Why blackcurrants need a regular overhaul

Blackcurrants are generous plants. Give them a decent spot and they will crop heavily for years with very little fuss. Left entirely alone, though, a bush turns into a dense thicket of dark, ageing stems that produce less fruit each season — and hide what it does produce where you cannot comfortably reach it.

The reason is simple. Blackcurrants carry the bulk of their crop on one-year-old wood, the strong shoots that grew during the previous summer. A stem's first year or two of life is its most productive. By the time it is three years old it is still alive and leafy, but its cropping days are largely behind it, and it is shading the ground and taking up space a vigorous young shoot could use far better.

So pruning a blackcurrant is not really about cutting the bush back. It is about renewal — taking out older wood steadily so there is always plenty of young growth coming through to carry next summer's fruit.

The best time to prune

There are two good windows, and either will do.

The first is straight after picking, usually late July into August. This is my favourite moment, because you can see exactly which stems cropped well and which were a waste of space, and the bushes have the rest of the growing season to push out new shoots before the cold arrives.

The second is winter, from November to February, while the bush is dormant and bare. The structure is far easier to read without leaves in the way, which is a real help with an overgrown plant. The one rule to hold on to is that you are only ever removing the old, dark, thick stems. Cut into the young pale wood in winter and you are cutting away next year's crop.

Avoid spring pruning once growth has started. The sap is rising, the wounds bleed, and the bush wastes energy repairing itself just when it should be flowering.

Which wood to cut and which to keep

Age is easy to read once you know what you are looking at. Old stems are thicker, darker brown or grey, often with slightly peeling bark. New shoots are pale, slim, flexible and smooth — they were this season's growth, and they are what you are protecting.

Work through the bush with sharp, clean secateurs and:

• Cut out every stem that is three years old or older, taking it right down to ground level.
• Remove any dead, damaged or diseased stems, and anything broken or nibbled.
• Take out thin, spindly shoots from the middle of the bush, where they will never crop properly.
• Leave the strongest young shoots, ideally spaced 30–60cm apart around the base, with room to grow.

As a rough target, aim to finish with eight to twelve main stems per bush, in a mix of ages: roughly a third one-year-old, a third two-year-old and a third three-year-old. Cut cleanly, at a slight angle, leaving a stub no more than a couple of centimetres long. Ragged stumps rot, and rot travels.

Removing low branches for airflow and easy picking

Once the old wood is out, look at the shape from the side. Blackcurrants have a habit of throwing out branches that droop towards the soil, and these cause more trouble than they are worth.

Fruit hanging near the ground gets splashed with soil, which invites grey mould and slug damage, and it ripens unevenly in the shade. Low growth also traps still, damp air at the base of the bush — exactly the conditions powdery mildew and botrytis like best. Cutting these branches away lifts the canopy, lets air move through, and makes the whole bush far quicker to pick.

Aim for a slightly open, goblet-like shape: clear space at the base, stems fanning outwards and upwards. If you can crouch beside a bush and see daylight through it, you have got it about right.

Renovating an old, neglected bush

If you have inherited an allotment or garden with a blackcurrant that has not been touched in a decade, do not panic and do not reach for the spade.

For a badly congested bush, cut a third of the oldest stems to the ground each winter for three years. It sounds slow, but you keep some cropping going throughout, and by the end you have a completely rebuilt plant. If the bush is truly beyond help, cut everything down to ground level in one winter. You will lose the following summer's crop almost entirely, but the bush will throw up strong new shoots and be back in production the year after.

Aftercare to set up next summer's crop

Pruning is half the job; feeding and mulching does the rest.

In early spring, spread a generous mulch of well-rotted manure or garden compost around the base of the bush, keeping it clear of the stems themselves. Add a handful of general-purpose fertiliser, and if you want to push fruit rather than leaf, lean towards sulphate of potash rather than anything high in nitrogen.

Water well during dry spells while the bushes are flowering and swelling their fruit — blackcurrants have shallow roots and resent drying out. And if birds strip your crop most years, net the bushes as the berries begin to colour.

Finally, remember what the pruning was for. Every strong new shoot growing away this summer is already carrying next year's blackcurrants. Look after it, and the crop will look after itself.