Rubus idaeus L.
Raspberries are not only tasty but also highly regarded for their nutritional values. These delicious and aromatic berries are a treasury of vitamins and minerals. They are considered to be a natural home remedy for colds and flu, and are good for the fresh fruit market and for commercial processing. Raspberries are rewarding plants since they yield a potentially profitable fruit crop in a short time (the plantation set up in spring yields the first crop already in autumn). The raspberry cultivation does not cause many problems and, taking into account proper selection of varieties, one may enjoy fresh fruits from early summer to late autumn.
In the wild, the raspberry grows almost everywhere in Europe and partially in Asia. It prefers various habitats and can be found on the forest edges, on mountain slopes and in the meadow thickets. Raspberries currently cultivated in home gardens and on plantations belong to the species of the red raspberry which originated from the proper raspberry (Rubus idaeus L.) of the European R. idaeus vulgatus and American R. idaeus strigosus ecotypes. While hybridizing new cultivars, breeders use also other raspberry species. The varieties of the yellow raspberry, which belongs to the red raspberry group, are becoming more and more popular due to their original colour. Sporadically, in domestic and commercial cultivation, one may see varieties of the black raspberry which originated from R. occidentalis. It boasts not only distinguishing black fruits, but also a different way of propagation (by tip layering) – its berries are borne on biennial stems. The purple raspberry is a curiosity. It is a cross-breed of the red and the black raspberry and boasts their indirect features, but it is not cultivated in Poland.
Raspberries develop three, five or seven-lobed, sharply serrated leaves which are hairless on top but underneath with a white hairy covering, their leaflets are sessile; those on the fruiting stems are always three-lobed (it does not apply to new varieties which bear fruit on first year canes).
They display white flowers, gathered in loose clusters or panicles, which can be a major nectar source for honeybees and other pollinators.
The raspberry fruit consists of many small hairy red (less often yellow or black) drupelets, each of which consists of a juicy pulp and a single central seed, gathered in an aggregate fruit which contributes to raspberry’s nutritional value; when ripe they easily drop off the receptacle. Raspberries contain approximately 85% of water, 1.3% of protein, 0.3% of fat, over 8% of carbohydrates, 5.3% of dietary fibre, 0.5% of minerals, 2% of organic acids (among others citric, apple, amber and wine acids). Apart from vitamin C, they are also rich in vitamins A, E, K, B1, B2 and PP, folic acid and such volatile substances as alcohols, aromatic aldehydes, inositol and lecithin, and also antocyan pigments.
Raspberries also have a high content of antocyans and compounds which belong to the group of poliphenoles. It has been proved that they possess antioxidant (anti cancer) properties. Ellagic acid, which is also present in raspberries, boasts similar characteristics; it protects against cancer and manifests antibacterial and antiviral qualities. Raspberries are a respectable source of such chemical compounds as iron (haemoglobin ingredient) or magnesium (regenerates the nerve fibres).
Most often traditional, cultivated varieties of raspberries bear fruit on biennial stems from July to August. In the first year, barren (not fruiting) stems grow from the root neck or from the adventitious buds and in the following year they bud into the fruiting canes. After the fruit bearing period, the whole stems die.
More and more often one can meet raspberries which repeat fruit bearing (double or everbearing), and in their case harvesting lasts from June until the autumn ground frost. Already in the first year, before stems finish growing, in their upper parts they develop flowers and set fruits which ripen in late summer and in autumn of the same year. The longer or shorter fruiting part of the stem dies, but the buds which sit below bear fruits the following year in a usual fruit bearing period (July/August).
Raspberries thrive in fertile soils, rich in nutrients, slightly acidic and well drained but not too sandy. They grow best in flatland or on gentle south-east or south-west slopes and prefer positions sheltered against strong winds, which adversely affect their fruit development and contribute to frostbite in winter. It is rather not recommended to set up plantations in frost hollows or on floodplains (even for a short period of time), not mentioning the places where ground water comes too high, because it can be as harmful as drought.
Raspberries need ample sun for optimal development.
Most currently grown raspberry varieties are cold hardy.
• irrigation water
Raspberries are moisture demanding since they are rooted rather shallow. Irrigation is especially important when their fruits develop and ripen, lack of water at that time results in smaller fruits and a worse crop. It is best to install an irrigation system (e.g. a dripline irrigation system, which – as opposed to irrigation sprinklers – does not increase the danger of disease attacks on canes and fruits).
