The plant is a stone fruit, so called because it has a pit; it’s closely related to cherries, almonds, peaches and apricots, which all share the botanical name Prunus. The main species of plums are as follows:
Native plums Most are very hardy and bear juicy fruit of variable sweetness or tartness. You’ll need more than one cultivar, as the trees are not self-pollinating.
The species include Canada plum (P. nigra) and American plum (P. americana); both are native to eastern and midwestern North America as far northwest as Saskatchewan, and bear small yellow to red fruit. While the two are similar, American plum fruit is partially coated in bloom (the whitish powder that gives plums their waxy appearance). The tree is also very thorny and tends to sucker and form dense thickets. The Canada plum has shiny skin, and some cultivars are thornless. It’s more upright and treelike, usually with a distinct trunk. Both species can reach six to nine metres tall and are hardy to Zone 3; selected cultivars survive to Zone 2. Among the hardiest are ‘Dandy’, ‘Mammoth’ and ‘Norther’ (they’ll resprout if they die back to the ground during a harsh winter), though ‘Bounty’ may be the hardiest plum of all, to Zone 1.
European plums Not closely related to other plums, these can’t be crossed with other species. Plums of European origin have very sweet, firm flesh and are freestone (the flesh doesn’t cling to the pit). Many are considered self-pollinating, but you’ll usually have better fruit production if you grow more than one cultivar.
By far the most commonly grown species is P. domestica, which reaches five to six metres tall. It’s the most popular of all the plums grown in home gardens in Canada, despite its limited hardiness (most are Zone 5) and poor disease resistance. These are the smaller, purple-skinned, oval plums most commonly found in supermarkets, although there are also yellow cultivars. Fortunately, hardier types have been developed, making it possible to grow European plums in Zone 4. Among the latter are such popular varieties as ‘Mount Royal’ and ‘Reine Claude’.
The other European species is the damson plum (P. insititia), with smaller, tarter fruit produced on a 10-metre-tall tree. It’s possibly the best plum for preserves, but few damsons are hardy below Zone 5. The ones grown in Canada are mostly varieties imported from Europe generations ago, such as ‘Mirabelle de Nancy’ and ‘Damson’.
Japanese plums P. salicina is, in theory, the least hardy species—suited to about the same climate range as peaches (Zone 7, or possibly 6)—but there are now much hardier selections of this eight-metre-tall tree available, some even to Zone 3. They’re the large, red-skinned plums on the supermarket shelves with the oh-so-juicy red or yellow flesh, although some have yellow or black skin. Some of the hardiest are ‘Brookgold’ (Zone 2), ‘Shiro’ (Zone 3) and ‘Tecumseh’ (Zone 3). Japanese plums are not self-pollinating, so two cultivars will be needed.
Hybrid plums They’re also known as Japanese-American plums, which better describes their origins. They combine the features of both species: the larger fruit of the Japanese and the hardiness of the native. There are nearly 50 cultivars available, so the choice is vast. Hybrid plums have one major flaw, though: they’re not self-pollinating and are poor pollinators. Even planting two different cultivars side by side won’t help much. For good production, you’ll need to grow a native plum as well. Here are a few of the hardiest hybrids: ‘Patterson’s Pride’ (Zone 2), ‘Perfection’ (Zone 2) and ‘Superb’ (Zone 2b).