This is copied from an e-newsletter distributed by the Kansas State agriculture college. It is a great resource for determining how much freeze damage can by done to Apricot and Peach trees and how to test. The severity of damage depends on temperature range, what stage the blooms were in, and how warm it was prior to freeze. In Kansas, peaches and apricots often don't produce due to cold damage. Many KS growers say they average a crop 1 out of 5 years. This publication also offers some tips on protecting the blooms and how to test for freeze damage.
It seems we have had the perfect storm this year for bloom loss. Last week the temperatures were in the mid 70's and this past weekend we have dipped down into the low 20's and temperatures continue to drop there at night.
Horticulture 2017 Newsletter
No. 11 March 14, 2017
FRUITS
Frost Tolerance of Apricots and Peaches
Growers of apricots and peaches often wonder at what temperature fruit buds are killed especially in years where we have an early spring. These two tree fruits bloom very early and are often caught by a late frost. The following will give you some guidelines but remember that the actual damage is going to be influenced by the weather before the temperature drops. An extended warm spell before the cold snap may result in more damage due to a loss in cold hardiness. The stages listed are for the fruit buds.
Apricot
Stage 10% Kill (°F) 90% Kill (°F)
First white 24 14
First Bloom 25 19
Full Bloom 27 22
n the Shuck 27 24
Green Fruit 28 25
Peach
Stage 10% Kill (°F) 90% Kill (°F)
Swollen bud 18 2
Half-inch green 23 5
Pink 25 18
Bloom 27 24
Petal fall 28 25
Fruit set 28 25
To check for low temperature injury to fruit buds or blossoms, use a sharp knife and cut them in half longitudinally (from top to bottom). If the tiny seed in the center is white to cream color no damage has been done. But if the seed in several buds or blossoms is dark brown or black, it has been killed.
It is possible to give some protection to blossoms from freezing by covering the tree with a bed spread, blanket or similar fabric. Old-fashioned Christmas lights distributed around the tree will help to give additional protection. The newer, smaller Christmas lights do not give off enough heat and are not recommended. Of course the practicality of this method of protection depends upon the size and number of trees.
Sprinkling the tree with water throughout the freezing period can also protect the blossoms. Sprinklers should be started before the temperature drops to freezing to be sure ice does not block the garden hose or water line. Continue until the temperature warms. With this protection method, there is the potential of creating an ice storm. If temperatures remain below freezing for several hours, ice will accumulate on the branches and limbs. The weight from the ice may cause branches and limbs to break causing severe, and possibly permanent, damage to the tree structure. Also, if water drainage from the soil is slow and the water displaces oxygen from the roots, damage to trees may result. (Ward Upham)