Agriculture Reference
In-Depth Information
white, brown, or yellow. Red onion varieties mostly have a mild, sweet flavor and do not store as well
as yellow varieties.
WHAT YOU'LL NEED
• 15 to 20 good-looking onions
• overwintering strategy or mild climate
• support poles or trellis
• isolation covers (if multiple varieties are being grown for seed)
Onion seeds
POLLINATION NOTES
The onion is a strict outcrosser. