Gardening : Deciduous Fruit Trees Just Need to Chill Out
You’ve been looking at your deciduous fruit trees. You’ve searched in vain for fruit bud and leaf buds.
“It’s mid-spring--what did I do wrong,” you wonder. You are not alone with this problem. Every year dozens, perhaps hundreds, of Bing cherry and Bartlett pear trees, among others, die a slow and painful death. At least their death is slow and painful to the owner. Sadly, their demise was assured when the first shovelful of dirt was tossed in the planting hole.
These trees, planted with tender care by unsuspecting gardeners, were grown in a cold climate. They will thrive the first season. Their leaves will turn color and shed in the fall, going into normal dormancy. Then they will remain leafless through the winter--and the spring--until their bare branches are destroyed by sunburn or insects. Or the homeowner just gets disgusted and pulls them out. The reason? Not enough cold weather in balmy Southern California to meet the chilling requirements of these cold-loving plants.
The examples given above, of cherry and pear trees, are the extreme because they need the most cold. They will not survive here. Much more common in home gardens are the deciduous fruit trees that bear fruit marginally. These trees start the spring grouchily, like a hibernating bear that has had its sleep interrupted. They leaf out slowly, with few if any fruit buds. They eventually develop healthy foliage but little fruit. Good crops are produced only after our coldest winters.
For example, 1987-88 was a very cold winter. Residents were ready to lynch San Diego Gas & Electric officials because of high fuel bills. But gardeners everywhere had bumper crops of apricots, plums, peaches, etc., the following summer.
Outrageous heating bills and good crops do not have to go together. Not if you understand chilling requirements of deciduous fruit trees.
This chilling requirement, also appropriately called rest period, is roughly analogous to our sleep requirements. However, the trees do all their “sleeping’ once a year. To get the “sleep” they need, the temperature must be below 45 degrees Fahrenheit. This cold must be continuous. A warm, sunny day to a peach tree is like a rock drummer playing outside the window of an insomniac. It breaks up the tree’s rest and it must start all over again. So a couple of frosty nights will not do the job.
This rest period varies a great deal. The Bing cherry, for instance, requires 1,200 hours below 45 degrees--almost two months. Fortunately, like men known to get by on only three hours sleep a night, there are trees that need a very short rest period.
Dr. Henry Chandler, a University of California plant scientist, made the first scientific study of chilling phenomena in 1937. Plant breeders have since searched out “warm winter” plants from around the world. These trees with very low cold needs have been crossed with better flavored high-chill varieties to produce superior fruits for our climate.
The University of California has a list of warm winter varieties that do well in our county. This information can be obtained by calling the Farm and Home adviser’s office, (619) 694-2845. Ask to talk to one of their master gardeners.
Evergreen Nursery, located at 7150 Black Mountain Road in San Diego, lists the chilling requirements of all their deciduous fruit trees on a handout sheet. I asked Barbara Wood, Certified California Nurserywoman and assistant manager of Evergreen, for some broad planting guidelines.
“In the immediate coastal areas and frost-free regions of the county, plant trees requiring 150 to 300 hours of chilling, Wood advises.
“If you live on the colder valley floor, 350 to 400 hours will be suitable. Julian and similar altitudes will handle varieties needing 500 to 700 hours below 45 degrees.”
If you have an addiction to those luscious Bing cherries as I do, you’ll have to buy them in the store. No one has come up with a good warm winter cherry. But there are plenty of apples, apricots, peaches, etc., adapted to our weather. Just be sure to plant the right varieties. If you don’t, the results can be chilling.
Deciduous Fruit Trees for Southland
Here is a list of deciduous fruit trees for Southern California’s mild climates based on recommendations by the Cooperative Extension in San Diego. For a more complete list, including varieties that are not recommended, send a stamped, self-addressed envelope to U.C. Cooperative Extension, Building 4, 5555 Overland Ave., San Diego, Calif. 92123 and ask for County Publication CP336. Their complete list shows many more varieties that will succeed away from the coast in more inland climates. “Needs pollinizer” means there must be another variety of the same fruit tree in the area.
Apples Peaches: Anna August Pride Beverly Hills Desert Gold Einshemer MidPride Golden Delicious Royal Gold Gravenstein (needs pollinizer) Shanghai Valmore Springtime Winter Banana Tropi-berta Winter Pearmain (needs pollinizer) Ventura Apricots: Persimmons: April Gold Fuyu Autumn Royal Hachiya Flora Gold Newcastle Plums: Nugget Santa Rosa Nectarines: Pomegranates Desert Dawn Wonderful Goldmine
