Do you need to worry about early spring freezes?
Cold, windy, snowy weather shouldn’t concern fruit growers as much as calm, clear nights.
April 4, 2016 - Author: Mark Longstroth, Michigan State University
In early spring as fruit trees begin to grow, many people are worried that freezing temperatures will kill the buds of their fruit trees. These buds can handle very low temperatures in the winter. Just because they have begun to grow does not mean they will be killed by freezing temperatures. The swollen buds can often easily withstand cold temperatures in the teens. As the plants move past the swollen bud stage, they become susceptible to cold temperatures down in the low 20s.
There are a lot of factors to consider and all freezes are all unique. The bud development stage will determine if the temperatures are low enough to cause harm. The weather conditions before and during the freeze and especially the wind and dew point will determine how cold the lowest temperatures will be. Finally, the topography of the site influences the risk of injury as cold air will settle into the low areas leaving warmer air at higher sites.
Another factor is not all the buds die at once. The most advanced buds will be killed at a warmer temperature than slower developing buds. Some fruit varieties, such as apricots, develop very quickly and are more susceptible to freezes than slower developing fruit such as cherries, peaches, apples, blueberries and grapes.
In southwest Michigan, our relatively mild winter and warmth in March allowed many fruit trees to get off to an early start. Cooler weather has slowed development, but we have swollen buds and green tissue exposed. On our most advanced fruits, tiny flower buds are exposed. I expect some injury from temperatures in the low 20s and severe damage from temperatures in the teens. See the Michigan State University Extension article, “Freeze damage depends on tree fruit stage of development,” for more information. You can also view a table on the critical temperatures for tree fruit crops and another table with pictures, “Picture Table of Fruit Freeze Damage Thresholds. These can be used to estimate the risk of freezes to fruit buds.
There has been little movement in grapes, so they can still handle fairly cold temperatures. Strawberry flower buds are still in the ground and should not suffer any damage until we get close to 10 degrees Fahrenheit. Blueberry buds are at swollen bud to bud burst and would be damaged by temperatures below 18 F. Damaging lows into the teens are forecast for Tuesday, April 5, and Saturday, April 9, morning.
A lot depends on the conditions of the freeze. If it is cloudy or windy, there is little to be done. During a radiation freeze, there are several techniques growers can use to reduce or prevent freeze injury. Orchard wind machines are effective if we have a strong inversion and work under really cold conditions. Sprinkler irrigation systems are not designed to protect below the mid-20s and should not be used for freeze events into the low twenties. A lot depends on the dew point during a freeze as this is often close to the actual low. See “What is the difference between a frost and a freeze” for more information.
For more information on predicting freezes and their affects, see the following articles:
- Monitoring for the risk of frost and freezing temperatures
- Spring freezes and fruit bud damage
- What are radiation freezes?
- Analyzing and improving your farm’s air drainage
- Air moving fans for improved air drainage
- Moist, weed-free soil retains more heat
- Using sprinklers to protect plants from spring freezes
- Protect blueberries from spring freezes by using sprinklers
- Freeze damage depends on tree fruit stage of development
- 2013 bloom dates for southwest Michigan tree fruit crops
- Using Enviro-weather’s regional overnight temperature report during cold events
- Probability of a hard frost or freeze in the spring for some southwest Michigan fruit sites