Plums can be grown in any state in the country, but they vary so widely in hardiness that no one variety can be grown everywhere. The search for a suitable variety is worth the effort: the small size, even of standard trees, simplifies pruning, spraying, and Harvesting
Varieties
Double-check two details as you select plum trees: are they suitable for your climate? will they need a second variety planted nearby for cross-pollination? Although many varieties of plums are available, Abundance, Burbank, Ember, Pipestone, Purple Heart, Stanley Prune, Mt. Royal, and Underwood were all developed in northern areas and can withstand tough winters. Most varieties can be found only in the standard size (up to 20 feet tall), but Abundance, Burbank, and Stanley Prune are also in dwarf form. If your winters aren't brutal, consider the tasty Damson, Superior, or Green Gage (also called Reine Claude).
Many catalogues will differentiate between European or Japanese plums. European varieties tend to be best for cold-weather areas. Japanese varieties, such as Shiro, are a reward for gardeners in areas seldom surprised by late frosts; they bloom earlier than European.
Only a few plum varieties are self-fertile. Stanley is one, but it also makes a good pollinator of other Varieties Others, such as Underwood, Redheart, Shiro, or Santa Rosa, benefit if two or more trees of the same variety are planted in the same area. Or they will act as pollinators for other Varieties
Planting
Most plum trees are best planted in early spring, as soon as the soil will allow. European varieties can also be set in the ground in late fall. Space standard-size trees 20 feet apart, with graft union above the soil line. A northern slope is ideal, especially for the early blooming Japanese Varieties Good drainage is essential.
Most standard and dwarf plums take at least three years from planting to reach the bearing stage. But standards will last up to 20 years, dwarfs up to 15.
Care and feeding
Mulch is an aid to plum trees all year. In early spring, it can keep roots cool so the tree doesn't impatiently send out blossoms on the first sunny days (only to be nipped by a late frost). During hot weather, mulch helps keep soil moisture from evaporating and keeps weeds down.
Prune Japanese varieties to an open center; others, to the modified central leader. The idea is to allow plenty of sunshine to fall on ripening fruit. Thin some of the developing fruit because most varieties set more fruit than they can support. In general, leave one fruit for every three to four inches. Don't thin Damson and prune plums.
Once trees are established, a regular feeding program can be started. Plan on about one pound of ammonium sulfate for young trees and about two to three pounds for the mature tree. Cut rate about in half for dwarf Varieties All applications should be reserved for early spring.
Insects and diseases
Black knot and brown rot can plague the plum. Spray with an all-purpose spray at petal-fall and thereafter at least three times at ten-day intervals. Wood with large, dark swellings is likely suffering from black knot and should be removed.
Harvesting
Because color varies with the type of plum, you'll have to be your own judge when it comes to determining ripeness. Fruit should detach easily with a slight twist of the stem.
