The pattern of frost‐hardening of leaves of winter cauliflower (Brassica oleracea var. botrytis cv. Clause 30)

Summary The suitability of an electrical conductivity assay of leaf material for determining frost hardiness in winter cauliflower was established. The assay was used to monitor the changes in hardiness of field‐grown plants during two seasons at two sites. Levels of frost hardiness were related to mean air temperature over the 7‐day period prior to sampling (r = 0.6008, P< 0.001). There was no clear disjunction of any temperature to indicate a threshold temperature of hardening. Dehardening occurred in spring and during mild spells in winter. In the mild regions where this crop is grown commercially it is likely that plants are not fully hardened for much of the winter. This may facilitate curd growth but may put the crop at risk from frost damage.