Wednesday, May 8, 2013

Comparitive Phenology for this Season

Freeze damage on apple. Late flowering
or leafing fruit trees may avoid freeze
damage in most years.
Phenology is the study of periodic life cycle events in plants and animals including such things as date of emergence of plant leaves and flowers. It is influenced by seasonal variations in climate (chief among these temperature) as well as location factors such as elevation.  This year there has been much discussion among gardeners about how "late" the Front Range season is in terms of plant emergence. Is it really?

Phenology is applied to crops in terms of dates that flowers will bloom or crops reach maturity. This is often expressed as a minimum number of "growing degree days", a measure of how much warm weather you have at your site. It's obvious that in springtime this applies more to fruit trees flowering or leafing out than vegetables but it could apply later to vegetables in terms of length of growing season.

So what's the story this year? Are we having an unusually late flowering and leafing out of fruit trees (as well as shade trees and shrubs)?

Looking at Denver weather data and running the formulas, degree days accumulated by the first week of May show we are 1 day ahead of the 30 year normal. Compared to 2012, we are 32 days behind and compared to 2011 we are 20 days behind.

What this means is that we have gotten spoiled. We have been used to plants leafing and flowering 3 to 4 weeks ahead of average so that in an average year like 2013 we think the growing season is off to a late start. Enjoy a normal growing season for once.

Photo credit: Freeze damage on apple - Carl Wilson

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