This research evaluated for the NASA ALS program the effect of plant spacing on edible biomass of green salad onions. The ontogeny of Japanese bunching onion, A. fistulosum; bulbing onion, A. cepa; and chives, A. schoenoprasum grown at 10, 15, and 20-mm spacings harvested weekly were compared. Onions were grown hydroponically in Environmental Growth Chambers 16 hours light/8 hours dark, 24/20 °C, 75/99%, ≈650 μmol·m–2.
Experimental design was a completely randomized block with repeated measures. Subsamples of plants completely surrounded by neighboring plants were chosen at random from experimental units. Weekly removal of shoots began 28 days after planting (dap); destructive harvest was 70 dap. Length and diameter of longest leaf, weight (g), number of leaves/tillers were recorded weekly. Bulb caliper and weight was taken 70 dap. Bunching and bulbing onion leaves were longest at 28 dap; leaf lengths steadily decreased over time. Chives were slower to germinate and establish but at 70 dap had longest leaves of all species. Leaf diameter of all species increased as spacing increased. At 56 and through 70 dap chives at all three spacings produced more leaves. Mean weight of shoots differed significantly at the 20-mm spacing: chives weighed the least and bulbing onion the most. Bulb weight for bulbing onion and chives increased with increased spacing; bulbing onion weighed significantly more at 15 and 20-mm compared to the other species and spacings. Chives grown at 20-mm had tillering clumps of rhizomes. Total edible biomass weight (bulb, pseudostem, shoots) of bulbing onion grown at 10-mm exhibited similar ontogeny to chives grown at 10 and 15-mm spacings; bulbing onion grown at 20-mm had the most edible biomass.