Blackcurrant

Light and exposure

The blackcurrant does not need full sun to produce well, and that is good news for gardens that only get partial sun. It tolerates partial shade very well, which lets you give it a cool corner of the garden, to the east or at the foot of a wall that does not bake in the afternoon. Too scorching a position displeases it because it dries out the soil that it needs cool.

In practice, aim for a bright spot but protected from drying winds and blazing sun. A place that gets morning sun and a little shade in the afternoon suits it wonderfully, and gives well scented berries without the plant suffering from summer drought.

Watering

The watchword is coolness. The blackcurrant has fairly shallow roots and suffers quickly when the soil dries out, above all at the time the berries form and swell, between late spring and midsummer. A lack of water at this period makes the fruit drop or leaves it small and sour.

Water copiously during dry spells, aiming at the base and not the foliage. A good organic mulch in spring, dead leaves, dried grass clippings or coarse compost, keeps the moisture in and avoids watering too often. On heavy cool soil, summer watering will only be needed during real heatwaves.

Soil and repotting

The blackcurrant likes a cool, rich and deep soil, rather heavy, that holds water well. Clay soils, often shunned by other fruit shrubs, suit it perfectly as long as they are not permanently waterlogged. A good input of compost or well rotted manure at planting gets it off to a good start.

It likes slightly acidic to neutral soils and dreads active lime, which causes a yellowing of the leaves. If your soil is poor, enrich it each winter with mature compost on the surface. A living soil covered with a mulch reproduces fairly well the cool woodland edges the shrub comes from.

Temperature and humidity

This is a plant of the North, built for hard winters. The blackcurrant is perfectly hardy and withstands frosts of minus 20 degrees without flinching, and down to minus 30 degrees on well ripened wood. It even needs a good spell of winter cold to flower and fruit properly the following year: count on 800 to 1500 hours below 7 degrees depending on the variety.

The sensitive point is in spring. The early flowering, from the first mild spells, can be hit by a late frost that scorches the flowers and compromises the harvest. Choose by preference a variety that flowers a little later, and avoid hollows where cold air stagnates on clear nights of late spring.

Pruning and upkeep

This is the key task, and it rests on a simple rule: unlike the redcurrant, the blackcurrant fruits mainly on one year old wood, that is the young shoots of the previous year. The old wood, for its part, exhausts itself and produces less and less. All the pruning therefore aims to renew the framework constantly to encourage the emission of productive young wood.

In winter, when the shrub is at rest, remove at the base the oldest branches, those over three years, recognisable by their dark cracked bark. Keep the young vigorous shoots, which are lighter, and remove the dead or spindly wood. On an adult plant, you thus take out about a third of the old branches each year to force new shoots from the stump. A well renewed clump stays productive for ten to fifteen years.

Pests and diseases

The most dreaded enemy of the blackcurrant is reversion, a serious viral disease spread by the bud mite (Cecidophyopsis ribis). It shows in the large round swollen buds in winter, in deformed leaves and in a gradual drop in production. There is no treatment: pull up and burn the affected plants without waiting so as not to contaminate the neighbours.

Watch also for American powdery mildew, which covers leaves and young shoots with a white felting in mild humid weather, and blister rust, whose cycle passes through five needle pines: avoid planting the blackcurrant too close to these conifers. Airing the clump by pruning and gathering the diseased leaves greatly limits these two fungi in a damp climate.

Propagation

The blackcurrant propagates very easily from hardwood cuttings, an almost foolproof method within everyone’s reach. In autumn, after leaf fall, take from a healthy plant well ripened shoots of the current year, and cut them into sections of twenty to twenty five centimetres bearing several buds.

Plant these cuttings three quarters deep in loose cool soil, leaving only two or three buds showing. Leave them in place all winter and spring: the moisture of the cold season does the work, and rooting happens on its own. By the following autumn, you will have young plants ready to set in their final place.

Month-by-month care calendar

Green Hub tips

• Remember the rule that makes all the difference: the blackcurrant fruits on one year old wood. In winter, cut the old wood over three years to force young productive shoots.
• A large round swollen bud in winter is not a good sign but that of reversion. Pull up and burn the affected plant without hesitation to protect the others.
• Do not plant your blackcurrant near a five needle pine: this conifer hosts the blister rust that then comes to spot the foliage.
• Propagate for free in autumn: a simple stem of the current year’s wood planted three quarters deep in cool soil roots on its own over winter.
• Keep the base cool with a good mulch: shallow roots left dry while the clusters are filling give small sour berries.