Contents

1.1 Description of the Plant

The “Blue Plum” is a richly coloured selection of European plum (Prunus domestica), celebrated for its deep indigo skin, amber flesh, and high sugar content—perfect for fresh eating, preserves, and drying into prunes. A moderately vigorous, deciduous tree, it matures 3–5 m tall on semi‑dwarf rootstock (6–7 m on seedling rootstock), forming a broadly oval crown. White, five‑petalled blossoms open in mid‑spring before leaf‑out, dazzling bees and other early pollinators. Fruit ripens late August to mid‑September in Ontario, oval to oblong (35–45 mm), with a naturally waxy bloom and a freestone pit that separates cleanly.

1.2 Historical and Cultural Context

European plums trace back to ancient Silk‑Road hybridisations of cherry plum (P. cerasifera) and sloe (P. spinosa). By Roman times they were prized across the empire; Benedictine monks later spread improved cultivars throughout mediaeval Europe. Blue‑skinned “prune” types arrived in North America with 18ᵗʰ‑century German immigrants, thriving in the Great Lakes region. Their reliable self‑fertility, cold hardiness (to –30 �C), and ease of drying made them the homesteader’s plum of choice.

1.3 Edible, Medicinal, and Useful Properties

Edible:

• Fresh fruit: 80 % water, 10 % natural sugars, rich in vitamins A & C and antioxidant anthocyanins.
• Drying: Converts to sweet prunes at 18–20 % moisture—ideal winter caloric store.
• Culinary: Excellent for jams, sauces, wine, and fermented plum vinegar (ume-su style).

Medicinal & Utility: Prunes are gentle natural laxatives (soluble fibre + sorbitol). Fruit skins yield a pale purple dye. The dense, fine‑grained wood polishes well for turning and instrument parts.

Ecology: Early blossoms provide a vital nectar source; ripe windfall plums feed birds and pollinator larvae.

4 Planting Outdoors

1. Site Selection — Full sun (6 h day); well‑drained loam or sandy‑loam, pH 6.0–7.0. Avoid frost pockets.
2. Spacing — 4–5 m between semi‑dwarf trees; 5–6 m for seedling‑rooted standards.
3. Soil Preparation — Loosen top 40 cm; blend in 5 cm compost plus 1 kg rock phosphate per planting hole.
4. Pollination — Most blue/prune plums are self‑fertile; nevertheless, yields improve 20–30 % with a second European plum cultivar nearby (within 25 m).
5. Companion Planting — Under‑plant with nitrogen fixers (clover, comfrey) and insectary herbs (mint, yarrow) to attract beneficials.

5 Ongoing Plant Care

1. Watering — 15–20 L weekly through dry spells for first 2 years; mature trees need 25 mm rain equivalent per week during fruit swell.
2. Mulching — 8 cm wood chips, leaving 10 cm clear of trunk; renew each spring.
3. Fertilisation — Early spring broadcast 120 g balanced organic fertiliser per trunk‑diameter cm (DBH). Excess N raises black‑knot risk.
4. Pruning — Late winter: shape to open‑centre (vase) or modified leader, remove water‑sprouts, and thin to 4–5 main scaffolds. Summer tip‑prune for size control.
5. Pest/Disease — Monitor for plum curculio and black knot. Pick up windfalls, prune out knots 15 cm beyond infection, and compost hot or burn.

6 Harvesting and Storage

• Harvest Window: Fruit detaches with a gentle twist when background colour turns from greenish to amber; soluble solids > 18 �Brix.
• Fresh Storage: Store at 0–2 �C, 90 % RH for up to 3 weeks.
• Drying: Halve or leave whole, dry at 60 �C until leathery (12–18 h); final moisture ≈ 20 %.
• Freezing: Halve, pit, flash‑freeze on trays, then pack into containers for up to 12 months.

7 Propagation

• Grafting: Whip‑and‑tongue scion grafts onto Myrobalan or Krymsk 1 rootstock in early spring.
• Seed: Possible but variable; requires 90 days cold stratification.

8 Recipes and Uses

Baked Honey‑Plum Crisp:

Combine 1 L sliced plums, 60 mL honey, 5 mL lemon juice; top with 250 mL rolled oats mixed with 60 mL melted butter, bake 180 �C 40 min.

Plum Butter:

Simmer 1 kg pitted plums with 125 mL maple syrup and 5 mL cinnamon until thick; pur�e and water‑bath can 15 min.

Pressure‑Steamed Plums:

Add 250 mL water to cooker, rack, load 1 kg halved plums in jars; high pressure 5 min, natural release 10 min—perfect pie filling base.

9 Summary

Blue Plums combine Old‑World heritage with modern reliability—self‑fertile, cold‑hardy, and richly flavoured. Whether eaten fresh, dried as prunes, or cooked into preserves, they bring a burst of late‑summer sweetness to Ontario orchards and food forests. Plant a pair (or more) to enjoy decades of blossoms, shade, and indigo harvests.