by Marla Koss
By the time this newsletter reaches your inbox, Alameda will have accumulated over 600 chill hours* since November 1. This means all the following deciduous fruit trees should have their dormant (winter) pruning done by the next week or two (or ideally, already have had it), depending on variety (presented here roughly in order of sap rise and blossom time):
- Plums
- Pluots
- Peaches
- Nectarines
- Asian Pears
- European Pears
- Apples
- Figs
- Persimmons
- Pomegranates
Note that apricots, grapes and cherries are not pruned this time of year, but are pruned in July/August. Do not prune these in winter in California. According to the UC Agriculture and Natural Resources division, this helps guard against Eutypa infection during rainy weather.
*Chill hours are 60-minute units — day or night — when the outside temperature hovers between 45 and 33 degrees F. It’s measured by the deciduous fruit and nut growers’ calendar from November 1st to February 28th. According to longtime County Extension figures, mild-winter Alameda receives as much as 500 chill hours in a winter only half the time, and many fruit varieties need more than that (ergo, “low-chill” varieties predominate in our local nurseries).
Adequate winter chill allows a deciduous fruit tree to break dormancy only once it has received the chilling it needs. Some fruits, like Persimmons or Figs, need as few as 100-200 chill hours per winter; some apple, peaches and cherries need 800 to 1,200 and will eventually fail in a warmer-winter area like ours.
Photo by Marla Koss