|Frost apparent on tomato leaves.|
Temperatures dipped only into the low 30's F on Oct 3, 12 and 27 in Denver, well within the ability of frost covers to handle. The weather otherwise was warm enough to keep tomatoes growing late and certainly warm enough for mid-season planted greens and root vegetables to mature nicely.
This all came to an end on November 10 with a low of 13 degrees F followed by subzero F lows the next three nights. These temperatures are way beyond the ability of frost covers to handle and effectively ended the growing season for those using frost protection. True to life in Colorado's high altitude steppe climate, daily highs in the 50's and 60's were recorded the end of the month.
The unknown factor about this generally warm late growing season suddenly ended by subzero cold is the possible damage to fruit trees. The most obvious sign of this now is the retention of leaves on apple, cherry and other fruit (and ornamental) trees.
The cold obviously interfered with the normal leaf abscission process but less clear is how much damage might have occurred to buds and wood. This won't be fully known until spring when lack of bud break and dead wood will show us the extent of any freeze damage. Lack of gradually cooling weather to promote full development of dormancy can deal a crippling blow to fruit trees exposed to sudden subzero temperatures. Let's hope for the best.
Note for those interested in growing fruit trees, I will be teaching a new fruit tree growing class at Denver Botanic Gardens on March 14. See clickable link to DBG in the 2015 class offerings found in the right column.
Photo credit: Frost on tomato leaves, Leaf retention on cherry - both credit Carl Wilson