How to Grow Blackcurrants Successfully
Blackcurrants have one big disadvantage and a few smaller ones for me; but in spite of this, they are among my most prized soft fruits. I must explain the contradiction. My main concern is that, in most seasons, most modern varieties are barely sweet enough to be eaten fresh without added sugar. Lesser problems are that most varieties make big, wide-spreading bushes and that, sooner or later, reversion disease will begin to decrease their yield. But against this can be set the facts that they make better fain and freeze better than any other soft fruit, they are relatively free from most other pest and disease problems and they are both easy to grow and prune.
HISTORY AND TYPES OF BLACKCURRANT
Compared with red and white currants, the garden blackcurrant is botanically simpler in that, at least until very recently, it was derived from a single wild species. The wild blackcurrant, Ribes nigrum, occurs throughout much of central and eastern Europe and central Asia. In Britain, it’s probably not a native plant but exists wild as an escape from cultivation. Like many other soft fruits, it was probably collected and eaten from the wild long before it was cultivated, and the blackcurrant wasn’t described as a garden plant until medieval times when it was used for the flavouring and colouring of otherwise rather bland wine.
It wasn’t really until the eighteenth century that blackcurrants began to be used as a dessert fruit and even then many gardening writers shared my concern with its lack of sweetness. Subsequently, a large number of garden selections and crosses were made and, in recent years, other wild species have been used in breeding programmes to increase fruit size, pest, disease and frost-resistance and strig strength (the fruit stalk of currants is called a strig, although I have no idea why). Today, the blackcurrant remains much more popular in Europe than in North America, although its extremely high vitamin C content really ought to appeal to the health-conscious Americans.
Blackcurrants tolerate heavier, slightly wetter soils better than most other types of soft fruit and will thrive in gardens where others fail.
Heavy soils need less improvement to grow blackcurrants, although light, free-draining soils must have organic matter added. The ideal, however, is a deep, rich and moist loam, just on the acid side of neutral although it has always been my experience that they tolerate slightly alkaline conditions without detriment, and much better than most soft fruit.
The most important consideration is that blackcurrants are early coming into blossom and are very prone to damage from spring frosts. They must, therefore, have a sheltered position and should certainly never be planted in a frost pocket. I should add that one of the virtues of the newer varieties is that they are being bred to blossom later while managing still to crop early. Blackcurrants are moderately shade-tolerant but in any conditions other than full sun, it will be almost impossible to obtain fruit sweet enough to eat fresh. Although not as susceptible as raspberries or even red currants to bird damage, the most reliable crops will still be obtained from a fruit cage.
Blackcurrant bushes are available at different ages and sizes but much the best establishment will almost always be obtained from two-year old bushes. You can recognise these as they will usually have between four and six shoots. Smaller, one year-old plants will have at least two branches but will take longer to establish and begin cropping. Larger, three-year old plants will almost invariably have suffered too great a check to growth to be very successful. Be sure to obtain stock that is certified virus-free from a reputable supplier. It is very important to plant blackcurrants before mid-winter if at all possible (especially if they are being planted bare-rooted) because growth starts early and the tender young shoots will otherwise be damaged. Prepare a planting hole in the usual manner: about twice the size of the root ball and with well rotted manure or compost and a handful of bone meal well forked in. I have found the bushes respond better and produce stronger roots with animal manures than with compost. Blackcurrants should be planted deeply because new shoot development takes place from the very base of the plant. Plant so that the soil just covers the basal fork where the lowest branches arise. This will be much deeper than anything you may be used to, but be assured that it is correct. Gently firm the soil around the plant, taking care to slope it slightly away from the bush. After planting, cut back all the shoots to a point just above two buds from the base.
The large size of can be a drawback and because of this they should be planted 1.5-1.8m (5-6ft) apart, depending on vigour, with the significant exception of the variety ‘Ben Sarek’ which is best at about 1.5m (5ft) but can be grown perfectly satisfactorily at a distance of 1.2m (4ft). I must say, however, that these spacings are not solely intended to obtain good growth, for the plants will crop quite reasonably at closer distances if they are well fed; but you will never be able to find room between them to pick the fruit.
