Lettuce

Wilts every afternoon despite being watered that morning

Shallow roots in a small pot. Lettuce has very little below the surface to draw on and dries out faster than anything else on the sill.

Fix: Wide rather than deep. A shallow trough gives more root run than a small round pot. Moisture-retentive mix, watered little and often.

Leaves turn bitter and a stalk rises out of the centre

Warmth. Lettuce was bred out of a bitter wild plant, and heat brings the bitterness straight back along with the flower stalk.

Fix: Hold it under 70°F if the room allows, harvest outer leaves young rather than waiting on a head, and sow a new batch every couple of weeks.

Brown crisp edges on the young inner leaves while the outer ones look fine

Tipburn. Fast growth in warm dry air outruns the plant's ability to move calcium into the newest leaves and the margins die back.

Fix: Even watering and a steadier temperature do more here than anything you can add to the soil. Move it somewhere cooler to slow the growth down, and harvest earlier than planned.