Frost-Proof Your Fruit Trees: How to protect fruit trees from frost with water, bed sheets and plastic tarps

If you are growing fruit trees, spring is a time of hope. As the weather warms and the days get longer, your fruit tree's buds will break open. Blossoms and leaves will emerge, and if pollination is successful, baby fruit will form.

But what if this happens too early in the season? And what if that spring weather is followed by a deep frost? Well, fruit tree blossoms can die and tender young leaves may turn to mush. A deep frost at the wrong time of year can even lead to the death of the tree.

This is something that Dr Kevin Folta has seen first-hand. He is a professor in the Horticultural Sciences department of the University of Florida, and his wife Natalia Derevianko owns and operates Eggsotics Farm in Archer, Florida. On her farm, Natalia produces eggs and vegetables for local farmers' markets, and she grows guavas, mulberries, persimmons, peaches, plums, pears, apples, jujubes and other fruits.

In late March 2022, Kevin was on "frost duty" when the local weather station issued a frost warning. Kevin was afraid that the temperature might dip to 27°F (-2.8°C) or lower - a temperature that can be fatal for many actively growing fruit crops. At that point, peaches had already formed on the trees, and the mulberry trees had leafed out.

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"I was so nervous about this. I went and sat in the car all night with my cell phone monitoring all our temperature monitors. We saw it go to like 39, 38, 37 degrees Fahrenheit (3.9°C, 3.3°C, 2.8°C). It got down to 36°F (2.2°C), at about six in the morning, and I decided I'd just pack it up and go home. So, I went home and went to sleep," he says in an interview on The Urban Forestry Radio Show and Podcast.

With the temperature well above the 27°F (-2.8°C) that can be fatal for many fruit tree blossoms, Kevin thought that the danger had passed. But while he was sleeping, the temperature dipped to 27°F for two hours, and that was long enough to wipe out their stone fruit crop that year. The mulberry trees also experienced damage.

"We lost quite a bit in a two-hour window," Kevin explains, "We probably lost several thousand dollars' worth of fruit."

Whether you have one fruit tree in your yard or hundreds of them in your orchard, it's important to be prepared for a possible frost in advance. With a few simple tools, including bedsheets, tarps, and a sprinkler, you can protect your fruit tree - and your harvest - from frost damage. So, if you're ready... let's dig in!

Why do you need to protect fruit trees from frost?

Most fruit trees can survive cold temperatures. In fact, fruit trees that grow in temperate climates like apples, pears, apricots, peaches, and cherries need a certain number of hours of cold weather (known as chill hours) to survive, thrive, and to produce a healthy harvest.

But the secret here is that the trees can only protect themselves from the cold weather when they are dormant. At that time, the branches are bare. There are no blossoms, leaves, or fruits on the tree. And the buds on the branches are tightly closed and protected from frosty temperatures.

When the days get longer and the weather warms, those buds will open, and young leaves and blossoms will emerge. Those tender plant tissues are vulnerable to the cold. A late frost where the temperatures dive below about 27°F (-2.8°C) can result in frost damage including:

• Dead blossoms – and if the blossoms die the tree can't produce a harvest for you that year.
• Dead leaves – when leaves die the tree may have trouble producing photosynthetic energy to support its biological systems during the growing season.
• Dead stems and branches – if the frost happens when the sap is flowing, that liquid will freeze and expand, causing cells to burst and die.
• Stunted growth – Cambial cells in the branches and trunk are responsible for cell division and Secondary Tree Growth (the widening of the branches over the years). If these cells die during a frost, you will see branch dieback, stunted growth, and in extreme cases even tree death.

What does frost damage on fruit trees look like?

In the case of Kevin Folta's orchard, the damage after the 2022 frost was obvious. All the trees were covered with a layer of frost. The frost damaged fruit on the trees fell off... and the fruitlets that remained on the trees went brown and rotted within days.

Here are some ways you might recognize frost damage on fruit trees:

• If tree blossoms die during a frost, you may see that the pistil, or female part of the flower, has turned black or brown. Sometimes you'll need to slice the blossom in half to see the damage.
• If baby fruit does survive the frost, there may be other problems. Remaining frost-damaged fruitlets may grow more slowly, and at harvest time, they may not reach their full size.
• If the frost kills the leaves, they might turn yellow and become mushy. Or you’ll see brown ridges on older leaves indicating that some of the leaf tissue died in the frost.

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Is there a temperature beyond which most blossoms will not survive?

Some fruit trees are more resilient when it comes to a late frost than others. Apple and pear trees can be tough. But stone fruits can be more vulnerable. Examples include early blooming apricots, almonds, plums, and peaches.

The other factor to consider is how long the deep freeze lasts. In some crops, you can get away with temperatures of 30°F (-1.1°C) for a short time. But when the temperature dips to 25-17°F (-3.9 to -8.3°C), even short exposure can be lethal.

