Why are my courgettes rotting before they grow?

Why small fruit yellows and shrivels at the end — poor pollination in most cases — and how to hand pollinate in a wet or cold summer.

Difficulty: beginner
Time: 20 min
Read: 3 min

Short answer

Small courgettes that yellow, soften and rot at the flower end have not been pollinated. In cool wet weather bees do not fly and the female flower is not fertilised, so the fruit aborts. Hand pollinate with a male flower and it stops immediately.

Courgettes carry separate male and female flowers. The female has a miniature courgette behind the flower before it is even open; the male has a plain stalk. Both have to be open on the same morning and something has to move pollen between them.

Step by step

Check whether it is pollination or rot.A tiny fruit that yellows from the flower end and shrivels was never pollinated. A larger fruit going soft and fuzzy in wet weather is grey mould on the dead flower, which is different.
Learn to tell male from female flowers.The female has a small immature fruit between the flower and the stem. The male has a plain thin stalk. Plants often produce only male flowers for the first week or two, which is normal.
Hand pollinate in the morning.Pick a male flower, peel the petals back, and dab the pollen-bearing centre directly onto the centre of an open female flower. Do it before midday when the flowers are freshly open.
Do it daily in a poor summer.In a cool wet July, hand pollination every morning is what makes the difference between a crop and nothing. It takes seconds per plant.
Remove the dead flower from set fruit.In wet weather the spent flower sits on the end of the fruit and grows grey mould, which then rots the fruit. Pull it off once the fruit is clearly swelling.
Improve air movement around the plants.Courgettes planted too close hold damp air. Space them properly and remove some of the older lower leaves in a wet summer.
Water at the base, not over the plant.Wet flowers and wet crowns in cool weather encourage the mould that causes the second kind of rot.
Attract pollinators.Flowering plants nearby, and avoiding insecticide sprays anywhere near the plot, makes natural pollination far more reliable.
Feed once fruiting starts.A high-potash feed weekly once the first fruits set. A starved plant aborts fruit even when pollination is fine.
Pick regularly.Leaving a marrow-sized fruit on the plant slows or stops further fruit setting. Picking every couple of days keeps production going.

Tips

Female flowers have a tiny courgette behind them before they even open.
Only male flowers for the first fortnight is completely normal.
Hand pollination before midday, with a picked male flower, takes ten seconds and works.

Common mistakes

Assuming a disease and reaching for a spray — The overwhelming cause is failed pollination, which no spray addresses. Check the flowers before treating anything.
Leaving the dead flower attached to a developing fruit in wet weather — It goes mouldy and the mould spreads into the fruit tip. Pull the spent flower off once the fruit has clearly set.

If it doesn't work

Tiny fruit yellows and shrivels

Cause: Not pollinated — Fix: Hand pollinate each morning with a freshly opened male flower.

Grey fuzz on the flower end of a growing fruit

Cause: Botrytis on the dead flower — Fix: Remove the spent flower, improve airflow, water at the base.

Only male flowers

Cause: Normal early behaviour, or a young plant — Fix: Wait. Females follow within a week or two.

Plenty of flowers, few fruit, late season

Cause: Plant exhausted or fruit left on too long — Fix: Feed with high potash weekly and pick every couple of days.

Questions people ask

Why are my courgettes yellowing and falling off?

They were not pollinated. In cool or wet weather bees do not fly, the female flower is not fertilised, and the plant aborts the fruit. Hand pollination solves it.

How do I hand pollinate?

Pick a male flower in the morning, peel the petals off, and dab the pollen-bearing centre onto the middle of an open female flower. One male can pollinate several females.

Do I need two plants?

No — courgettes carry both male and female flowers on the same plant. Two plants does give more overlap of open flowers, which helps in a poor summer.