When a plant prematurely produces a flower stalk and sets seed, triggered by heat, drought, or lengthening days. Bolting makes leafy vegetables bitter and tough. Common in lettuce, spinach, and coriander.
Bolting is a common challenge for Australian gardeners, particularly during the warmer months when temperatures spike unexpectedly. Cool-season crops like lettuce, spinach, broccoli, and cabbage are especially prone to bolting when exposed to sustained heat above 25°C. In tropical and subtropical zones, bolting can occur year-round unless you time plantings strategically during cooler periods.
To prevent bolting, plant cool-season vegetables during autumn and winter (March to August) when temperatures remain moderate. In warmer zones, sow seeds in late summer for autumn harvest, giving plants time to mature before spring heat arrives. Provide afternoon shade using shadecloth during September and October in southern regions, or extend cooling into spring where needed.
Choose bolt-resistant varieties when available—many seed catalogues and retailers like Bunnings clearly mark these selections. Water consistently and maintain soil moisture, as stressed plants bolt faster. Mulch around plants to keep soil cool and regulate moisture. In high-heat regions (zones 11-12), consider growing heat-tolerant alternatives or taking a summer break from cool-season crops.
Once bolting begins, the plant's energy diverts to flowering and seed production, making leaves bitter and tough. Harvest immediately if bolting has just started, or remove the plant and compost it to make space for heat-tolerant crops like beans, squash, or heat-loving lettuce varieties.