Karl Foord, UMN Extension Educator
As you know, this has been another unique spring for Minnesota. We started out several weeks ahead of normal and lost some ground with a cold spell. Unfortunately, in some areas the cold spell was more than a delay. In certain parts of the state the nighttime lows on May 9th reached 25.5 degrees F.
Strawberry flowers are most vulnerable to frost damage when fully open. At this growth stage 30 0F will damage the flowers. The fruit can tolerate a few more degrees and sees damage at and below 28 0F. A "popcorn" stage closed flower bud shows damage at 26.5 0F and a tight bud at 22 0F. A damaged strawberry flower will turn black in the middle whereas a healthy flower will be yellow in the middle (Photo 1). This frost damaged open flowers and some "popcorn" flowers. All is not usually lost with strawberries as they flower over a two to three week period (note the variation in stage from open flower to young fruit (Photo 2) and the healthy clusters of young fruit that survived the frost (Photo 3). Look for pick-your-own strawberries to be available the second or third week in June depending on your location. Experience strawberry flavors beyond those available in grocery stores where the plants have been bred for shipping at some cost to flavor.
It took a week to discern what damage these low temperatures had done to apple flowers. Unfortunately, fields with early flowering cultivars that experienced these temperatures were damaged (Photos 4 and 5).
There may be some apples available as only 10% of the flowers are needed to produce a full crop. Note the size advantage in fruit that can accrue from being the first flower in the cluster to open - the king flower (Photo 6).
If your apple flowers were not damaged by frost and you experienced good seed set, it will soon be time to thin. The tree will naturally drop a number of these apples in the so called June drop, but it is likely that you will still benefit from your own thinning. Thinning to one fruit per cluster or spur is recommended. Proper thinning promotes big apples and helps to avoid alternate bearing where you have a surplus of apples in one year and a surfeit the following year. Photos 7 and 8 show and apple flower/fruit cluster before and after thinning. Keep an eye out for leaf rollers (Photo 9) and plum curculio.
Fruits are forming on the first raspberry flowers (Photo 10). We may see the end of strawberry picking overlap with the beginning of raspberry picking.
Sincere thanks to Apple Jack Orchards for permission to photograph their plants. Also thanks to Mike Dekarski and Tom Marxen for their insights into strawberry, apple, and raspberry culture. Photo credits: Karl Foord.