Courgettes are generally easy to grow. They are quick, crop heavily, as long as you pick them regularly, and can even be grown in patio pots.
But things can go wrong. Because plants can die and the fruit fail to form properly it is difficult to know how many plants to grow. As a rule I would say grow one per person you want to feed, if you are happy to have courgettes twice or three times a week, while they are cropping. But if plants fail, you may want to plant more.
There are ways to avoid some problems and these are largely to do with varieties. Cucumber mosaic virus can ruin plants but there are resistant varieties such as ‘Defender’. Sometimes plants do not produce male and female flowers at the same time and if you only grow one or two plants the female flowers may not be pollinated, meaning the fruits will not grow. Some, such as ‘Partenon’ are parthenocapric, meaning the fruits will grow even if not pollinated. Buying just plain ‘courgette’ seeds is not a good move. You get loads of seeds, far more than you need. Buying a better variety, with specific qualities, is much better and though the seeds are far more expensive, and you only get six or so seeds per pack, who needs a pack with forty seeds in?
Cucumber mosaic virus is spread by aphids and infected plants produce small leaves which are distorted and usually yellow. The fruits will become distorted too. There is no cure and the plants have to be pulled up to prevent it spreading to other plants.
Mildew is also common. It is most prevalent in hot weather and when the soil is dry. A white, powdery coating covers the older leaves. There is no cure and you can cut off the older leaves. Try to keep the plants well fed and watered. In theory you can spray with a fungicide which will control the mildew on new foliage but I cannot recommend it. This plant is growing in a raised bed filled with a recycled compost which is low in nutrients and drains too freely. It was an experiment and it has told me what I needed to know about the compost.
Mildew should not be confused with the silvery patches that are entirely natural on some varieties.
Fruit rotting from the blossom end can be caused by a number of factors. It will happen if the flowers were not pollinated. If they are picked on the day the flower opens, or a day or two after they can be used but if they are left they start to rot. They should be cut off. This type of damage is also common late in the season or in wet weather when the flower rots and the rot spreads into the fruit. All good reasons to eat the courgettes when they are small.