SUPPORTS AND TRAINING
Uniquely among the commoner soft fruit, blackcurrants aren’t amenable to being grown and trained in any way other than their natural bush form, for which they require no support at all.
PRUNING AND AFTERCARE
At the end of the first season, the number of branches on your plant should have at least doubled. Cut back one or two of the branches (depending on how many have been produced) to just above the base, as before, and also trim off to the base any additional weak and spindly shoots. Thethereafter is based on the fact that the best fruit will be produced on one-year-old wood with good crops also on two-and three-year-old wood but little of value on anything older.
Each year, therefore, cut back between one-quarter and one-third of all shoots to just above the base, always ensuring that the oldest shoots and any emerging at a shallow angle are cut off first — they will hang down with the weight of fruit and simply drag on the soil. Also, cut off any spindly or damaged shoots. The pruning can be done any time between the fruit reaching maturity and mid-winter but many gardeners find it useful to prune when the ripe fruit are still on the plant; the crop can then be picked from the detached branches.
FEEDING AND WATERING
Blackcurrants can be fed in the same way as most other soft fruit: apply 34g per square metre (1oz per square yard) of potassium sulphate shortly after mid-winter and then 70g per square metre (2oz per square yard) of Growmore or, blood and bone about two months later. The bushes should be well mulched directly after the second feeding and then watered if the weather is dry at the time when the fruit are beginning to swell. It shouldn’t be necessary to give sequestered iron unless the soil is very alkaline and old theories regarding the need to give extra large quantities of nitrogen to blackcurrants have been proved to be erroneous.
Although blackcurrants have a fairly extensive root system, damage can be caused to the young shoot buds by hoeing too close to the plant base. A wide band of mulch around the bush should keep down annual weeds in this area, and perennial weeds can, if necessary, be controlled with glyphosate.
Modern blackcurrant varieties generally are high yielding and so few plants will be needed unless you want to have fresh fruit over a long period, when a succession of early, mid-season and late varieties is called for. Most varieties should yield at least 4.5kg (10 lb) of fruit per season and unless they become affected with reversion disease, should continue to do so for 10 years or more.
HARVESTING AND STORING
Blackcurrants can be picked sequentially as they ripen, but this is a fiddly task and it is much better (especially if they are to be frozen or used for jam) to wait until all of the fruit on each bush is ripe. They will usually hang on the bushes for some time without dropping but to make the most of this, they really need to be in a fruit cage to prevent them being taken by birds. Although the individual fruit can be stripped as you pick them, some will inevitably be squashed and it is much better to pick the whole strig and strip them later.
Commercially, blackcurrants are harvested by machines that simply shake the bushes, and if bruising damage to the fruit is of no importance, then harvesting by manual shaking can be done in gardens, using either newspaper or old sheets beneath the bushes to catch the fruit. The compact and very heavy-cropping variety, ‘Ben Sarek’, responds particularly well to this method of harvesting. Blackcurrants will keep fresh for about seven days in a refrigerator but also bottle and freeze very well.
Reversion disease, the presence of which is betrayed by the symptoms of big bud, is easily the most serious of problems likely to affect your plants, althoughcan be troublesome on older varieties and in damp situations or where the plants are too close together.
Amos Black, very late. Large, delicious. Compact-growing bush.
Baldwin (Hill Top Strain), late. Thick-skinned, moderate size. High Vitamin C content. Moderately vigorous.
Blacksmith, mid-season. Heavy cropper, especially on light soil, good quality.
Boskoop Giant, very early. Sweet, tender skin.
Daniel’s September, very late. Large, heavy cropper. Surfers from yellowing of leaves.
Malvern Cross, late. Moderately large. Compact trusses. This variety is a vigorous, upright grower, and a good cropper.
Mendip Cross, early. Large. Long trusses. Slightly spreading bush. Very heavy cropper.
Wellington XXX, mid-season. Heavy, good quality. Strong grower, sulphur shy.
Westwick Choice, late. Sweet. Medium trusses. Vigorous.