The boysenberry combines the flavor and properties of the raspberry and blackberry. Here’s how to plant, care for, and harvest the soft fruit.
The boysenberry (Rubus loganobaccus) is a soft fruit from the rose family (Rosaceae). It is an American cross between the blackberry and loganberry (Rubus x loganobaccus). The loganberry itself is a cross between the (Rubus idaeus) and the North American blackberry (Rubus ursinus), or more precisely the ‘Aughinbaugh’ blackberry and the ‘Red Antwerp’ raspberry. It was created in 1881 in the garden of the Californian judge J.H. Logan. Rudolph Boysen then crossed the loganberry with a blackberry around 1920 in California – this produced the boysenberry. As a result, the genes of the blackberry are better represented in this fruit species than those of the raspberry. The berries are grown on a large scale in the USA and in New Zealand.
The boysenberry is a fast-growing, semi-upright and not very frost-hardy shrub which forms strong, thornless canes. It grows to a height between 3 and 6.5 feet. The medium green leaves are alternately arranged with slightly serrated margins. From May to August, flowers appear in clusters at the end of shoots and side shoots. The two-year-old shoots produce deep reddish-purple, soft, aromatic fruits that are two to three times bigger than blackberries and up to 0.28 ounces in weight. From a botanical perspective, they are not berries in the true sense of the word, but aggregate stone fruits, as each drupelet has its own seed.
The boysenberry thrives in sunny locations where the fruits can mature well and develop their aromatic taste. Boysenberries are relatively undemanding when it comes to soil quality, but the best soil is rich in humus and permeable. Heavy soils are less suitable for cultivation.
As the boysenberry is quite sensitive to frost, it is advisable to plant it in spring, in April or May. To get the plant off to a good start, you can work a little decomposed manure into the soil. Just like with blackberries, you can grow the fruit on trellises or wires. Put the container plants around four inches deeper than they were in pots so that the new basal shoots can be formed. Make sure to leave a gap of around 6 foot between plants. Cut the existing shoots back to a length of around 12 inches and then water the plant well.
The boysenberry does not require much further care. Simply give the plant some compost (one to two liters of mature compost per square meter) in spring. Water the plant evenly, especially when the fruit is ripening and during dry periods. Mulching with grass clippings conserves water and heat.
Boysenberries can be grown and pruned in a similar way to blackberries. It is advisable to tie the canes to a three to five row wire trellis, splaying them out in a fan shape. The side shoots that form in the leaf axils can be trimmed by around a hand’s width in September. In late winter, they can be cut back to leave just two or three nodes. The shoots that produce the fruit will develop here during the second season. After the harvest in fall, the canes that produced the fruit should be cut back close to ground level. You should also remove weaker shoots, leaving only around six to eight of the stronger canes each year.
Just like blackberries, the boysenberry is self-pollinating.
Boysenberries are ready to harvest from early August to September. The berries, which are rich in vitamins, have a slightly tart flavor when they are dark red and soft, and can be easily removed from the branch. Freshly picked boysenberries make for a great snack, they can also be used to make jams and marmalades or to refine cakes, desserts, and fruit yoghurts. As the ripe fruits are very sensitive to pressure, the berries should be used quickly.
Boysenberries are not particularly frost-hardy, so it is advisable to leave leafy canes on the plant over winter. You can also provide the plants with winter protection by covering them with straw or brushwood mats.
You can propagate boysenberries in a similar way to blackberries: Cut a few canes off the plant in winter and trim them to a length of around 7.87 inches. Then simply put them in a new spot in the garden.
Like other species of berry, the relatively robust boysenberry is particularly susceptible to diseases such as downy mildew and in wet years.