• soil preparation
Soil preparation for the raspberry cultivation has key importance for successful crops. Brassicas (plants of the cabbage family), rape and bulb and root plants (excluding potatoes, which may increase the prevalence of the root system diseases, and cereals) are a good forecrop for raspberries. First of all, one should conduct an effective weeding since doing it on the already existing plantation is labour and time consuming and sometimes even impossible to carry out without partially destroying the plants. Soil preparation also includes organic and mineral fertilization. In order to increase the soil organic content it is best to amend it with ample organic matter in the dose of 40–50 t/ha, several weeks prior to planting raspberries. Instead of manure, one may also use green plants used for ploughing (mustard or phacelia), substances enriching humus or humus acids and effective microorganisms. Mineral fertilization should be preceded by the soil analysis including its content of nutrients (its results are accompanied with recommendations on the type and doses of fertilizers). One should also not forget about the soil pH, e.g. alkaline pH > 8.0 is not adequate for raspberry cultivation. The best soil pH should fall between 5.5 and 6.5. In Poland, most soils are acidic and require liming, which should rather be done not just before planting raspberries but a few weeks earlier (e.g. before forecrop or first ploughing).
Raspberries should be planted in late autumn or early spring, but it is best to plant them in autumn due to better soil moistness. Spring planting is recommended only in areas with severe winters to avoid frostbites, especially if winters are without snowfalls. However, one should bear in mind that shrubs planted in spring require more abundant irrigation.
Raspberries should be planted shallow, best 2–3 cm deeper than they grew in a nursery. After planting, compress the earth round the plants to help water permeate and irrigate them abundantly. If shrubs are planted in autumn, they should be mulched in order to protect their root system against frostbites.
Raspberries are most often planted in rows, every 0.5 m. The spacing between rows depends on the machinery used and on the way of training a plantation (min. 1.8 m – usually in home gardens, max. 3.5–4 m on commercial plantations). Raspberries are most often planted in rows and trained along a two-wire trellis which consists of poles 2 m high (10–12 cm wider), placed every 10 m at the most. Between the poles two galvanized wires are spread (3mm in diameter; the first one about 80 cm high, and the other 150 cm high) to make a trellis. A properly shaped seedling should have one cane, after trimming not shorter than 20–30 cm, and 5–7 mm thick, and from two to three roots approximately 10 cm long; it should be strong and free of diseases and pests.
Long cane frigo seedlings belong to a special type of raspberries which bear fruits on second year canes 1.7 m long, and develop many healthy buds which yield crop already in the first year. They come in pots or as bareroot plants, and are recommended especially for growing in glasshouses and tunnels. Recently, a revolutionary system of the long cane frigo seedlings planted in one row (seven seedlings per one linear metre) has been introduced. They are planted in raised beds, supported by a dripline irrigation system and covered with the gardening foil. Such a system provides plants ample light, thanks to which they bud abundantly along the whole length of canes. Raised beds also improve proper development of the root system.
In the first year after setting up a plantation, it is recommended to use non-chloride multi ingredient fertilizer containing nitrogen, phosphorus and potassium, and microelements (70 kg of N, 70 kg of P2O5, and 120 kg of K2O per 1 ha). When canes are 10 cm high, the soil is amended with nitrogen fertilization (ammonium or lime nitrate), usually at the dose of 40–50 kg/ha. Another dose of ammonium is added at the end of spring or at the beginning of summer at the dose of 50 kg/ha. In the following years, the grower decides about fertilizing based on the good look of plants and the quality of soil (following the laboratory analysis results). However, it is a common rule that the varieties bearing fruit on first year canes – due to their more vigorous growth – require increased fertilization than those which bear fruits on second year canes.
Weeding is one of the first treatments which are conducted both before setting up a plantation and during the vegetative season. It is important to remove not only weeds but also excessive amounts of suckers which compete for water and nutrients, and create favourable conditions for the development of cane diseases. A fallow herbicide treatment, mechanical cultivation of soil, turf (frequently mowed), soil bedding and raised beds can all be implemented in a raspberry plantation. The choice of the way of training a plantation depends on technical possibilities and local conditions of cultivation.
