Poor pollination

also called Incomplete pollination, Poor fruit set

Courgettes that swell an inch and then rot at the tip, corn cobs with gaps, misshapen strawberries. Not enough pollen reached enough of the flower.

Disorder Serious Doesn't spread

What you'll see

Young cucurbit fruit growing to a few centimeters, turning yellow at the blossom end and rotting off.
Sweetcorn cobs with scattered missing kernels, or a whole bare tip.
Strawberries and apples lopsided or with a flat side where the seeds did not set.
A plant covered in flowers with almost no fruit behind them.
Cucumbers curved and pinched at one end rather than straight.

Why it happens

A cucurbit carries separate male and female flowers, and each female must receive several visits to fill out. Sweetcorn is wind-pollinated and needs a block of plants rather than a row for the pollen to fall where it is wanted. Anything that keeps the bees away or interferes with pollen — cold, wind, heavy rain, a heatwave, an insecticide sprayed at midday — leaves the fruit half-made. The first flush of male-only flowers on a young squash is normal and not a problem.

Cold, wet or windy weather during flowering; very hot weather, which sterilizes pollen; few pollinators in the garden; sweetcorn grown in a single long row; and single fruit trees with no compatible partner nearby.

Treating it

Hand-pollinate. Pick a male squash flower, strip the petals, and dab the pollen onto the center of each female flower in the early morning — it works every time and takes a minute.
Tap or shake sweetcorn tassels over the silks on a still morning to shed the pollen where it is needed.
Remove the aborted fruitlets so the plant puts its energy into the next flowers.
Never spray insecticide on open flowers, and never during the day when bees are working.
Give it a week; a young courgette plant that is dropping fruit is often simply not yet producing enough female flowers.

Keeping it away

Grow sweetcorn in a block at least four rows deep, never in a single line.
Plant open, nectar-rich flowers — borage, phacelia, calendula, alyssum — through the vegetable garden for the bees.
Check that fruit trees have a compatible pollination partner in flower at the same time.
Shelter the garden from strong wind, which keeps bees grounded.
Avoid all insecticide use during flowering, including the organic ones.

Who gets it

Courgettes, squash, pumpkins, cucumbers and melons; sweetcorn; strawberries; apples, pears and plums.