Physiological disorders
Bolting
Bolting or premature flowering is induced in young plants by cold weather followed by warmer conditions in spring. Its impact may be reduced by growing varieties which have some bolting tolerance or by raising seedlings in a heated greenhouse and harvesting early before the seedstem has had time to develop.
Black heart
Black heart appears as a blackening of the tips and edges of young leaves in the centre of the plant, especially in hot, cloudy, humid weather. Calcium nitrate sprayed at high water volume to ensure penetration to the growing points of plants may help to minimise the severity of black heart (see Table 1).