The blackberry brings to mind wild black and tasty berries which are well protected by their prickly shrubs. Nowadays, thanks to breeding efforts of different growers, we have many thornless varieties which yield giant and tasty berries, and can easily be cultivated in home gardens and on commercial plantations.
The blackberry cultivars originated from hybridizing several morphologically differentiated botanical varieties. One of the main groups includes varieties with elevated stems, such as American Rubus argutus and R. Fructicosus and R. procerus native to Europe and Asia Minor. The other group contains botanical varieties with trailing stems, such as European R. caesius and R. Hirtus, and American R. ursinius and R. flagellaris. Nowadays, breeding efforts are directed towards obtaining thornless cultivars which make berry picking easier, are resistant to diseases, yield abundant crop, bear big and tasty berries, are transport tolerant and have long shelf life. In Poland, the blackberry is a wild shrub which can often be seen growing in forests and in brushwood.
Blackberries develop leaves along the whole length of stems. They are serrated, palmate or digitate, and their blades possess distinct venation. Some blackberries, apart from thornless varieties, develop prickles along their stems.
They usually display five-petal, androgynous flowers, gathered in clusters or panicles, which are mostly white or pink with many free stamens and pistils; they are usually scentless but melliferous, attractive for pollinators which swarm into them.
Blackberries are black, one-seed drupelets, joined in a spurious fruit filled inside with a big receptacle. Blackberry fruits boast antiinflammatory, antibacterial and antiviral characteristics since they contain many vitamins (vitamin C – 21mg/100g, which covers 60% of a daily requirement for ascorbic acid, and vitamins A, E, K, B1, B2, B3 and B6, as well as folic acid) and minerals (calcium, iron, magnesium, phosphorus, potassium, sodium and zinc). Thanks to their high content of antioxidants, they protect the body against destructive effects of reactive oxygen species. They contain carbolic acids and ellagic acid, and possess higher anthocyanin content than raspberries. Blackberries accelerate metabolism and that is why they are an ingredient desired in slimming diets and they are also a good supplier of pectins, i.e. soluble fibre (5.3 g in 100 g). A glass of blackberries covers 30% of a daily requirement for dietary fibre which limits absorption of unhealthy fats and indirectly reduces the risk of heart diseases. Blackberries belong to food products with a low glycemic index (GI=25) and have only 43 kcal in 100 g, which means that they can be eaten by diabetics.
Blackberries prefer fertile and slightly acidic soils (approximately pH 6.0) which cannot be too compact and impermeable, because they do not develop well either in water catchment areas (even for a short time) or places with high level of groundwater.
Blackberries thrive best in sunny or partly shadowed and sheltered positions.
The blackberry species possess different cold hardiness and that is why it is best to choose the cultivar which is tolerant of the climatic conditions in a given region. In autumn, before entering dormancy, they do not like low temperatures and they do not tolerate temperature changes in early spring either, especially periods of warmer weather followed by the return of winter.
• irrigation water
Blackberries are tolerant of temporary drought since their roots grow slightly deeper than in raspberries; however, it cannot be too long because otherwise it will adversely affect their development and crops. In order to secure them the best possible conditions it is recommended to irrigate plantations especially in permeable and light soils.
• soil preparation
Soil for the blackberry cultivation should be prepared in a similar way as for the raspberry cultivation (see: Raspberry, Cultivation). In short, it consists in weeding the positions, obtaining the optimal soil pH value and supplementing it with indispensable nutrients, according to the soil analysis results conducted beforehand.
Early spring is the best time to set up a blackberry plantation, but it is also possible to do it in autumn; however, young plants should be sheltered against frost then. Seedlings grown in containers can be planted throughout the whole vegetative season but special precautions should be taken to protect them against drought, especially when the temperature is high. Blackberry seedlings should be planted slightly deeper than they used to grow in the nursery (approximately 3–4 cm). Soil around a newly planted seedling should be compressed. The planting spacing in a row of varieties which fruit on biennial stems depends on the way of the shrub training and the vigorous growth of the cultivar, which may differ from 1.0 m to even 3.0 m. The varieties with climbing and trailing stems require greater spaceing between plants, since they have to be spread on supports, than those with an elevated habit. When planting the cultivars fruiting on annual stems, a minimum spacing of even 0.5 m between the plants should be kept but the spacing for pot plants may be slightly smaller. The spacing between rows depends on the machinery used; the smallest spacing may equal 1.8 m. The greater the spacing between the rows, the worse the crop, but nurturing and harvesting are easier. The optimum spacing is 2.5–3.0 m.
Fertilizing – not only in the case of blackberries – should be based on the soil analysis and its supplementation with appropriate nutrients, according to the recommendations attached to the analysis results. General fertilizing recommendations are similar as in raspberries (see: Raspberry, Cultivation).
Proper weeding is a basic treatment conducted before setting up a blackberry plantation and during its vegetative season. On commercial plantations, spaces between rows are most often hay-growing fallow or a herbicide fallow.
The blackberry pruning and shaping depends on its variety and the way of fruit bearing. Those fruiting on biennial stems in the first year are trained in such a way that only several main stems are left and spread on supports. In their second year, in early spring, the main stems should be shortened at the height of 1.70 m, and the lateral shoots left 30–40 cm long. After some time, buds turn into fruit bearing sprouts which bloom and give fruits. Once the harvesting has been completed, those sprouts should be cut off at the ground and at the same time the number of one-year old sprouts should be diminished and five to seven of them should be left.
Blackberries fruiting on annual stems are usually grown as single shrubs, so their pruning consists only in limiting the number of stems. In autumn, after harvesting, all stems are cut out close to the ground, and in spring new ones appear and give fruits.
Blackberries are most often picked by hand. They should be harvested at the right time, and their colour cannot be the only indication of their full ripeness. When harvested too early, despite proper hue, they are sour and not tasty. Blackberries reach full harvesting ripeness when they come off the stem easily. When harvested too late, they are unfortunately extremely perishable and not transport tolerant. After harvesting, they should be chilled down to +2oC or +5oC as soon as possible.
DISEASES AND PESTS
The blackberry plantations are sometimes attacked by gall mites (out of which the redberry mite – Acelitus essigi, is the most dangerous), spider mites, acari or weevils. To the most dangerous diseases belong those which cause fruit rotting, mainly fungal diseases. The general health of the plantation is one of the decisive factors for obtaining good crops and it is best to consider it already when purchasing healthy nursery plants. The incidence of pathogens during cultivation should be fought by accessible agents, recommended by a current plant protection programme.
Blackberries can be enjoyed raw (especially table varieties) or can be added to various desserts (e.g. fruit salads, cakes, ice-creams or jellies). They are also good for commercial processing into jams, juices, and wines and fruit liqueurs and into individually quick frozen fruit. Thanks to their intense colouring they can dye different dishes and fruit preserves.
In traditional folk medicine, the blackberry juice was used for colds, infections and in order to strengthen general health. The blackberry leaves extract was used to fight fever and flue while the leaves infusion to fight diarrhea. Blackberries cleanse the body of toxic substances, positively affect the functioning of the digestive and circulatory systems, and are used as a prophylactic measure against eye diseases and cancer; moreover, their content of vitamin K improves bone thickness. They also boast soothing properties and are recommended in nervous disorders prevailing during menopause. Blackberry juice was recommended for compresses against eczema and lichens.
J. Danek, Uprawa maliny i jeżyny, 2014