Blueberry Poor Pollination: Small or Few Berries Explained

A blueberry that flowers well but gives you a handful of small, slow-ripening berries is often short of pollen, not short of care. Blueberry flowers need compatible pollen moved onto them by bees while the flower is still receptive. On a balcony with one plant and few bees, that step often falls short.

The good news: the fix is usually a second plant and better access for bees, not a new fertilizer. Most of the research below comes from commercial fields and home gardens. We note where it applies differently to a pot.

What poor pollination looks like

Michigan State University Extension explains, in Invest in pollination for success with highbush blueberries, that northern highbush plants can set some berries with little or no bee visits. Those berries are small, slow to ripen, may drop early, and are mostly not worth picking.

Other clues from the same article:

• Fertilized ovules form the tiny seeds, and those seeds release hormones that make the berry grow. Poorly pollinated berries stay small.
• In well-pollinated plants, the flower petals drop while still bright white. Petals that turn brown and discoloured on the bush point to poor pollination.
• Flowers are receptive as soon as they open. Their chance of becoming a berry declines after three days, and they are unlikely to set fruit after five to six days.

Check your cultivar and blueberry type

How much a blueberry needs a partner depends on its type:

• Rabbiteye blueberries need another rabbiteye cultivar. Clemson HGIC says in its blueberry factsheet that rabbiteyes have a great degree of self-incompatibility, so at least two varieties are required. Oregon State says rabbiteyes do not produce fruit with self-pollination, apart from the partly self-fertile ‘Pink Lemonade’.
• Half-high cultivars, often sold for pots, do not produce much fruit with self-pollination, according to Oregon State’s home garden guide (EC 1304). Plant more than one half-high cultivar.
• Northern highbush cultivars vary. Michigan State lists ‘Duke’ as needing no pollinizer, ‘Bluecrop’ and ‘Legacy’ as benefiting from one, and ‘Spartan’, ‘Chippewa’ and ‘Polaris’ as needing one. Oregon State says cross-pollination improves berry size and quantity even in self-fruitful highbush types.
• Southern highbush and dwarf container cultivars are generally self-fertile, says Clemson, but give more and larger berries when cross-pollinated by another cultivar.

RHS sums up the garden view: most blueberries are partially self-fertile, but cross-pollinated plants produce larger harvests, so plant two or preferably three varieties if you have room.

How to improve pollination for potted blueberries

1. Add a second cultivar of the same type. University of Maryland Extension notes in its container blueberry guide that another variety in a separate container encourages cross-pollination as long as the two bloom at the same time.
2. Match bloom times, not harvest times. Oregon State notes that northern highbush cultivars ripen at different times but bloom at the same time. Clemson lists recommended partners for each rabbiteye and southern highbush cultivar.
3. Put the pots where bees can reach them. Move containers outdoors or to an open, sunny spot while they flower. A blueberry kept behind glass during bloom gets few or no bee visits.
4. Value bumble bees and native bees. Michigan State explains that blueberry pollen is held inside the flower until bees shake it loose. Bumble bees release it by vibration, called buzz pollination. One bumble bee visit can deposit enough pollen, where honey bees need about three. Alabama Cooperative Extension notes in its rabbiteye guide that carpenter bees, blueberry bees and some other solitary bees are effective pollinators.
5. Protect flowers from frost without shutting out bees. RHS advises moving potted plants under cover overnight or covering them with fleece if frost is forecast during flowering, then removing the cover by day so insects can pollinate.

We found no extension guidance giving a tested hand-pollination method for home blueberries. A second cultivar and access to bees are the steps the sources support.

Rule out other causes of small or few berries

• Frost at bloom. Oregon State notes that open blueberry flowers are susceptible to frost damage at −2 °C (28 °F). Damaged flowers set no fruit.
• Weather during bloom. Oregon State says rain or cool weather during bloom can reduce fruit set by limiting bee activity.
• Pruning. Oregon State notes that cultivar is the main factor in berry size, but poorly pruned bushes produce small berries. Short, twiggy laterals give small fruit.
• Young plants. Oregon State and University of Maryland both advise removing flowers in the first season so plants build roots. University of Maryland says a full crop takes about five years.
• Dry pots. Oregon State notes that adequate water is essential for good yields and fruit quality.

The blueberry hub collects our other blueberry pages.

Related guides

Other blueberry problems we cover: root bound, scorched leaves.

References

• Michigan State University Extension: Invest in pollination for success with highbush blueberries (hosted by Washington State University)
• Oregon State University Extension: Growing blueberries in your home garden (EC 1304)
• Clemson Cooperative Extension HGIC: Blueberry
• Alabama Cooperative Extension System: Home Gardening Rabbiteye Blueberries
• University of Maryland Extension: Growing Blueberries in Containers
• RHS: How to grow blueberries