As Mother Nature begins to taunt us with brief periods of warm weather in late winter, when should we start to worry about the various fruits we’re striving to grow? A late winter or early spring warm spell followed by a cold snap has the potential to wreak havoc on horticultural plants.
Until the spring green-up, buds are tightly closed and relatively safe to endure winter temperatures in their dormant state. As flower buds (which will eventually become the fruit) begin to open up in the spring, they become more sensitive to colder weather. If it is too cold for too long in this more vulnerable condition, the buds will freeze and die, resulting in no fruit.
Several factors affect how vulnerable plants are to late freezes. One is the general region where you live (the macroclimate) and its tendencies, such as areas that receive lake-effect snow.
There may be protected areas that form somewhat of a microclimate. Terrain and elevation factor in. If you’ve ever ridden a motorcycle at night, you have become keenly aware that air is colder in the dips in the road. In growing areas, plants in lower terrain may have more frost damage than those in a slightly higher elevation.
With vegetables, there are what we consider cool-season and warm-season vegetables. Cool-season vegetables like radish, kohlrabi, and broccoli can be planted earlier and withstand a few frost events. Warm-season vegetables like tomatoes, peppers, and squash are generally planted after the danger of frost has passed in the spring.
Small fruits and tree fruits have occasionally experienced cold damage from extreme cold in the wintertime.
Bruce Bordelon, retired Purdue small fruit specialist said, “Ten below zero is a commonly accepted threshold for seeing damage to cold-sensitive crops.” Damage will also depend on the cultivar, the duration of the cold, and mulching. He said that injury in grapes depends largely on the cultivar. Extreme cold temperatures can also affect blackberries, raspberries, and strawberries.
Strawberries are a commonly grown small perennial fruit we worry about with late spring freezes. In these events, growers may need to provide freeze injury protection, such as overhead irrigation, floating row covers, or straw mulch.
For tree fruits, pome fruits (apple, pear) are generally more cold-tolerant than stone fruits (peach, cherry, nectarine, apricot). Peach is a tree fruit that many enjoy, and local growers of peach are frequently let down by a spring freeze that has killed most or all of the flower buds. Many of the same factors previously discussed also apply to tree fruits. As mentioned, if flower buds have begun to grow, or flowers are out, the tree fruit crop is much more at risk.
For more information, access the Purdue Extension publication, “Effects of Cold Weather on Horticultural Plants in Indiana,” available at https://edustore.purdue.edu/.