It has been an interesting Spring here in Westford, weather-wise. April dipped below freezing on the 3rd, 8th, 9th, 15th and 16th. Then we got a warm spell, a week of days that reached 75 °F (23 °C) and even one day that reached 87.4 °F (30.8 °C) (April 23rd). Then it struck, on May 1st, an overnight low of 28.7 °F (-1.8 °C).
The vulnerability, when a late frost like this occurs, is in bud development. If the plant, by warm sunny days, has been tricked into bud development, and then a freeze occurs, the bud will be injured or killed. Strawberries are particularly prone to this problem.
Because of interactions of thermal inversions at the ground, humidity levels, etc., a simple temperature reading is not an accurate indicator of whether damage actually occurred. For example, if humidity is high, the temperature can dip to freezing, but in the act of freezing water vapor (creating frost) energy is released (latent heat of fusion, as the chemists call it). So you have a few degrees of tolerance if humidity is high, if you have a fog, etc. In fact, commercial strawberry growers will handle this problem by running sprinklers when a freeze threatens, to increase the amount of water around the plants available to freeze, as a buffer to protect the plants. Every degree helps.
But I wasn’t so lucky. The extent of damage was not clear until the strawberry plants started blooming this week. Here’s what I am seeing.
Above is an example of a normal, healthy strawberry blossom. You see the ring of stamens, the male organs of the flower, each with a filament stalk tipped with an anther containing the pollen. In the center is the receptacle with the many carpels, which are the female side of the equation.
But in the picture below, we see a blossom from my garden that shows injury. Although the plant is sound, and it did flower, the carpels are dead. This blossom will not yield a berry.
From the looks of it, 40-50% of buds are damaged in this way. So no strawberry wine this year. I’ll only have enough for fresh eating and ice cream.