EFFECTS OF PLANT SPACING ON BROCCOLI YIELD AND HOLLOW STEM IN ALASKA

The potential to produce broccoli (Brassica oleracea L. spp. Italica Plenck 'Green Valiant' and 'Emperor') at high latitudes was evaluated by measuring yield, head size and incidence of hollow stem in plantings at two sites and eight spacings. The maximum yield of individual heads for fresh market was obtained at a spacing of 45 x 30 cm using single plant transplants. At this spacing, yields for Green Valiant and Emperor were 18.3 and 15.0 MT ha-1, respectively. Broccoli heads small enough to be used for processing were obtained at a spacing of 45 x 40 cm using two plants per transplant plug with yields of 21.4 MT ha-1 for Green Valiant. These yields were compared with published studies and it was concluded that there was no effect of latitude on broccoli yields or head weights. The incidence of hollow stem was low in Alaska and occurred in Green Valiant planted at wide spacings. Only plants that produced heads with the largest mean weights and mean diameters exhibited hollow stem. The use of multiple plants per transplant plug decreases mean head weight and diameter and reduces the incidence of hollow stem.