Why do my blueberries hardly crop?

Blueberries are unforgiving about two things and easy about everything else. They need a soil pH of roughly 4.5 to 5.5, which is more acidic than almost any UK garden soil, and they are shallow-rooted enough to be badly set back by drying out. Beyond that they are hardy, need little pruning for their first few years and live for decades — provided the two requirements are actually met rather than approximately met.

Step by step

1. Check the growing medium first.Ericaceous compost in a pot, or genuinely acid ground below about pH 5.5. In neutral or alkaline soil the plant slowly starves regardless of feeding, and the leaves yellow with green veins.
2. Check the water.Hard tap water is alkaline and raises the compost pH every time it is used. In a hard water area a potted blueberry can go from healthy to chlorotic in one season. Rainwater from a butt is the fix.
3. Plant a second variety.Blueberries set far better with cross-pollination. Two or three different varieties with overlapping flowering give substantially more, larger fruit than one plant alone, even on so-called self-fertile types.
4. Never let them dry out.The roots are fine and shallow. A pot that dries once while the fruit is swelling will shed or shrivel it. Mulch the pot surface and check daily in warm weather.
5. Give them sun.They tolerate part shade but crop and sweeten far better with a good half-day or more of sun. Shaded plants flower less and taste watery.
6. Feed with an ericaceous fertiliser only.Ordinary fertilisers raise the pH and can contain lime. Use a feed formulated for ericaceous plants in spring and early summer, at label rate.
7. Be patient with young plants.A blueberry takes three to four years to build up to a proper crop and reaches full production at around six to eight years. A two-year-old plant with a handful of berries is normal.
8. Prune once the bush is established.Nothing much for the first three years beyond removing weak and damaged shoots. After that, annual renewal pruning keeps young productive wood coming.
9. Net for the fruiting period.Birds take ripening blueberries systematically. Net with fine mesh over a frame from the point the fruit begins to colour, and take it down at the end.
10. Top-dress and repot on a cycle.Fresh ericaceous compost as a top-dressing each spring, and repot into a bigger pot or refresh the compost every two or three years.

Tips

• In most of the UK the reliable way to grow blueberries is a large pot of ericaceous compost, not the open ground. Trying to acidify a whole bed rarely holds.
• Sulphur chips scattered on the compost surface annually counteract the slow pH drift, which is useful when rainwater runs out in a dry summer.
• A mulch of pine needles or composted bark is mildly acidic and helps hold moisture on a shallow-rooted plant.
• Autumn colour on a blueberry is spectacular and it is a genuinely ornamental shrub, which makes the pot easy to justify.
• Varieties differ in season: Duke and Spartan are early, Bluecrop and Berkeley mid, Chandler and Brigitta late. Two or three across the range gives cross-pollination and a long picking season at once.

Common mistakes

• Growing one plant alone — Cross-pollination makes a large difference to both the number and the size of berries, even on varieties sold as self-fertile.
• Watering with tap water in a hard water area — Each watering raises the compost pH slightly. Above about pH 6 the plant cannot take up iron, the leaves yellow between green veins, and cropping falls away.
• Planting into ordinary garden soil — The surrounding soil buffers the pH back up within a season or two and the plant declines. A large container of ericaceous compost works anywhere.
• Letting the pot dry out in summer — Shallow fine roots cannot recover quickly, and fruit shrivels or drops. Consistent moisture is as important as the pH.

If it doesn't work

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