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Poor pollination

Squash, cucumbers, strawberries and many fruit need insects to carry pollen; sweetcorn needs wind. Too few visits, cold, wet or very hot weather, or a single isolated plant, leave flowers unfertilised and fruit poorly filled.

Pollination & fruiting
A courgette with a withered flower and a shrivelling fruit
A courgette with a withered flower and a shrivelling fruit

What it looks like

The flower opens, then the fruit behind it fails.

  • Tiny courgettes and squash turn yellow and rot at the tip.
    Shrivelling baby fruit Tiny courgettes and squash turn yellow and rot at the tip.
  • Cucumbers and squash narrow or curl at the flower end.
    Pinched fruit Cucumbers and squash narrow or curl at the flower end.
  • Sweetcorn cobs with missing kernels, especially at the tip.
    Gappy cobs Sweetcorn cobs with missing kernels, especially at the tip.
  • Strawberries with seedy, undeveloped patches.
    Lumpy berries Strawberries with seedy, undeveloped patches.

How to confirm it

Check the flowers and the weather.

  1. Male and female flowers

    Squash flowers with a tiny fruit behind them are female; they need pollen from male flowers open at the same time.

  2. Bee visits

    Watch for bees on a warm morning; few visits in cold, wet weeks explains poor set.

  3. Planting layout

    Sweetcorn in a single row pollinates poorly; blocks work far better.

What to do

Do the bees' job for a week or two.

  1. Hand pollinate squash

    Pick a male flower, remove its petals and dab the pollen onto the centre of an open female flower, early in the morning.

  2. Tap corn tassels

    When silks appear, tap the tassels on a still morning so pollen falls onto them.

  3. Open the greenhouse

    Let insects in, or brush strawberry and tomato flowers with a soft brush.

  4. Remove failed fruit

    Pick shrivelled fruitlets so they do not rot.

Prevent it next time

  • Grow sweetcorn in blocks at least four plants square.
  • Plant flowers for pollinators near crops: borage, calendula, phacelia.
  • Choose self-fertile or all-female (parthenocarpic) cucumber varieties under glass.
  • Avoid insecticides when crops are in flower.

What not to do

Do not remove all the male flowers from squash; only greenhouse all-female cucumbers are better without them.

In the growing guides

Where the guides mention it, with plant-specific advice.

Sources

  1. Cucumber, pumpkin, squash: pollination failure, Washington State University Extension
  2. Pollination problems of vegetables, University of Maryland Extension