"It is a question of time and temperature," Kevin explains. "The two things together really do synergistically affect how bad the damage is."

Ok, so it's clear that deep frosts during the active growing season can be a problem. How do we protect our fruit trees? There are three possible strategies. You can:

• Cover your fruit tree

• Protect your fruit tree from frost with water

• Choose frost-resistant varieties for future planting.

Let's explore each option.

Strategy #1: Learn how to cover fruit trees to protect them from frost damage

In 2021, the apricot trees in my community orchard in Toronto, Canada were in full bloom when a deep frost was forecast. And so, we volunteers decided to work together to cover the trees with tarps. Our hope was that the plastic would keep the blossoms slightly warmer during the frost.

We used our harvesting tools to lift the huge tarp up and over each tree and we stopped the tarps from blowing away by cinching them with a rope around the tree trunks. The result was charming. The trees looked like lollypops covered in a patchwork of colored tarps.

After the risk of frost had passed, we removed the tarps, and the blossoms were perfect. The trees produced a heavy harvest that year. But there is a right way and a wrong way to cover fruit trees to protect them from frost, according to Kevin Folta. And the most effective way to do this is through two-layer coverage.

• First layer: Fruit tree protection with fabric - First cover your fruit trees with a layer of fabric, using old sheets or blankets to create a tent around the tree. Use tent pegs and twine to secure the covering in place. Don't tie the cover to the trunk like we did. Instead, create an umbrella shape so that the tree can benefit from heat radiating from the earth.
• Second layer: Fruit tree protection with plastic - Next cover the fabric with a layer of plastic. You can use tarps. Or if you are preparing in advance, you may be able to find an old plastic liner from a backyard hockey rink in your neighbourhood.

Why does this two-layer, open-bottomed coverage work? Well, during the day, the sun heats up the earth. At night, when the weather is cooler, the soil releases some of that heat. And if you have your frost protective tree cover in place, that heat will become trapped under the canopy, keeping your tree warm enough to prevent frost damage on blossoms and fruit.

Once you have your fruit tree covered with an umbrella shaped canopy of fabric and plastic there are some optional extra steps:

Place buckets of water under the canopy to prevent frost damage to the trunk.

“I use five-gallon buckets on small trees, and I'll put them right up against the young developing tree. This helps protect the graft union from temperature deviations because just the contact with a larger mass of water will help that tree avoid freezing,” Kevin explains.

The other nice thing about water is that it releases heat. The water, which is usually warmer than the ambient temperature, will release radiant heat. That heat will be captured under your two-layer, protective tree cover, keeping your trees cozy even during a deep frost.

“Our water coming out of the well is 72 degrees Fahrenheit and you do see some of that heat escaping as visible condensation in the field,” Kevin says.

Use Christmas lights to keep plants from freezing.

Some people think that hanging Christmas lights on the tree will also help keep trees warm. But that won’t always work, according to Kevin. That’s because modern LED Christmas lights don’t produce much heat at all.

“If you have a grandparent who has those big, old, chunky incandescent bulbs, they do give off some heat and can be strung around a tree canopy to add a little bit of electrical heat - that is assuming that you have electricity that far out into a garden or grove,” he says.

But the downside is that Christmas lights is that the extra hours of light may confuse the plant!

“Light does mean something to a plant, Kevin explains, “and when you give it a light signal in the middle of the night, it can cause different things to happen, either poor performance in subsequent days or it even could change the way a plant flowers.

Roll a gas grill under the protective tree cover?

Jeff Neilsen is a home grower in Illinois, and if a deep frost is forecast he is prepared! He covers his trees with tarps. But in some situations, he will also roll his gas grill under the plastic canopy and turn it on low to keep the trees extra toasty.

Kevin will do that too from time to time.

“Sometimes we will shove our grill into our high tunnel on a really cold night and it works just fine,” he says. But that can cause other problems.

If you turn a gas grill on in a high tunnel, it could result in carbon monoxide poisoning! And fruit trees don’t adapt well to quick fluctuations in temperature. If the temperature quickly goes from very cold to very warm, that can cause tree stress.

So, if you’re looking for another way to protect your fruit tree and its blossoms from frost, Christmas lights or a hot grill may not be the answer. Instead, you may choose to protect your fruit tree from frost with water. And we’ll talk about that next.  

Strategy #2: Learn how to protect your fruit tree from frost with water

Emily Harding is a home grower in zone 8A in South Carolina. She grows peaches, plums, mulberries, Asian pears, and other trees in her garden. In recent years, there have been early warm spells that cause her trees to emerge from dormancy and blossom. But then often these warm spells are followed by deep frosts.

So Emily is prepared. With a deep frost is in the forecast, Emily will set up a sprinkler on a ladder near one of the affected fruit trees. Then, she will turn on the sprinkler before the temperature reaches freezing. If she waits too long, water can freeze inside the hose or tap, preventing water flow.

