Japanese bunching onion remains a less common crop in Poland, where it is mostly grown in home gardens as a perennial plant species and used as cut foliage in early spring. Recently, some pseudostem type cultivars producing few tillers have been developed, which can be grown for the use of whole plants in early growth stages or for blanched pseudostems like leek species. This study, comprising two field trials, has been undertaken to evaluate the yield, its quality and nutritional value of cv. Performer Japanese bunching onion as affected by the growing season and age of plants. Seed propagated transplants were grown for a similar period of time from 5 Apr to 8 Jun, 6 May-8 Jul, 7 Jun-10 Aug, 8 Jul-10 Sep, 5 Aug-11 Oct or harvested 60, 75, 90, 105, 120, 135 and 150 days after planting. Plants grown for 135 and 150 days were blanched by mounding soil around the lower leaf bases. The results of the study indicated that plants of the same age harvested in monthly intervals since early June to September produced similar yields, while those in October gave lower yields, with a gradual decrease of dry matter, carotenoids, sugars, volatile oils and nitrates (V). The delay of harvest date from 60 to 120 days after planting resulted in a substantial yield increment with a simultaneous depletion of vitamin C, carotenoids, chlorophyll a+b, sugars, volatile oils, nitrates, total N, K and Ca content. Blanched plants were characterized by a considerably longer white portion of the pseudostem, lower content of chlorophyll a+b, and carotenoids, and higher amounts of vitamin C.
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