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Growing Blackberries and Boysenberries: Rubus ursinus

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Overview
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.

Description
Form: A bramble, composed of canes growing from a root crown.
Lifespan: Productive for 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 fruit 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. The berries are ripe when fully black. They are sweetest when they turn from glossy black to dull black.
Storage after harvest: Blackberries 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. The first year canes (primocanes) produce leaves with no flowers or fruit. Second year canes (floricanes), produce flowers and fruit on their lateral branches. A few cultivars, however do produce flowers in the fall on the top one-third of their first-year canes. These primocane-blooming cultivars do not as yet perform well in high temperature regions.
Roots: Shallow, spread 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, its 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) The thorns are so numerous, narrow and sharp that it is exceedingly painful to grow this plant. Even thick gloves may not prevent punctures and pain. Large, sweet, firm berries, early ripening, erect canes, USDA Zones 6-10. This is the most productive and hardy of all blackberry cultivars grown in Arizona.
Wildlife: Attracts bees, birds and small mammals that eat the fruit. Blackberries are caterpillar host plants for the Blackberry Looper moth. Rabbits also like to eat the canes and bark, so this plant may need a rabbit-proof enclosure.
Toxic / Danger: Many cultivars are thorny to very thorny.
Origin: Northern Hemisphere non-desert regions in Asia, Europe, and North America.

Cultivation and Uses
USDA hardiness zones: 5-10 or 6-9 for cultivars suitable for hot dry climates.
Chill hours: Depends on the 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 do not flower or set fruit in warm winter regions.
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 a 4' diameter. Blackberry roots are shallow, not deep. The plant needs water twice a week in temperatures over 100°F or the canes will die back to the roots. It will recover from its roots when rain begins.
Soil: Well drained, with pH 5.1-7.5 (strongly acidic to neutral). Place in a hole at least one foot deep, with a 4' diameter, containing 20% organic material.
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. Avoid low areas where freezing air can pool and damage crops.
All canes are easier to harvest if they are held in a fan-shaped arrangement off the ground by horizontal wires between posts.
First Year Care: Frequent watering is critical to establish an extensive root system.
Pruning and Weeding: Remove suckers more than 2' from the base of the plant. In the summer, using pruning shears, trim off the last 4" of primocanes to encourage side branching and more flowers. After harvest, cut the second year canes that have just produced fruit to the ground.
Remove weeds and grass, 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: Blackberries are very susceptible to Verticillium wilt. Avoid planting them 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.

Comments
Because nurseries may 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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