Bitter fruit

What you see

The fruit tastes intensely, unpleasantly bitter - usually strongest at the stem end and just under the skin. The plant looks perfectly healthy.

Conditions

Stress: irregular watering, heat, cold nights, poor soil or a plant left to go too long between pickings. In courgettes and squash it can also come from a plant grown from saved seed that crossed with an ornamental gourd.

Treatment

Taste a small piece raw before cooking a whole fruit. Discard any strongly bitter fruit - eating it can cause serious stomach upset. Correct the watering and the next fruits are usually fine.

Prevention

Water deeply and evenly, mulch, and pick regularly. Never save seed from courgettes, squash or cucumbers if ornamental gourds were grown nearby.

Months: June, July, August, September

Plants

Cucumber, Marrow / Courgette, Butternut squash, Melon

Remedies

Mulch

The thing people get wrong

This is the only garden problem on this list that can genuinely make you ill, and it is routinely dismissed as a quirk of flavour. Cucurbitacin poisoning - toxic squash syndrome - is real. The rule is simple and worth teaching everyone in the house: if a courgette or cucumber tastes properly bitter, spit it out and throw the fruit away. Do not cook around it.