How to Grow Blackcurrants: 6 Steps - wikiHow:
Harvest. Don't pick the blackcurrants too soon. Once ripened, leave the berries to hang on the bush a few extra days to improve the flavour. When you see some of the upper level berries fall off unaided, the blackcurrants are ready for harvesting.
Prune. Each bush should carry around 6 to 10 shoots. Remove the oldest canes post-harvest yearly. This will stimulate the new growth.
Pruning off the oldest canes will renew the entire bush about every three years.
Blackcurrants are quite different in their requirements to red or white ones. They must have sunshine and very rich soil, with a thick mulch added every year. Their pruning regime is different, too, as instead of producing fruit on spurs they form on 'strigs' (bunches of fruit). To get the best from them, you should remove a third of all stems every year so that the bush completely replaces itself every three to four years. Another
way is to have three bushes and to remove all the growth from one of them each year.
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