How to Grow Boysenberries
The boysenberries are a cross between the European raspberry, a European blackberry, an American dewberry and the Loganberry, which itself is also a cross between blackberry cultivar 'Aughinbaugh' and the European raspberry.
Boysenberries are grown in home gardens and commercially, especially in Oregon and New Zealand.
Boysenberries have large fruits, weighing around 7-8 grams (0.25-0.28 oz), with large seeds and a deep maroon/dark purple, sometimes even black color. Unripe berries are green, while yellow-reddish fruits are sour and not yet fully ripe. The boysenberries are larger than the raspberries or blackberries.
Boysenberries require plenty of sun, although they can grow in partial shade (full shade is not recommended).
They are modest plants and easy to grow, although they are not cold-tolerant as raspberries - boysenberries can be grown as a perennial bush outside up to zone 4 or 5. For colder areas, growing boysenberries in containers is one of the possible options.
Soil Preparation for Boysenberries
Regardless if they are grown on permanent position or in containers, boysenberries require slightly acidic (pH 6 is perfect), well drained soil, rich in organic matter.
Till the soil thoroughly up to one feet (~30 cm) deep - add aged or dried manure and compost/humus. If the soil is heavy some sand and compost/humus. Adding mineral (NPK) fertilizers will provide plenty of nutrients for the plants, but too much nutrients can lead to large, but weak plants, prone to diseases. Artificial (NPK) fertilizers with gradual release of nutrients are great choice, especially on sandy soils - not only for boysenberries, but for all plants commonly found in small gardens. Such fertilizers gradually release the nutrients, without overfeeding the plants or burning their roots for up to 4-6 months.
For plants grown in the rows, set the poles at the ends of the rows and tie 2-3 wires - one at 3 feet (0.9 m) and the second at 1.5 feet (0.45 m). Personally, since the boysenberries can grow tall and spread rapidly, I would recommend adding third wire at 4.5 feet (1.35 m). Of course, one can also use wire mesh or house wall or fence or ... just use your imagination and remember - full sun position, protected from the strong winds, pH around 6 (concrete walls leach lime (calcium oxide/hydroxide) and tend to increase pH over time), good drainge...
Planting the Boysenberries
Boysenberries are planted when there are no more danger of frost in the garden.
Plants are positioned 3-5 feet apart - they spread fast and easily, so if possible, give them plenty of room.
Boysenberries can be grown from the seeds or from the rooted cuttings (tip layering method).
If you need just a few plants, perhaps the best option is to buy certified seedlings from the local garden centers or from online shops.
Plants are positioned in the soil at the same depth as they were in the growing containers. Some gardeners prefer to add some aged manure at the bottom of the planting hole in order to 'kick-start' newly planted berries - this can be done, of course, but it is more important to prepare the soil in the entire row properly.
Watering the Plants
Newly planted boysenberries are watered right after planting. In order for plants to grow properly, soils should be moist, but not damp - most berries don't like 'wet feet'.
Depending on the amount of rain, boysenberries require watering once per week. Dripping system controlled via water sensors in the soil is excellent choice, but often an overkill for the home gardeners - when watering other plants in the garden, water the boysenberries, too. Without enough water, boysenberry crop is reduced, and the fruits are not as tasty and juicy as when the plants are watered regularly.
When watering the plants, be sure to keep the leaves dry - wet and moist leaves and branches can lead to mildew and mold.
Maintaining and Pruning the Boysenberries
Plants are grown upright - tie the canes to the wires once they grow tall enough. The boysenberries cling to the wire and expand outward along it - hence the need for third or even fourth wire. When growing the berries along the walls, fences or when using wire mesh, tie the plants as needed.
Boysenberries produce their fruit on one year old canes, so the plants have to be pruned accordingly. The easiest method is to remove the canes that have already been harvested. These canes will not bear the fruits any more, but require water and nutrients, and perhaps the most important, they can be very thorny and thus annoying when picking the berries.
New, healthy canes which grow during this year are the ones that will bear fruit the next year and having them strong and healthy means that next year harvest will be at least as successful as this one.
Twice a year, in the autumn and in the spring, add aged/dried manure and some compost/humus into the soil. If the plants are not growing as expected in the spring, check the nutrients' levels and if required, add balanced NPK fertilizer with microelements (Fe, Mg, Cu, Mn ...).
Mulching the soil decreases the moisture loss and prevents the weeds from growing on the patch. Also, as the mulch slowly decompose, it also feeds the plants and keep the soil slightly acidic.
Harvesting the Boysenberries
Depending on the location and variety, harvest time is generally in July and August.
Boysenberries are harvested in the morning when they are fully ripe (dark purple) - if not sure, taste them.
Boysenberries are relatively large berries, they taste very good, they are very healthy, but they don't last very long when harvested.
Personally, they should be consumed or processed the very same day when they were harvested. When kept in the refrigerator, they can last for few days, but not more.
Single mature, well kept plant can produce up to 10 pounds of fruits during one season.
Pests and Diseases
Birds like boysenberries, just like people do :) To prevent the birds from stealing your tasty fruits, bird protective netting should be used to cover the plants.
Diseases that attack raspberries or blackberries can affect the boysenberries, too.
To prevent the mold and mildew, plant the boysenberries on sunny positions, don't get leaves wet when watering the plants, and remove old canes - well aerated bush is great prevention from such diseases.
When the leaves and branches showing symptoms of diseases (gray spots and patches, dying canes and branches), immediately remove all problematic leaves and canes and use fungicides to prevent the issues from spreading around.
Some gardeners use water soluble fungicides before any disease occur, especially in the mixed gardens.
Whatever you do, be sure to read and understand the instructions/manuals of any chemical you use in your garden.
Growing Boysenberries in Containers
Boysenberries can be grown easily in larger containers or flower pots.
For a single boysenberry plant, 18 inches wide and 12-14 inches deep flower pot is required.
After making several drainage holes, fill the container with good, slightly acidic potting soil, rich in organic matter and nutrients.
Plant the boysenberry seedling in the middle of the container and set several thin poles along the edge of the container - connected these poles with wire, effectively creating the cage where your boysenberry will grow.
Since the containers have limited volume, add fertilizers more often and water regularly - during hot summer days, water every or every other day.
In the smaller containers, keep number of canes limited - 5 to 7. In larger pots, for example 30 inches wide (~76 cm) and 20 inches (~50 cm) deep, plant 2-3 boysenberry plants and keep total amount of canes to 10-15.
Note: when growing berries of this type in containers, gardener must be more 'aggressive' when pruning the plants ...
Growing boysenberries in containers is highly recommended in colder areas and in smaller gardens. Don't forget, they are also very decorative plants.
Long Story Short - Boysenberries are excellent berries for small gardens. They are easy to grow, not very picky about the soil, water and nutrients, just be sure that they grow on sunny positions and prune them as required.
And when harvested, these berries are not kept well, so when harvested - eat them right away :)