Why do my flowers open and then drop off without setting fruit?

There is a specific and useful difference between buds that never open, flowers that open and drop, and small fruit that forms and then falls. Each has a different cause. A flower that opens fully and then drops leaving a bare stalk has told you the plant had the resources to flower and something went wrong at pollination.

Step by step

1. Confirm which stage is failing.Buds falling unopened is bud drop, a water and consistency problem. Open flowers dropping with a bare stalk behind them is pollination failure. Small fruits forming and then dropping when marble-sized is fruit drop, usually a natural thinning or a water problem.
2. Check whether pollinators can reach the flowers.Plants in a greenhouse, a conservatory, a porch or under fleece may never see an insect. Ventilate, open doors, remove covers once flowering begins, and plant open, nectar-rich flowers nearby to bring pollinators to the area.
3. Check the temperature at the time of flowering.Tomatoes and peppers set poorly above roughly 30°C and below about 13°C, because the pollen itself fails. Runner beans drop flowers in hot dry weather and in cold nights. Courgettes abort in cold, wet spells. Weather is the answer more often than anything you did.
4. Look at humidity if the plants are under glass.Very dry air makes tomato and pepper pollen fail to stick, and very humid air makes it clump. Damping down the floor in a hot greenhouse in the morning, and ventilating well, both improve set.
5. On courgettes, squash and cucumbers, check the flower sexes.Female flowers have a small immature fruit behind them; males have a plain stalk. Early in the season a plant often produces only males, or only females, and nothing sets until both are open together. This resolves itself as the plant matures and needs no intervention.
6. Hand-pollinate where it is worth it.For courgettes and squash, pick a male flower, strip the petals and push it into the centre of a female flower in the morning. For tomatoes under glass, tap or gently shake the flower trusses daily, or run a soft brush over them, to shed pollen.
7. Check for a pollination partner on fruit.Many apples, pears, plums and cherries need a compatible variety flowering at the same time. A tree that flowers profusely and never sets is very often alone or paired with something in the wrong pollination group.
8. Rule out watering swings.Irregular watering causes flower and fruit drop directly, especially in containers and grow bags. Steady moisture through flowering matters more than any feed.
9. Do not add nitrogen.A plant pushed with nitrogen makes leaves and drops flowers. If anything is needed once flowering begins, it is a high-potash feed, and only once the plant is genuinely in flower.

Tips

• Runner beans dropping flowers in a heatwave will start setting again as soon as the weather breaks. Watering the roots heavily helps; misting the flowers is an old piece of advice with little evidence behind it.
• Bumblebees are far better than honeybees at tomatoes, because they buzz-pollinate. A greenhouse with the door open in the morning usually gets them.
• Early courgettes rotting at the tip rather than dropping is a different problem — that is unpollinated fruit rotting, and hand-pollination fixes it.
• A first-year fruit tree that flowers and sets nothing is often simply too young. Let it establish rather than intervening.

Common mistakes

• Feeding a plant that is dropping flowers — The plant had enough to flower. Adding nitrogen shifts it back towards leaf and makes matters worse.
• Keeping the greenhouse closed to keep it warm — Above about 30°C tomato pollen fails, and a closed greenhouse in July is far hotter than that. Ventilation is part of the fruit set.
• Assuming a lone apple tree will manage — Most need a pollination partner in a compatible group. Neighbours' trees often provide it, but a tree in an isolated garden may genuinely have none.
• Growing under fleece or mesh through flowering — It excludes the pollinators along with the pests. Remove covers once flowers open, or lift them during the day.

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