Why are my cucumbers bitter, stunted or misshapen?

Cucumbers are less forgiving than courgettes. They want warmth, humidity and an absolutely steady water supply, and they signal any shortfall in the flavour and shape of the fruit. Two different sorts of cucumber also want opposite treatment on the male-flower question, which is where a lot of confusion comes from.

Step by step

1. Establish which type you are growing.All-female greenhouse varieties produce almost no male flowers and are meant to fruit without pollination — pollinated fruit on them goes bitter and swells oddly at the end. Outdoor ridge and many modern varieties need pollination and the males must be left.
2. Remove male flowers only on all-female greenhouse types.If the packet says all-female or gynoecious, pinch off any male flowers that do appear — the ones on a plain thin stem with nothing swollen behind. On any other type, this destroys the crop.
3. Water consistently and generously.Cucumbers are more than ninety per cent water and demand a lot of it. Any swing between dry and wet shows up as bitterness. In a greenhouse in summer that means daily, sometimes twice.
4. Keep the temperature steady.Cold nights below about 12°C and scorching days above about 30°C both stress the plant into bitterness. Ventilate hard in the day, close down before dusk, and do not put plants out too early.
5. Feed once fruiting starts.A high-potash tomato feed at every second watering. A hungry plant produces small, tapering, pale fruit that never fills out at the end.
6. Keep the air humid under glass.Damping down the greenhouse floor on hot days raises humidity, reduces stress and discourages red spider mite, which is the pest cucumbers suffer from most.
7. Pick young and pick often.Left on the plant, fruit goes bitter at the stem end, and a maturing cucumber slows the whole plant. Pick at the size the variety is meant to reach and go over the plant every two or three days.
8. Interpret shape.Fruit that swells at the flower end and tapers to nothing at the stem end usually means poor pollination or a plant short of water and feed. Curled fruit usually means it grew against a leaf, a stem or a wire — training the plant properly prevents it.
9. Train the plant on a support.A single stem up a string or cane, with side shoots stopped two leaves beyond a fruit, gives straight fruit, better airflow and easier picking than a sprawling plant.

Tips

• Never let a cucumber plant wilt. Unlike a courgette, it does not simply recover — the fruit on the plant at the time will be affected.
• Growing outdoor ridge cucumbers is much less demanding than greenhouse ones and they tolerate British weather far better, at the cost of a shorter, knobblier fruit.
• A cucumber cut and left in the fridge keeps far better than one left on the plant. Pick promptly.
• Bitterness is concentrated near the stem end and just under the skin, so peeling and trimming rescues most affected fruit.

Common mistakes

• Removing male flowers from an outdoor variety — Ridge and most outdoor cucumbers need pollination. Removing the males leaves you with aborting fruit.
• Letting the compost dry between waterings — It is the classic cause of bitterness, and one dry afternoon can affect fruit already on the plant.
• Planting out too early — Cold nights in May check the plant permanently. A cucumber set back at that stage rarely catches up.
• Letting the plant carry every fruit it sets — It exhausts itself and produces a lot of small tapering fruit. Thin to what the plant can support.

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