Why Are My Blueberries So Small?

Berry size in blueberries is set by two things: the number of seeds inside the berry, which is determined by pollination quality, and the supply of water and nutrients during the six to eight weeks of fruit development. Berries with poor pollination contain fewer seeds and do not enlarge as much. Berries that run short of water at a critical moment stay small and can taste sharp rather than sweet. Both problems are very fixable once you know which one is causing the issue.

Pollination: the most overlooked factor

Blueberries are technically self-fertile but they produce significantly larger berries and higher yields when cross-pollinated by a different variety. This is because cross-pollination results in more seeds per berry, and seeds produce hormones that drive cell expansion — more seeds mean bigger fruit. If you have a single variety, planting a compatible second variety within about fifteen metres will noticeably improve berry size within one season. Varieties should ideally flower at overlapping times. Bumblebees are the primary pollinators of blueberries — their buzz pollination technique shakes pollen loose in a way honeybees cannot replicate — so anything you can do to attract and support bumblebees in your garden pays dividends at harvest time.

Drought stress during fruit development

The six to eight weeks between petal fall and harvest are when the berries need the most consistent water supply. Any drought stress during this period checks berry expansion and can set their final size permanently — cells that do not expand while dividing do not enlarge later. Keep the soil consistently moist but not waterlogged throughout June and July in temperate climates. Mulching with ten centimetres of pine bark or wood chip is essential in summer to hold soil moisture and moderate soil temperature. Container-grown blueberries are especially vulnerable and may need daily watering in hot weather.

Over-cropping and plant energy

A young or weakened bush that sets a very heavy crop will distribute its energy across too many berries, and none of them will reach full size. In the first two years after planting, remove all or most of the flowers so the plant builds a strong root and cane structure. On older plants, very heavy cropping years are often followed by smaller berries — the plant has simply stretched its resources. Consistent feeding with an acid-formulated fertiliser in spring and a potassium-rich feed as berries develop helps the plant support a full crop.

Variety characteristics

Some varieties genuinely produce smaller berries than others regardless of conditions. Wild-type or heritage varieties often produce smaller but more flavoursome fruit than modern cultivars bred for commercial size. If the berries have always been small since the plant was established and the growing conditions are good, this may simply be a characteristic of the variety. Newer cultivars like Bluecrop, Duke, Brigitta and Draper have been selected specifically for large berry size and are worth considering if consistent size is a priority.