Plum

Plum is grown as a grafted, long-lived perennial tree. Commercial production spans European plum, valued for both fresh eating and drying into prunes, and Japanese plum, grown predominantly for fresh consumption, with each group having somewhat different orchard traditions and end markets.

Because plum is propagated clonally and cropped over many seasons, decisions on rootstock, species group, cultivar, and pollinizer requirements are made at establishment and shape orchard management for the life of the planting.

Family

Rosaceae (rose family)

Genus

Prunus

Principal species

Prunus domestica (hexaploid European plum) and Prunus salicina (diploid Japanese plum)

Growth habit

Deciduous tree, commercially propagated by grafting a fruiting cultivar onto a selected rootstock

The difference in ploidy between European plum (hexaploid) and Japanese plum (diploid) reflects their distinct genetic origins, and this distinction carries through to differences in typical fruit characteristics, pollination behavior, and end use between the two groups.

European plum is believed to have originated in the region around the Caucasus and Near East, while Japanese plum originated in China despite its common name, later being developed further in Japan before spreading internationally. Both groups have long histories of cultivation and selection.

Commercial production of both species groups is now established across temperate regions on multiple continents. Production statistics and leading cultivars change over time and should be obtained from primary sources such as FAOSTAT and national agricultural statistics services rather than assumed.

Plum trees require a period of winter chilling to break dormancy and flower normally; the chilling requirement varies widely by cultivar and species group. Japanese plum cultivars generally need somewhat less chilling than many European plum cultivars, though this varies enough by individual cultivar that local variety trial information should guide selection.

Spring frost during bloom is a significant climate risk for plum in many regions, since flowers and young fruitlets are frost-sensitive and damage can substantially reduce a season's crop.

Plum tolerates heavier ground than peach or cherry, and Prunus domestica in particular is grown on clay loams where a cherry planting would fail. It is still intolerant of standing water: the limit is duration rather than texture, and a site that drains slowly after winter rain is the one that loses trees.

Establishing a plum orchard begins with choosing a species group, rootstock, and cultivar combination suited to the site and target market. Pollination planning differs by group: many Japanese plum cultivars require cross-pollination from a compatible variety, while some European plum cultivars are self-fertile, though pollinizer needs should still be confirmed for the specific cultivar chosen.

• Species group selection (European vs. Japanese plum) matched to target market
• Rootstock selection for size control, anchorage, and site adaptation
• Pollinizer planning, particularly important for Japanese plum cultivars
• Training and pruning system matched to planting density

Potassium supports fruit size and quality in plum, while calcium status is linked to fruit firmness and storage quality. Boron plays a role in flowering and fruit set, which is particularly relevant where pollination is a limiting factor, as in many Japanese plum cultivars.

Plum carries a heavy crop load relative to leaf area and drops fruit when stressed, so the water-sensitive period runs from shortly after set through stone hardening. European plums destined for drying are an exception worth noting: a controlled late-season deficit concentrates sugars and is applied deliberately.

For European "prune" plum cultivars destined for drying, fruit development is managed with attention to achieving notably high soluble-solids content, a characteristic that suits these cultivars to drying and distinguishes them from plum grown solely for the fresh market.

Plum pox virus, also called sharka, is the most serious viral disease of stone fruit and the reason aphids matter more on plum than their direct feeding damage would suggest. It is spread by aphids locally and by the movement of infected nursery stock over long distances, and it is regulated: detection triggers quarantine, stop-sale and destruction rather than treatment. There is no cure for an infected tree, so the whole management effort sits in certified planting material and surveillance.

Management combines resistant or tolerant cultivars, orchard sanitation, monitoring, and — where justified — locally authorized control products applied according to their labels.

Plum is generally hand-picked at a maturity stage assessed through color, firmness, and, for prune-type European plum, sugar content suited to drying. Fresh-market fruit is typically harvested somewhat earlier than fruit destined for drying, which is often allowed to develop further before harvest.

• Fresh-market eating plums
• Dried prunes from European plum cultivars with high soluble-solids content
• Canned and processed fruit
• Juice and preserves