Temperate fruits can tolerate very cold winter temperatures, yet, as we move into the warmer weather in spring, trees and small fruits lose their winter hardiness. As buds swell and development begins, the ability to withstand cold temperature changes with the growth stage. Late frosts do the most damage to fruit trees and plants because the buds are coming out of dormancy. Here in the Pacific Northwest, we do not experience the extreme temperature dips that are seen in other fruit-growing regions such as the east side of the mountains or the Midwest.

That said, the temperate nature of our growing zone often means trees will bud out early in response to a warm spell, only to be struck with a quick freeze that can ruin the coming year’s fruit. 

Frosted blossoms can result in little or no fruit, so it pays to take action to protect your lovingly grown fruit trees and bushes from a late-winter cold snap. Early swollen buds can often withstand temperatures in the teens (degrees Fahrenheit) without any damage. As buds develop and begin to open, temperatures in the low 20s can cause harm to fruit buds and perhaps developing leaves. In light of our recent temperature dips, you may want to assess your trees for crop damage/loss. 

The range of damage coincides with the growth stages and fruit species and even the cultivar.

Early in development, there is often a wide range between the temperatures that cause little damage and those that cause severe damage. Early in development, at first green and green tip stages, temperatures need to drop into the teens or lower to cause significant bud damage. As bloom nears, temperatures in the upper 20s can cause considerable harm to an early blooming species or variety and leave other fruit crops unaffected or with only slight damage. Near bloom, the range between slight and severe damage is very small. The stage of bud development determines how susceptible any given fruit crop is when freezes occur.

Here in the PNW, we are already well into the bloom stage of most stone fruits (cherry, plum, peach, etc.) You may see a significant decrease in this year’s yield if this snowfall coincided with the tender full bloom stage of your tree. If flowers have already been pollinated and the green fruitlets have begun to form, the damage may be minimal. There are many variables that come into play in regards to cold hardiness at this time of year, and you may likely see some effect to your crop this year. 

Check your plants when temperatures start to drop below 32F, and if they are showing no opening of flower buds, the flowers will survive and produce. If you do see signs of bud-break, this is the time to take action. 

Future Planning: Covering Blossoms to Protect Against Frost

When it comes to smaller fruits and dwarf trees, you may be able to cover the entire plant. For bushing fruit such as currants or gooseberry, consider using tunnel cloches or individual cloches. The best materials to use for a tree wrap are burlap or cotton. They prevent the cold air from coming into contact with the leaves and allow the moisture on the leaves to escape. An old comforter is effective, but bedsheets do not provide enough insulation to keep the plant from freezing. Plastic is not advised, but if you do use it, don’t let it touch the leaves themselves, creating a tent-like cover with stakes or rope. Stakes can puncture the material, so place something over the end – old tennis balls work well. Make sure it extends to ground level to trap warmer air next to the tree. Don’t forget to remove covers during the day to let insects in to pollinate the flowers!

Clearly, large trees cannot be covered up entirely, however, flowers higher up on the tree may remain warm enough and go on to produce fruits even if the blooms on the lower branches get zapped. Cover those branches that are accessible, ensuring at least the lower fruit is protected. 

Non-adapted fruit trees:

Several types of fruit trees are acclimatized to local weather conditions and can survive freezing temperatures. A properly cared for apple tree thrives in a cold climate, and plum trees are one of the best fruit trees to grow in a colder region. Pear trees also do well in the cold as long as they are healthy. 

Citrus and peach trees don’t like the cold and need protection from freezing temperatures. Keeping the ground around the trunk clear of mulch and ground cover allows the soil to absorb heat, which helps keep the plant warm. If you have a young tree, it is more likely to suffer damage to its tender wood, and should be protected accordingly.