CORPUS CHRISTI - A warm January has Spring Fever in full gear. Some plants are already starting to bud out with new growth. One thing that is missing, however, are some spring blossoms on peach trees and other early spring blooming trees.
Temperate fruit trees and shrubs are known for their barren, winter dormant form which is followed by a burst of blossoms before leaves. This year, don’t be surprised if you find few flowers.
Research has shown that one of the protection mechanisms in temperate spring-flowering plants and trees is the accumulation of “chill units.” A chill unit is the number of consecutive hours that plants remain in a range around 33-35 degrees. Once a certain number of chill units are obtained, then internal mechanisms allow flowering once temperatures rise at the beginning of Spring.
Unfortunately, the chill unit accumulation process is not a simple addition. Plants don’t accumulate chill units at temperatures below 32 degrees. Also, partial chill units accumulate at temperatures of 36-50 degrees with higher temperatures resulting in lower percentage of chill unit accumulation.
When temperatures are above 55 degrees, then plants not only fail to accumulate additional chill units, but they start losing some of the chill units accumulated. That’s why the sporadic cold weather we had earlier in the season has not satisfied the dormancy requirement of these trees.
What is typically found in these situations is nonuniform flowering over several months as a few buds start to open. That will likely result in less fruit production for those gardeners brave enough to attempt growing peach, nectarine, pear, and apple trees.
Scientists have been working on breeding plants for warmer climates. However, a gardener has to look at regional averages over many years to determine the best number of chill units for the area. Inland areas of the Coastal Bend typically look for fruit tree varieties in the 250-350 chill unit range. Coastal areas that don’t get quite as cold may be able to plant varieties with 200-300 chill units.
On a normal year, trees with those chill units should result in uniform spring blooming. However, the roller coaster temperatures earlier in the season have negated many of the previously accumulated chill units.
If all of this talk about chill units seems too confusing, then you might want to focus your fruit growing efforts on citrus and figs which are not dependent on cold weather.
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