Why Do My Strawberry Flowers Fall Off Without Setting Fruit?

Strawberry flowers that open, look perfect, and then drop without developing into fruit — or develop into tiny, hard, green knobs that shrivel rather than growing into full berries — have a pollination failure. Strawberry fruit development requires effective pollination of the receptacle's many tiny achenes (the seeds), and when pollination is incomplete or entirely absent, the receptacle does not develop into a proper berry. Understanding the conditions that prevent pollination helps you address the problem directly.

Cold temperatures during flowering

Strawberry flowers are damaged by frost. The central receptacle of the flower turns black in the centre (the classic "black eye" symptom) when the pistils are killed by freezing temperatures — and a flower with killed pistils cannot set fruit. Late spring frosts are a common cause of fruit failure in early June-bearing varieties. If your strawberry flowers have dark, blackened centres after a cold night, frost is the cause. Covering plants with fleece on nights when frost is forecast during flowering prevents this.

Low pollinator activity

Strawberry flowers are insect-pollinated, primarily by bees. In cold, wet, or windy weather, bees and other pollinators are less active and fewer flowers receive adequate pollen. A week of cold, grey weather during peak flowering can result in poor fruit set across the whole bed. If your plants are under a polytunnel or cloche, pollinators may not be able to access the flowers — remove covers during the day to allow bee access during the flowering period. For plants under glass, hand-pollinate by brushing across flowers with a soft paintbrush.

Growing under cover without ventilation

Strawberry plants forced under glass or polytunnel in early spring for an early crop will not set fruit unless pollinators can enter, or unless hand-pollination is carried out regularly. Open vents and doors during the day throughout the flowering period to allow bees in. If the structure does not allow this, hand-pollinate every two to three days during flowering.

Virus-infected plants with poor vigour

Plants infected with strawberry viruses (often symptomless or producing only mild stunting) can produce flowers that fail to set. If poor fruit set is persistent year after year on the same plants despite good weather conditions, the plants may be virus-affected. Replace with certified virus-free runners from a reputable supplier and plant in a fresh site.