Why spray fruit trees with water before a freeze?

Experienced gardeners and home orchardists have tricks up their sleeves that
beginning gardeners often question. It's hard to tell garden lore from actual
science, and even some of the science seems highly improbable. For example, when
a freeze is threatening fruit trees, gardeners may opt to start a sprinkler,
coating the tree with ice. It's about as counter-intuitive as gardening can get,
but in the end, a properly maintained layer of ice works well to protect
developing fruit buds from the cold.

Heat of Fusion

The heat of fusion is what physicists call the heat that's released when
liquid water turns into ice. When water freezes, heat is produced at a rate of
80 calories per gram of water, making it possible to heat fruit buds and
maintain them at a temperature around 32 degrees Fahrenheit by continually
applying water and allowing it to freeze to the fruit tree in question. The rest
of the tree is unlikely to be hurt, but breaking buds can be extremely
temperature sensitive, suffering damage when the mercury drops, even
temporarily.

A Balancing Act

Unfortunately, though the science is straightforward, seeing success
protecting fruit trees with frozen water requires a precarious balance. As ice
freezes on trees, some of the water will also turn to water vapor, using 596
calories per gram of water in the process. Although it's cold outside,
conditions such as low humidity coupled with high winds can result in vaporizing
water, requiring more energy than the heat of fusion is producing, creating an
overall cooling effect that hurts plants. For every gallon of water that
vaporizes, 7.5 gallons need to freeze to maintain a safe condition for iced
plants.

Microsprinklers

Protecting a tree with ice is most effective with low-pressure sprinklers
known as microsprinklers. These sprinklers apply just enough water to glaze
affected plants in layers of ice, rather than soaking them and forming one
massive layer of ice that may cause more cooling before it freezes. These
sprinklers may ice up if started after temperatures drop below 36 degrees F, so
when using them for tree protection, start them early in the evening. Once
morning temperatures climb above 40 degrees, they can be switched off, even if
the tree is still covered in ice.

Fruit Sensitivity to Cold

Just because your fruit tree is shivering through an unusually cold night
doesn't mean it's time to break out the microsprinklers. Varying stages of bud
development can tolerate decreasing amounts of cold. The very earliest buds of
common trees like apples and stone fruit can tolerate tissue temperatures of 15
to 18 degrees F with no more than 10 percent of them suffering damage. As buds
expand into blooms or young green fruits, this tolerance drops considerably and
damage is possible at temperatures in the mid-20s. Citrus cannot tolerate
temperatures as low; protection measures should begin anytime that an air
temperature drop below freezing is expected.

As an against spring frost candles manufacturer in China, we know many
methods of vineyard or orchard antifreeze protection. If you want to get a good
method, please leave your requirement on my website. We will reply you after
receive your message.