Doubling of onion bulbs as affected by size and planting date of sets

The effect of size of sets and planting dates on the frequency of double bulbs was investigated with two early onion cultivars. The two cultivars varied significantly in their performance, with the cv. Beit‐Alfa being more prone to doubling than the cv. Ori. Bulbs developing from large sets produced more shoots per bulb and showed a higher percentage of doubling in the field. Environmental conditions changing with planting dates significantly affected the tendency for axillary shoot development. The effect of genotype and environmental conditions on doubling is discussed.