Pruning of floricane-fruiting (bearing fruit on second year canes) raspberries
On plantations set up in spring, plants are pruned right after planting and on plantations set up in autumn they are pruned in early spring. In both cases seedlings should be pruned low at the ground.
Pruning of raspberries trained along a single pole trellis
Training raspberries along a single pole trellis is good for a small garden in which there is not enough space for the two-wire trellis training system. After the fruit bearing period all fruiting canes should be pruned out and at most five young canes left to develop and bear fruits the following year.
Pruning of raspberries trained along the supported hedge-row (two-wire trellis) training system
After harvesting, the fruit bearing canes should be cut out and left only the healthiest first year canes, which should be gently tied to the first wire spread at about 1.0 m above the ground, and trimmed at the height of approximately 1.2 m. Only the strongest canes should be selected.
Pruning of primocane-fruiting (bearing fruit on first year canes) raspberries
Nurturing of these shrubs generally differs from pruning the varieties fruiting on second year canes. At the end of the vegetative season or in early spring all canes should be pruned out. According to the findings of the Horticulture Experimental Station in Brzezna, Poland, it is better to trim canes approximately 20 cm above the ground than just above the ground. Fewer canes develop in such cases, but they are stronger and bear bigger fruits. The varieties fruiting on first year canes are usually grown as free standing shrubs and that is why their pruning in the season is limited only to narrowing the row to 30–50 cm.
Raspberries belong to perishable and delicate fruits. They are harvested without the torus, when they come off the receptacle easily and have turned a deep colour, are soft and dry. They need to be quickly chilled down to +2°C or +5°C (two hours after harvesting at the latest).
CULTIVATION UNDER COVERS
Flat covers are usually used when growing raspberries fruiting on first year canes. In early spring, young canes are covered with white non woven fabric, loosely enough so that they could reach the height of approximately 30cm. Then, usually in mid May, the fabric is removed. This procedure accelerates their vegetation and the fruit bearing time. It was discovered that on plantations covered with non woven fabric the harvesting period was usually shorter.
Roof covers provide better microclimate for the plant development, pollination of flowers and bearing fruits. Such covers slightly accelerate the harvesting time but they greatly affect the crop. Additionally, they provide continuous harvesting even during adverse weather conditions.
Crops earlier than usual can be obtained when raspberries are grown under plastic tunnels and in glasshouses; however, it is the most expensive cultivation method.
DISEASES AND PESTS
In the Polish climatic conditions raspberries suffer from viral diseases, cane withering and fruit rotting which result in a potentially less profitable fruit crop. The following pests: raspberry blossom weevils, raspberry beetles, aphids, gall midgets, red spider mites and nematodes are most dangerous to raspberries. One should take care of the general health of the plantation at its very beginning by purchasing a healthy nursery material, and during the season all recommendations of the plant protection programme should be followed and observed.
Raspberries are not only tasty but also highly regarded for their nutritional values. They are thought to be a natural remedy for colds and tonsillitis, and have common diaphoretic (sweat-inducing) properties. They positively affect the nervous system and due to their content of iron they are recommended to persons suffering from anaemia. Moreover, raspberries contain precious dietary fibre which suppresses the development of rectal cancer. Their therapeutic properties result from their content of biologically active agents, especially of vitamin C, antocyans and ellagic acid. The latter most of all possesses strong antioxidant qualities, which has been proved by many research works. It suppresses the activity of mutagene compounds which are responsible for triggering off cancerous changes. Moreover, ellagic acid demonstrates antibacterial and antiviral characteristics. Not only do raspberry fruits boast therapeutic properties, but also their leaves contain tannins, organic acids, mineral salts, mucilage and a considerable amount of vitamin C, which is beneficial for a healthy development of the human body. An infusion of raspberry leaves possesses astringent, anti-inflammatory and antibacterial properties and it can also be used as an antidiarrheal agent, supporting in treating gastritis. It also relieves painful cramps of smooth muscles in the intestines, uterus and in the walls of vascular vessels. In ancient Tibetan medicine, raspberry leaves were reputed to be effective in treating neuroses, especially neurasthenia, and in severe and chronic infections. Raspberries should not be eaten by persons suffering from gout and renal insufficiency since they contain a considerable amount of purins.
J. Danek, Uprawa maliny i jeżyny, 2014
Jagodnik, March/April 2013