EFFECTS OF PLUG TRANSPLANTING ON GROWTH AND BOLTING OF SPINACH

Plug-transplanting culture of spinach (Spinacia oleracea L.) has been studied as a method of making seedling emergence uniform, promoting initial growth, and reducing the damage caused by soil-borne diseases in summer in Japan. However, it has been suspected that transplanting will cause bolting of spinach plants before they reach marketable size (a 20-cm maximum leaf length is preferred in Japan). In this study, the effects of transplanting, root pruning, and soil water conditions on the bolting and growth of early-bolting cultivars were investigated. Transplanting and root pruning did not affect bolting rates. Soil water deficit after transplanting appeared not to affect the number of days from sowing to the start of bolting. However, the bolting rate in water-deficient plants was greater than that in sufficiently irrigated controls at the same maximum leaf length. Water-deficient conditions thus limited leaf expansion and delayed harvest. Limitation of leaf expansion due to water deficit after transplanting appears to be one of the factors causing bolting before spinach plants reach marketable size.