Greenhouse-grown Transplants as an Alternative to Bare-root Transplants for Onion

Abstract

Commercially produced bare-root onion (Allium cepa L.) transplants may not be uniform in size and require a period following planting in which to begin regrowth. There is little information on how, when established in the field, plants developed from greenhouse grown onion transplants differ from those that develop from bare-root transplants. Development and yield for onions grown from bare-root transplants were compared to plants produced from transplants grown in single cells with volumes of 36 or 58 cm3 in seedling production trays in a greenhouse. `Texas Grano 1015Y' and `Walla Walla' onions were established in the field with commercially available bare-root transplants or with greenhouse grown transplants produced in trays. Bare-root transplants were heavier than 8-week-old greenhouse grown transplants. Fresh weights of transplants produced in 58-cm3 cells were heavier than those from 36-cm3 cells, but dry weights were similar. From when about 20% of onion tops were broken over, onion bulb diameters did not increase sufficiently to justify delaying harvest until 50% of tops had broken over. Yields of `Walla Walla' were better than those of `Texas 1015 Y' and yields from plants developed from seedlings grown in 58-cm3 cells were similar to those from plants developed from bare-root transplants and better than those from plants developed from seedlings grown in 36-cm3 cells. Individual bulb weights of `Texas 1015 Y' were not affected by transplant type and averaged 162 g. Individual bulbs for `Walla Walla' from plants developed from bare-root transplants and those produced in 58-cm3 cells were similar in weight (averaged 300 g) and were heavier than those from plants developed from transplants grown in 36-cm3 cells (240 g). Greenhouse transplants produced in trays with the larger cells may provide an alternative to the use of bare-root transplants, if transplant production costs are comparable.