University of California
UC Master Gardener Program of Sonoma County
Of the more than 2,000 varieties of apples found in the United States, not all are suited to California. Many, however, thrive in Sonoma County where there is enough winter chill to initiate flowering and fruiting, allowing gardeners to enjoy a wide range of colors and flavors to suit the palate. One of the most difficult aspects of growing apples is deciding which variety to plant. Fortunately, there are many local growers who will let you sample ripe varieties at their ranches or at farmers’ markets, then offer advice on selection, and information on growth habits and pruning.
Choosing an Apple Tree
- Apples, like many fruit trees, are best purchased bare-root from local nurseries January-March. Nursery personnel can advise about self- or cross-pollination requirements for each variety.
- Trees sold in local nurseries are all suited to this county, ensuring that our winter temperatures will be low enough to meet the needed chill factor to initiate flowering and subsequent fruiting. (A chill factor is the total number of hours between 32-45 degrees that a plant requires to set fruit. In Sonoma County the chill factor ranges from about 400-1100 hours.)
- Most fruit trees are grafted—a shoot, or scion of the desired variety, is attached above roots (the rootstock) of another variety. The rootstock controls the ultimate size of the tree. By mixing and matching various scions and rootstocks, growers can produce dwarf, semi-dwarf, and standard varieties of many different fruit trees, including apples.
- The graft leaves a visible bud union where the scion and rootstock meet. Look for a small jog on the lower stem, often where the trunk joins the roots, sometimes higher on the stem. It is important to note the placement of the bud union when you plant the tree.
- When selecting a variety, take into consideration the effect the rootstock will have on tree size at maturity. Rootstocks enable standard trees to grow 20-30 ft. high and wide; semi-dwarf to 12-15 ft., and dwarf varieties 7-10 ft.
- If there is not a rootstock available that will reduce the tree size of the variety you select, the tree can be kept low and compact with judicious summer pruning.
- Some nurseries promote a multi-grafted tree with 3-5 different varieties on one trunk. While this offers varied fruit and ripening times, a drawback is that one graft will become dominant and out-grow others on the tree. Such grafts should be labeled so that one is not inadvertently removed during pruning, either in summer or during dormancy.
- Young trees require frequent watering, but suffer in soggy soil or if the lower trunk stays wet.
- Each year, focus irrigation farther from the trunk so that supplemental water reaches roots as they gradually spread under the entire canopy.
- Mature trees require little supplemental irrigation if winter rains are substantial.
- Fruit thinning is critical to encourage vigor and limit stress on the tree.
- For the first 2 years after planting, remove all fruit from the tree as it forms in May. Beginning the third year, thin fruit to one apple per spur approximately every six inches along the branch. Thinning reduces the total numbers of apples but promotes the size of each one. It also prevents fruits from touching and limits spread of pests and diseases.
- Trees must be pruned every year, preferably in summer from mid-spring until early autumn to maintain convenient size and structure. Removing foliage may seem counterproductive but it reduces potential for vigorous growth, keeps trees at a manageable size, and promotes more blossoms the following spring.
- Some winter pruning may be needed to remove crowded or unwanted branches that were not visible when a tree was in full leaf. This generally means cutting out crossing branches, competing leaders, upward growing inside branches, and downward growing branches.
- When pruning, remove any branches that grow on the stem below the graft. Also remove any suckers that grow from the rootstock around the base of the tree. They can often be pulled off when small, or cut with a pruner. If desired, you can treat them with Sucker Stopper, which prevents them from growing back.
- Once any winter pruning has been completed, apply a dormant spray to the entire tree and over the ground immediately under the canopy to reduce the population of damaging insects.