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I have harvested some healthy fruits from my courgette plants, but now one of them has courgettes with ends which are yellow and shrunken. What causes this:
Pollination problem ????  Mineral deficiency ????  I've been watering the plants when it was dry.

Don't know if I can answer that Dandelion, but can confirm I've had a few yellow-ended ones too.   I've simply harvested them and chopped off the yellow ends, and they've been fine to cook.
I'm growing a mini bush variety, and some of the them have developed some "gourd-shaped" fruits - narrow necks and bulbous bases.
I wonder if in the case of these mini courgettes these problems are a weakness in the breeding/variety?

The variety I'm growing is 'all green bush'.

It is a simple pollination problem, courgettes are notorious for it as male and female flowers, which are needed for pollination, are triggered at different temps.

If caught early enough they are perfect to eat but fear not, give it a few days and they will be cropping like mad.

Jerry