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Blackcurrants want more nitrogen than any other soft fruit in the garden. The chain is direct: nitrogen makes long strong basal shoots this summer, those shoots carry the heavy strigs next summer, and you cut out the old wood to make room for them. A bush that makes only short weak shoots is telling you it is underfed long before the crop shows it.
Apply a nitrogen-rich general fertilizer over the root area in early spring, just as the buds begin to move, and follow it with a thick mulch of well-rotted manure or compost. Potash matters too, because it fills the berries and hardens the wood, but on most garden soils nitrogen is the limiting factor and manure supplies both. Do not feed with nitrogen after midsummer: late soft growth does not ripen before the cold and it gets caught by frost and mildew.
| Timing | What to apply | Rate per bush | Purpose |
|---|---|---|---|
| Late dormant season, buds just moving | Nitrogen-rich general fertilizer | About 3 oz (85 g) spread over the root area | Drives the basal shoots that carry next year's fruit |
| Immediately after that | Well-rotted manure or garden compost | A full bucket, 3 in (8 cm) deep | Feeds slowly, holds water, suppresses weeds |
| Same time, on light or sandy soil | Sulfate of potash | About 1 oz (30 g) | Berry size and wood ripening |
| Once fruit has set | Water, not feed | See the watering section | Swelling the berries already on the strig |
| After harvest | Nothing nitrogen-based | None | Late soft growth is frost and mildew fodder |
Yellow leaves with green veins on the youngest growth usually mean the soil is too alkaline for the bush to take up iron and manganese, not that it needs more feed. On chalky ground use an acidifying feed and a deep organic mulch rather than more general fertilizer.
Water at the two moments that count
Blackcurrant roots are shallow and spread not much beyond the width of the bush, which makes them quick to feel a dry spell. There are two periods where dryness costs you directly. The first is from fruit set to the start of coloring, when a check makes the berries small and drops some of them off the strig. The second is midsummer, when the new basal shoots are extending; a drought then shortens next year's fruiting wood.
In a dry spell give each established bush 2 to 3 gallons (10 to 15 liters) once a week, applied slowly enough to soak in rather than run off the mulch. That is worth far more than a daily sprinkle, which wets only the top inch and encourages roots to stay at the surface where they dry out fastest.
There is one important exception. Stop heavy watering once the berries are close to fully colored. Water pushed into ripening fruit swells it faster than the skin can grow and the berries split, especially after a dry period followed by a downpour. Even watering through the season is the real defense against splitting.
| Stage | Water need | What happens if it goes dry |
|---|---|---|
| Bud burst to flowering | Moderate; rain usually enough | Weak flower trusses, poor set |
| Fruit set to first color | High; water weekly in dry weather | Small berries and bare gaps along the strig |
| Berries coloring up | Steady, not heavy | Sudden watering after drought splits the skins |
| Midsummer, after harvest | High; new shoots are extending | Short basal shoots means a poor crop next year |
| Late summer to leaf fall | Low; let it slow down naturally | Watering now makes soft wood that will not ripen |
Mulch, and never dig around a blackcurrant
The feeding roots run in the top few inches of soil and out through the mulch itself. Forking or hoeing around the stool tears them, and the bush sulks for weeks. Mulch is how you deal with weeds instead: a 3 inch (8 cm) layer of compost, rotted manure or bark laid over clean ground in spring smothers annual weeds, holds moisture through the dry weeks and feeds as it breaks down.
Keep the mulch just clear of the stems themselves so the crown does not sit permanently wet. Pull by hand any perennial weed that comes through, taking the root with it. Grass growing right up to the stool is worse than it looks: it competes directly for the nitrogen and water the bush wants most.
- Weed thoroughly before you mulch Hand-pull everything inside a circle at least 3 feet (90 cm) across, getting perennial roots out whole. Mulch laid over living perennial weed simply gives it better growing conditions.
- Water the ground first Mulch holds in whatever moisture is underneath it. Laying it over dry soil locks the dryness in. Soak the root area first if there has been no recent rain.
- Lay it thick and wide Three inches (8 cm) deep, covering the ground out to at least the spread of the branches, since that is roughly where the roots end. Thin mulch does not suppress weeds and dries out in days.
- Keep it off the stems Leave an inch (2 to 3 cm) of clear soil around each stem. Mulch packed against the crown keeps it wet, and wet crowns rot.
- Top it up every spring The layer disappears into the soil over a season, which is exactly what you want. Renew it each spring after feeding, and clear out any old leaves that collected inside the stool over winter.
Supporting, netting and general upkeep
A well-fed bush loaded with fruit splays outwards until the lowest strigs rest on the soil, where they get splashed with mud and eaten by slugs. A ring of stakes and string around the outside of the stool at about 2 feet (60 cm) high, put in before the fruit sizes up, holds the stems up and costs nothing. It also makes picking far quicker.
Birds strip a ripening blackcurrant bush faster than any other soft fruit, sometimes taking a full crop in two days. Net before the first berry starts to color, not after you notice damage, and keep the net well clear of the outer stems so birds cannot reach through it. Check daily that nothing is caught inside it.
The rest of the summer work is watching rather than doing: look at the shoot tips for the white bloom of mildew, at the leaves for aphid distortion, and at the buds through the winter for the round swelling of gall mite. All three are much cheaper to deal with early.
Keep a short log through the season: the date the buds burst, the date the first flowers opened, when you fed and mulched, every watering in a dry spell, and the date you netted. After two years those dates tell you exactly how early to have the net ready and whether your bushes are drying out at the stage that costs you the most.