Experienced gardeners and home orchardists have tricks up their sleeves that beginning gardeners often question. It is difficult to tell garden lore from real science, as well as a number of the science seems highly improbable. For example, when a freeze is threatening fruit trees, gardeners might opt to start a sprinkler, coating the tree using ice. It is nearly as counterintuitive as gardening can get, but in the long run, a properly maintained layer of ice works well to guard developing fruit buds from the cold.
Heat of Fusion
The heat of fusion is what physicists call the heat that is released when liquid water turns into ice. When water freezes, heat is created at a speed of 80 calories per gram of water, making it feasible to heat fruit buds and maintain them in a temperature approximately 32 degrees Fahrenheit by continuously applying water and letting it freeze to your fruit tree in question. The remaining part of the tree is unlikely to be hurt, but splitting buds can be extremely temperature sensitive, enduring damage once the mercury drops, even temporarily.
A Balancing Act
Unfortunately, although the science is straightforward, watching success protecting fruit trees using frozen water calls for a precarious balance. As ice freezes on trees, a few of the water will even turn into water vapor, using 596 calories per gram of water at the procedure. Even though it’s cold outdoors, conditions such as low humidity combined with high winds can result in vaporizing water, demanding more energy compared to the heat of fusion is producing, creating an overall cooling effect that hurts plants. For each gallon of water that vaporizes, 7.5 gallons need to freeze to maintain a secure condition for plants that are iced.
Maintaining a tree using ice is most effective with low-pressure sprinklers called microsprinklers. These sprinklers apply only enough water to glaze contaminated plants in layers of ice, rather than soaking them and forming one gigantic layer of ice that may cause more heat before it freezes. All these sprinklers may ice up if started after temperatures fall below 36 degrees F, so if using them for tree protection, start them early in the evening. After 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 as your fruit tree is shivering through an unusually cold night does not mean it is time to break out the microsprinklers. Varying stages of bud development can withstand decreasing amounts of cold. The first buds of trees that are common such as apples and stone fruit can withstand tissue temperatures of 15 to 18 degrees F without more than 10 percent of these suffering damage. As buds expand into blooms or youthful green fruits, this tolerance drops considerably and hurt can be possible at temperatures at the mid-20s. Citrus cannot tolerate temperatures as low; protection measures should begin everywhere that a air temperature fall below freezing is anticipated.