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Growing Blackberries and Boysenberries: Rubus ursinus

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A Rose family member, the Rubus genus has over 250 species. Commercial blackberries in North America are hybrids of several blackberry species, including Rubus laciniatus, the European Evergreen Blackberry. Rubus ursinus, the native blackberry of the North American Pacific Coast, is used as a base for heat tolerant blackberries.

Form: Canes growing from a root crown, called a bramble.
Lifespan: Productive 15-20 years.
Leaf retention: Deciduous.
Growth rate: Rapid.
Mature Size: 10' high and as wide.
Flowers: White, five petals.
Bloom: Late winter to early spring.
Self-fruitful: Yes.
Years before fruiting: 0-1.
Fruit: The "berry" is an aggregate fruit, with many small round fruits clustered together, connected to a center part called the torus. Seeds are relatively large. Blackberries do not ripen if picked unripe.
Months for fruit to ripen: 1-1.5, depending on cultivar. Ripe when fully black. Berries are sweetest when dull black instead of glossy.
Storage after harvest: Blackberries have a short shelf life. They can be refrigerated up to 7 days. But then must be eaten, cooked or frozen immediately.
Leaves: Dark green, fuzzy, toothed edges, small spines underneath.
Stems: Blackberry canes fall into four groups based on whether they are thorny or thornless and erect or trailing. Erect canes are somewhat self-supporting while trailing canes need to be trellised. Flowers normally bloom on second-year canes (floricanes) but a few cultivars also produce flowers in the fall on first-year canes (primocanes). Primocane-blooming cultivars do not as yet perform well in high temperature regions. All stems are easier to harvest if they are held in a fan-shaped arrangement off the ground by horizontal wires between posts.
Roots: Shallow, spreads by rhizomes, invasive in moist areas, but sensitive to heat in USDA zones 8 and up.
Cultivars of Note for hot regions:
'Boysenberry Thornless' (Rubus ursinus x idaeus), very large, delicious, fragile, purple berry, few seeds, harvest throughout summer, trailing canes need support, 250-350 chill hours, USDA zones 5-10.
'Ouachita' [pronounced WASH-i-ta] (Rubus ursinus) thornless, large, sweet, firm berry, mid- to late-season ripening, erect canes, 200-300 chill hours, USDA Zones 5-9. High yields in temperatures under 100°F.
'Rosborough' (Rubus ursinus) Very thorny, large, sweet, firm berry, early ripening, erect canes, USDA Zones 6-10. The most productive and hardy in Arizona of all blackberry cultivars.
Wildlife: Attracts bees, birds and small mammals that eat the fruit. A caterpillar host plant for the Blackberry Looper moth. Rabbits also like to eat the stems and bark, so this plant may need a rabbit-proof enclosure.
Toxic / Danger: Many cultivars are thorny.
Origin: Northern Hemisphere: non-desert regions of Asia, Europe, North America.

Cultivation and Uses
USDA hardiness zones: 5-10 or 6-9 for cultivars suitable for hot dry climates. Avoid low areas where freezing air can pool and damage crops.
Chill hours: Depends on cultivar. Plants needing 100-300 chill hours are best in USDA hardiness zones 8-10. Many cultivars found in nurseries need 500-1000 chill hours and will not flower or set fruit.
Heat tolerant: Needs afternoon shade when temperatures exceed 100°F.
Sun: Full sun to part shade. More sun means better fruit production, but berries can be sunburned without sufficient leaf shade.
Drought tolerant: Yes.
Water after becoming established: Every two weeks without berries, once a week during berry production. Water evenly in a circle around the base of the plant up to 4' diameter. Blackberry roots are shallow, not deep. Needs water twice a week in temperatures over 100°F or stems will die back to roots. It will recover from roots when rain begins.
Soil: Well drained, at least one foot deep, loose to 4' diameter with 20% organic material, pH 5.1-7.5 (strongly acidic to neutral).
Fertilize: After the first year, use an organic fertilizer, spread in a three-foot circle around the plant, in early March and early July.
Mulch: Use 2-4" of organic material around shallow roots.
Spacing: Plant 3-4' apart in rows 8-10' apart.
Planting: In USDA zone 9 and up, plant in the fall instead of winter or spring. Summer heat will inhibit root formation.
First Year Care: Frequent watering is critical to establish an extensive root system.
Pruning and Weeding: Remove suckers more than 2' from base of plant. After harvest, cut the floricanes (2nd year canes that have just produced fruit) to the ground. In the summer, using pruning shears, trim off the last 4" of primocanes to encourage side branching and more flowers. Training to a high fence or horizontal trellis four feet above ground makes harvesting easier.
Remove weeds, which compete for nutrients, by hand to avoid damage to shallow roots. No other vegetation, especially grass, should be growing within 4' of the base of the plant.
Litter: Low.
Propagation: Leafy cane cuttings, suckers cut from roots, root division.
Pests: Very susceptible to Verticillium wilt. Avoid planting in soils where previous plants had that disease. Nightshade family members and some rose family members are susceptible, so avoid soils where they have grown.
Uses: Edible fruit.

Because many nurseries do not carry cultivars suitable for hot desert regions, consider ordering online.

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Blackberries and Boysenberries: Rubus ursinus - flowers

Blackberries and Boysenberries: Rubus ursinus - fruit

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