The First Killing Frost Of The Season

Oct 19, 2018

It won’t be too long until we experience the first killing frost and that will end the 2018 gardening season.

In the northern valleys of Utah sometimes this can come earlier than we wish. Sometimes we still have apples on trees waiting to mature so they can be harvested. When apples are still maturing on trees when a hard frost is forecast gardeners are left to make some hard choices.

Apples on the tree will take a light frost down to about 28 degrees Fahrenheit without any real damage.  If a light frost is forecast it’s probably best to gamble and leave the fruit on the trees and hope for some Indian summer to allow the fruit to continue maturing. However, allow the fruit to warm above freezing in the morning before beginning to harvest. If a hard frost is forecast, that is below 28 degrees Fahrenheit, it may be best to harvest the fruit and hope for the best.

If the fruit has begun to color and if the fruit is not too starchy tasting, they are probably far enough along to harvest. They will continue to convert starch to sugar even after harvest. These fruits can be stored for later eating or processed into applesauce, cider or pie filling.

Another option for young trees is to tarp or cover the trees in the early evening to protect the canopy from the coldest temperatures through the night. The tarp should be installed before the air temperature is below freezing and should be removed in the morning as the air temperature goes above freezing. You could hang a burning 60-watt incandescent light bulb inside the tarp canape to add a little bit of heat. But remember the objective is to just keep the canape above freezing not to keep it warm.

If fall frost regularly occurs before some of your apples are mature you may need to consider planting a tree that matures a little earlier. That’s the best long-term solution.

This is Teryl Roper, Extension Pomologist at Utah State University.