How to grow Boysenberry

Where to plant

Plant in full sun in rich, well drained soil with plenty of compost worked in. Oregon State notes trailing blackberries are the least cold hardy and least heat tolerant type, and OSU rates Boysen for zones 6 to 9. They crop best in Northern and Southern California and the Pacific Northwest west of the Cascades.

They also grow in North Florida, the Gulf South, Texas, the Mid-South, the Mid-Atlantic and the Southern Plains. In zone 6 parts of the Northeast, Midwest and Mountain West, lay the canes on the ground and mulch them for winter. The Northern Plains and Alaska are too cold, Central and South Florida lack the winter chill, the low desert is too hot and dry, and in Hawaii escaped blackberries are serious weeds, so do not plant them there.

Choosing a variety

Buy certified, disease free plants from a reputable nursery, rather than digging suckers from an old patch, which can carry viruses and other diseases. Thornless Boysen clones are easier to handle, though OSU notes they may revert to thorny canes over time; cut out any thorny canes that appear.

How to plant

1. Plant dormant canes in winter in mild areas, or in spring as soon as the soil can be worked in colder ones, keeping the roots moist until planting.
2. Set plants at the depth they grew in the nursery, 3 to 5 feet (1 to 1.5 m) apart along a trellis.
3. Build a trellis with two wires, the top one about 5 feet (1.5 m) high, before the canes grow long.
4. Cut the canes back to about 6 inches (15 cm) at planting, then water in well and mulch.
5. In the first summer, tie new canes to the trellis as they grow. These will fruit the following year.

Watering and feeding

New plants have small root systems, so water several times a week at first, wetting the root zone without leaving standing water. Established plants need about 1 to 1.5 inches of water a week through the growing season, wetting the soil 6 to 12 inches (15 to 30 cm) deep each time. Drip irrigation is ideal because it keeps the canes dry and reduces disease.

Feed with a balanced fertilizer in early spring as growth begins, at the label rate. A mulch of compost or bark around the plants holds moisture and keeps weeds down.

Pruning and care through the year

• Each year new canes (primocanes) grow from the crown while last year's canes (floricanes) fruit on the trellis. Bundle the new canes along the ground under the trellis as they grow, so they are out of the way.
• Right after harvest, cut every cane that fruited off at the crown, taking care not to cut the green new canes.
• Then train the new canes onto the wires, splitting them into two bundles and wrapping them along the trellis. They carry next year's crop.
• In colder or exposed gardens, leave the new canes bundled on the ground through winter under mulch, and lift them onto the wires in late winter before buds break.
• Cut out any thorny canes that appear on a thornless plant.

Harvesting

Boysenberries ripen early in the blackberry season, from about June in California to late June through early August in the Pacific Northwest. Pick when the berries are dark maroon, plump and come away easily, every two or three days.

The berries are soft and do not keep long, so refrigerate them straight away and use them within a couple of days. They freeze well and make excellent jam and pie.