
A plant’s cells contain water, sugar, and other solutes. When they freeze, the water transforms into ice crystals that expand within the cell wall and rupture the walls. The cells cannot keep extra moisture out with these protective barriers down. This can cause numerous cells to bloat and erupt, further damaging the plant.
Tender (seedlings/saplings) and cold-sensitive plants (tropical & subtropical) are more susceptible to this problem. They don’t have the defense mechanism to survive even a light frost because they originate from warmer climates. They just don’t vibe with the cold.
Cold-hardy plants have several ways of handling the frost, such as secreting an antifreeze substance to lower the freezing point of the cells. This can come in the form of protein or sugars, which is why root crops like carrots and radishes have a sweeter taste after experiencing frost. The more you know, right?
So, can you hose frost off plants? As a general rule, it’s better not to hose down plants to get rid of the frost. If the plant doesn’t show immediate frost/freeze damage signs, spraying it with water quickens the process or sets more problems down the line.
Why Does Spraying Frost Off Plants Work for Some People?
The consensus on this supposedly “effective” practice has mixed reviews. Some swear by it; others regret it terribly. I am more inclined to believe the latter because while the plants may look fine, they may not exhibit symptoms for a while after the damage has occurred due to the cold.
It is more likely that spraying frost off plants doesn’t work because they could suffer from chilling injury symptoms. This is a form of cold damage acquired after the temperature drops but not below freezing, think 40-50°F. It’s easier to spot this in tropical and subtropical plants because they exhibit purple or red wilting leaves. But for cold-hardy plants, there are often no immediate symptoms. But the internal cells of your plants took a small beating, and this may show over time in stunted growth, sudden plant death at worst, and in fruits, pitting, and discoloration.
Interestingly, commercial grows in edible farming productions use a constant misting method. The big difference is that they do it before the predicted frost, not after. They use micro-sprinklers to constantly mist water all over the plants to prevent ice crystals from forming. There is no dry moment for the crystallization to occur, keeping the temperature from dropping and impairing the plant’s cells.
HOWEVER, this works best for plants with thick fleshy leaves and fruits with tough skin. But for others? Only sometimes. They also use another method with high airflow fans to keep the surrounding air circulating and warm.
But either way, if you ask me, “should I wash frost off the plant?” The short answer is no because plants are likely to incur internal damages from the fast temperature change and that could affect their growth in the long term. A better alternative is to cover the plants before the predicted frost as a precaution or bring them in before the cold temperatures if the plant isn’t hardy enough to make it.
What To Do if Frost Forms On My Plants?
Sometimes, the inevitable happens. It could be out of carelessness, not enough garden fabric to cover your plants, or the frost coming out of nowhere without warning. The best you can do is salvage what you can and do better next time.
Here’s what you can do with frost-laden plants:
- Water the soil thoroughly before sunrise. This will help warm your plant gradually before the sun gives it more heat and light. Not only that, your plant could use the glug of water after a cold night. Note: Be careful watering your plants that are in terracotta pots. These can crack from the water expanding when it freezes. If the temperature is expected to drop again, either bring them inside or wrap a thick layer of burlap to keep it warm.
- Do not remove any frost-damaged parts of the plant. It may look unsightly, but it helps to insulate the rest of the plant if the weather is still cold. Note: if the damage affects ¾ of the plant, the plant is unlikely to recover and is best removed to prevent any pathogens feeding on the water-soaked and rotting parts.
- Cover the plant with garden fabric or bring it indoors. One of the worse parts of having frost on your plants is making the same mistake twice. If you’re not sure about the weather (read: don’t trust your local weatherman/woman), this is the best precaution you can take.
Don’t attempt to do anything else apart from the above steps. The chances are you’ll likely be making things worse for your plants if you go above and beyond to save them. They really can’t take anything more than gradual temperature changes.
If your potted plants are too cold for their health, you can learn how to warm them up slowly in this article.
How to Protect Plants from Frost?
The best and easiest way to protect your plants from frost is to cover them up. Secure woven fabric sheets such as fleece or burlap (Amazon links) tightly around your plants to prevent any cold wind from blowing them away. This failsafe method is more reliable than the whole watering thing. When the sun rises or the temperature has warmed up, ensure to remove the covers. This will give your plants the much-needed light and air circulation after a cold night.
You can use towels, blankets, or bed sheets if you don’t have any garden fabric on hand. You can also use an upturned cardboard box or large terracotta pot you have lying around! But that is more of a last resort situation. As long as it is made of material that allows your plants to breathe through and not suffocate, it will do.
The only thing you should never use to protect your plants from frost is plastic. Some have had success using them by supporting the material with tall stakes so it doesn’t touch the plants. If the plastic comes into contact with the plants, the trapped moisture will freeze against the foliage in the frigid weather. That just defeats the purpose of having a cover in the first place. So if you really have nothing but plastic on hand, use it with caution but preferably never use it.
Final Words
Hopefully, this helps answer any thoughts you had about washing frost off your plants. When in doubt, cover those plant babies for an overnight snow slumber party. Happy planting!
References:
https://www.canr.msu.edu/news/using_sprinklers_to_protect_plants_from_spring_freezes
https://content.ces.ncsu.edu/prevention-and-management-of-frost-injury-in-wine-grapes
https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1002.pdf
https://aces.nmsu.edu/ces/yard/melon_patch/2005/mar05.html
https://cals.arizona.edu/mohave/master_gardeners/kingman/articles/frostorfreeze.pdf
https://extension.psu.edu/understanding-and-preventing-spring-frost-and-freeze-damage-to-grapes
https://extension.uga.edu/publications/detail.html?number=B1479
https://vegetables.ces.ncsu.edu/2020/05/frost-and-freeze-protection-for-vegetable-crops/
https://chatham.ces.ncsu.edu/2016/04/protecting-fruit-plants-during-frost-or-freeze/
https://aggie-horticulture.tamu.edu/wp-content/uploads/2013/06/FrostsandFreezes.pdf
https://www.canr.msu.edu/news/frost-and-freezing-temperatures-and-ways-to-protect-plants
https://hortnews.extension.iastate.edu/1996/10-11-1996/firstfrost.html
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