Whether spring or fall, a drop in temperature means there’s a danger of frost. And frost puts your vegetable garden at risk. You may have heard watering your garden before a frost is a good way to combat this threat.  Is this something you should do?

You should water your garden before a frost to help prevent damage from the cold. When a plant’s cells are filled with water they’re stronger and more resistant to cold weather. Too, moist soil stays warmer than dry soil. However, improper watering can create problems, and not all your plants may be protected.

Read on to learn more about watering your vegetable garden before a frost, and which plants are most vulnerable.

Watering Your Vegetable Garden before a Frost

When temperatures dip, gardeners worry about frost. With good reason. 

Frost can damage and even kill some plants. 

Why You Should Water Your Garden before a Frost

As temperatures drop below freezing, ice crystals can form on a plant. These crystals, coupled with the cold air, draw moisture from the plant’s cells. In other words, freeze-drying them. 

Watering before a frost helps the plant stock up on moisture. This, in turn, helps prevent the cold from drawing more moisture than the plant can handle. 

But, watering doesn’t only help the plant prepare for the cold. 

Moist ground stays warmer than dry ground.  In fact, moist ground can hold up to 4 times more heat than dry ground.

This wet soil absorbs heat throughout the day and radiates that heat at night. Then, as the soil releases the moisture, it warms up the air around the plant. And the more humid the air, the better it retains heat.

When Does a Frost Happen?

Whenever the temperature drops below 32 degrees Fahrenheit or 0 degrees Celsius, there is the potential for frost.

A light frost or freeze occurs when the temperature drops between 29 to 32 degrees Fahrenheit or -1.7 degrees to 0 degrees Celsius.  Even a light frost can destroy tender plants.

When the temperature drops between 25 – 28 degrees Fahrenheit or -3.9 degrees to -2.2 degrees Celsius, this can cause a moderate frost or freeze. This level of frost is more destructive and damaging to vegetation.

A severe frost or freeze occurs when temperatures drop to 24 degrees Fahrenheit or -4.4 degrees Celsius and colder.  This temperature causes heavy damage to most garden plants.

Different geographical zones have different frost dates. To learn more about the frost dates in your area take a look at this article by the Old Farmer’s Almanac.

Hardy, Frost Tolerant & Tender Vegetables

Different vegetables can tolerate different drops in temperature.  

Hardy vegetables – hardy vegetables are tolerant cold better and can, with some help, potentially withstand a hard frost.

Examples of hardy vegetables include;

• Broccoli
• Kale
• Cabbage
• Kohlrabi
• onions

Frost Tolerant – frost tolerant or semi-hardy vegetables, on the other hand, can withstand light frosts, even several in a row.

Frost tolerant vegetables include;

• Celery
• Beets
• Cauliflower
• Potatoes
• Leaf lettuce

Tender – tender vegetables, as the name suggests, are tender in nature. They’ll likely be damaged by even a light frost. Watering beforehand may not be enough to protect this category of vegetable. So, if you have tender vegetables in your garden, take extra care to protect them from any type of frost. 

Examples of tender vegetables include;

• Cucumber
• Beans
• Eggplant
• Tomatoes
• watermelon

When to Water Your Garden before a Frost

The best time to water your garden is the day before a predicted frost.  However, it’s okay to water a day or two earlier, if you know you won’t be able to water the day before. The main goal is to keep your soil moist.

Water in the morning, when the temperature is at least 40 degrees Fahrenheit (4.4 degrees Celsius) or above.

On the night of the frost, before temperatures dip too low, you can sprinkle more water around the base of the plant. This helps keep the ground moist overnight.

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Want to learn ways to prepare your vegetable garden for winter? Check out my post on the subject.  You’ll find it helpful.

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If you miss the chance to water before a frost, it’s important to water your garden the next day.  Especially if the ground froze, as your plants may not be able to access water from the frozen ground. Water later in the day after the plants have had a chance to warm up. 

With a light frost, you can sprinkle water on your plants before the sun rises. This can help remove the frost and help the plant better acclimate to the temperature change from the sun.  

The key here, though, is doing this before the sun touches your plants. Spraying them once the sun hits can raise the plant’s temperature too quickly, which can damage its cells.

Don’t water your plants if your garden is already wet from rain, or if you expect a good amount of rain before the temperature dips.

How Much Water to Give Your Plants before a Frost

How much water you give your plants before a frost is very important. Too much or too little water can damage your plants if a frost hits.

First, make sure you water your whole garden and not just your tender plants.

Give your garden a thorough watering, so the soil is evenly moist, but not soaking.

The goal is to ensure each plant’s root system has water.  This is because moisture around the root system helps insulate the roots. So, adequate watering is vital.

However, when it’s cold outside, plants don’t need as much water. So it’s also important you provide only as much water as your plants can absorb.

Not only can too much water damage your plants, and it can cause frost heave.

Frost heave happens when the soil is exposed to freezing temperatures and lots of moisture.  The combination of freezing and thawing creates pressure that can heave the soil and lift your plants from the ground.  This article from Gardening Know How gives a greater explanation of frost heave. 

Giving too much water is why it’s important to hold off on watering if there’s been significant rainfall.

Final Thoughts

• You should water your vegetable garden before a frost.
• Watering will help insulate the plant’s roots and make the cells stronger.
• There are different levels of frost, which can be damaging to different types of plants.
• Both when to water your garden and how much water to give your garden are important considerations.

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