This is my first year growing vegetables and I sowed loads of lettuce, but most of the plants have started to grow these big, tall spikes of leaves which also taste very bitter. Am I right in thinking that they’ve bolted, and if so, what can I do to prevent this from happening again?Anna H, DublinYes, I’m afraid that it sounds like your lettuce plants have bolted, a condition often caused by exposure to high temperatures as experienced recently this summer. Bolting is a plant’s response to stress, which causes it to bypass its leafy stage of growth and instead attempt to start flowering and setting seed. Unfortunately, lettuce is particularly prone to bolting, with its freshly sown seed being highly sensitive to high temperatures. Anything above 23C can act as a trigger, and once the process begins, it cannot be reversed. Bolting also dramatically changes the flavour and texture of the leaves, making them bitter and tough, so the best thing to do with your plants is to pull them out and put them on the compost heap before sowing/ planting new ones.To prevent it happening again, always sow in the cool of the evening, and avoid sowing lettuce seed during any particularly hot spells. If sowing into pots/trays, place these freshly sown containers in a cool space well away from direct, hot sunshine. Or if you’re sowing directly in the ground, then choose a shady, cool corner of your garden or allotment, making sure to keep the compost/soil damp but not sodden.Also bear in mind that some varieties of lettuce have better resistance to bolting than others. Examples include the cos-types known as ‘Little Gem’ and ‘Paris Island Cos’, the semi-cos type known as ‘Freckles’; the butterhead types known as ‘Analena’ and ‘Diana’; the loose-leaf type known as ‘Lolla Bionda’, the Batavia-type known as ‘Nevada’, and many of the loose-leaf seed mixes designed for summer sowing. Recommended seed stockists include brownenvelopeseeds.com; greenvegetableseeds.com; fruithillfarm.com and quickcrop.ie