I’ve received more than one inquiry about what one can do now to help alleviate potential frost damage hat may occur in the next week or two. The specific question has come up about the application of kelp extract pre-bloom to provide some level of frost protection. I must confess that I am quite skeptical such claims. I did my Master’s work studying kelp applications in an organic orchard and two of the three study years saw frost, and we saw no effect of the kelp treatments. While there are a number of non-replicated reports on the subject, a quick review of the peer-reviewed literature (there’s not much out there) indicates the same—no effect observed in most cases. There was one trial on pears completed in Macedonia that saw a slight increase in fruit set on trees that received a kelp extract treatment after frost, but a larger beneficial effect was seen on trees treated with gibberellins as you would have in Promalin.

One practice however for which there is ample evidence of providing trees with a general increase in vigor and ability to set fruit (notwithstanding a frost) is preharvest foliar fertilization. Now (half-inch green through pink bud stage) is a good time to think about applying a foliar nutrient tonic to help developing buds as bloom approaches. A combination of nitrogen, boron, and zinc is recommended and will help improve fruit set.

The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

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