Then Emily will leave the sprinkler on overnight, and the blossoms will become covered with a protective layer of ice.  The hope is that the ice will insulate the blossoms, keeping them at 32 degrees Fahrenheit (0°C). So, when the temperatures dive even lower, the blossoms will be protected.

Kevin says Emily is on the right track.

“When the water comes out of the well or tap, it will have some heat in it. Then, when the slightly warmer water lands on the bud or on the tree, it'll leave that heat behind and impart that heat onto the object that you're freezing,”

But water does something else that's interesting, Kevin explains. When water is in it’s liquid form, the molecules move and jostle around. When they freeze, the molecules align together and make a crystal. They suddenly stand still, and the energy that they had been using to move around has to go somewhere – so it's given off in heat.

The result is that by running a sprinkler continually during a deep freeze event, you are encasing that bud, leaf, or blossom in a thin film of water, followed by a thicker layer of ice. As more water is sprinkled on, that fresh ice, as it freezes, produces more heat - which will add to the protective film of liquid water.

Once the frost is over and the temperatures go above freezing, the ice on the tree melts and the tree itself (and blossoms and fruits) should be unscathed.

“You do have to think about it and watch it carefully,” says Kevin. After all, too much ice can break branches on young trees. Still, protecting fruit trees from frost with water in this way can be an excellent strategy that can help save your crop.

Plant your fruit trees near a water source.

The ability of water to produce heat also explains why many growers like to plant their fruit trees near bodies of water like lakes, pools and even hot tubs!

“We have an old above-ground pool that was partially filled with water we never swim in. You can grow papayas next to it because they never freeze. That body of water - as small as it is - can keep the air around it warmer,” he says.

So, you can protect fruit trees from frost with water alone. Or you can use this technique together with the protective cover for extra protection.

Finally, you may want to choose cold resistant trees for future plantings. That’s what we will talk about next.

Strategy #3: Choose frost-resistant varieties for future plantings.

Leslie Mapes-Wade grows fruit trees in the North Georgia Mountains. This year, her plums blossomed more than three weeks early and that was followed by sustained temperatures between 23-28 degrees Fahrenheit (-5—2°C).

It was devastating. Leslie lost all her plums, peaches, and most of the pears.

Her strategy going ahead is to consider planting fruit trees that will be more frost resistant and easier to cover and protect in the years to come.

“We're moving to dwarfing, rootstocks and late blooming cultivars, so that we can try more aggressive frost prevention methods. We're trialing a bunch of cultivars to see what works in the coming years. Then we'll narrow it down to the ones that perform best.

And some researchers are working to develop new cultivars and winter hardy varieties that will be more resilient. But that can be a little tricky, according to Kevin.

“To develop the next great peach tree takes 10, 15 years, and so how do you shoot for a moving target? So, you try to come up with varieties that are more resilient to any kind of stress, whether it's stress caused by insect or pest pathogens, or whether it's weather stress.”

You can learn how to choose a resilient, easier-grow fruit tree for your unique location in OrchardPeople.com’s online course Researching Fruit Trees for Organic Growing Success.

Protecting fruit trees with helicopters or turbines?

So, what do the professionals do? How do commercial orchards protect their huge orchards? Well, some use a tactic that is out of reach for home or small-scale growers.

To prevent cold air from settling around their fruit trees, commercial growers may resort to setting up massive wind turbines or hiring helicopters to fly around and disturb the air above the orchard. By doing this, the warmth coming from the earth is kept close to the ground and cold air from above won’t sink down into the orchard.

But, if you don’t have a helicopter or huge wind turbine handy, that might not work for you!

Conclusion: What is the best frost protection for fruit trees?

In the end, the best frost protection for your fruit trees is the one that you can quickly and easily put into action. As a small-scale grower, being prepared is key. Make sure you have all the necessary tools and materials on hand, such as sheets, tarps, and a hose with a sprinkler. Don't forget to think ahead and plan how you will secure your covers to prevent them from blowing away.

Remember, protecting your fruit trees from frost is simple when you have a solid plan in place. To learn more about frost protection and other fruit tree care tips, check out the podcast linked below. And for a comprehensive guide to successful fruit tree growing, consider signing up for one of OrchardPeople.com's five-star rated online courses.

With a little preparation and knowledge, you can enjoy a fruitful harvest year after year. Happy growing!

Susan Poizner

Director, OrchardPeople.com Fruit Tree Care Education Online

Susan Poizner is an urban orchardist in Toronto, Canada and the author of Grow Fruit Trees Fast and Growing Urban Orchards. Susan trains new growers worldwide through her award-winning fruit tree care training program at Orchardpeople.com. Susan is also the host of The Urban Forestry Radio Show and Podcast and an ISA Certified Arborist.