Those spring frosts

The bane of any tender fruit producer’s existence is a spring frost, occurring at bud emergence, and which, depending on severity, can play havoc with the rest of the year. I have noticed that at Lostwithiel Farm the critical period is the first week of May, and that if we can get through it with nothing less than 2^oC our course should set fair. What is the likelihood of this happening?

Environment Canada has just made it easy to search historic weather data for just such trends. I have deliberately chosen a dataset for a location slightly colder than ours (100km to the NE) as being more representative than data collected near Lake Ontario. I have graphed both date and temperature of the latest event in May of equal to or less than 2^oC over the nine-year period for which data is available at this station:

What we immediately see is a high probability of a damaging event occurring at least mid-month or later, and that we should not be surprised by any late spring frost. The 2002 event, a negative reading on the May 25^th, would have tested anyone’s resolve.

However, another factor to consider here is tree size. I collected nuts widely throughout our region in 2002, in fact, it seemed to be a bumper crop, for I have not seen the like since. Frosts generally occur as a result of a temperature inversion, and my hypothesis is that a tall tree has most of its canopy above the freezing zone. What I hope eventually to see, as our trees grow taller, is a declining effect of spring frosts on our own nut production. It is possible that many of the trees out in the landscape have been naturally selected for late flowering, though I don’t place much confidence in this. As far as I know, our first-planted trees are derived from nuts collected in our own seed zone. I actually believe lateness in bud emergence (and thus flowering) runs counter to the natural trend, and that earliness is of evolutionary advantage, but this is nothing we shall prove at the farm. What we will test is the heritability of date of bud break in the 25 lines selected this year, and see whether there is any consistent lateness between maternal and F1 lines.