Orchard frost protection

One late freeze in the spring can ruin a good fruit tree crop. Once the trees start blooming, the critical temperature to start seeing significant loss is 28-degrees. Depending on the species, it may only take a few minutes for damage to occur.

Joe Hannan is a commercial horticultural field specialist at Iowa State University. He says your options for protecting the delicate blooms can depend on the type of freeze.  Advection freezes come from cold air blowing through in both the upper and lower atmospheres. The only way you can provide protection is by putting blankets or some other cover over the plants. A radiation freeze is what we tend to see more in the springtime. We have warm air up in the atmosphere and cold air at ground level.

"A lot of times we’ll have air movement throughout the night and then just as the sun is starting to come up, the air movement will just absolutely stop and then the cold air starts to settle in place around the plants," says Hannan. "That’s where heaters, blankets, sprinklers, air mixing machines, those are the methods that provide protection underneath for a radiation-type freeze."

Good soil moisture can help, too. Soil that’s moist harnesses more heat than dry soil and can warm the air near the surface.

"That warm soil will keep a little bit more energy and will give off a little bit more energy into that microenvironment around the tree. So, if we’re a couple days out coming into a frost, if the ground is dry, putting some water out there that water in the soil will store more energy."

Keep the area around the tree trunk either bare or mulched. Grass and weeds make it harder for warm air to rise up out of the soil.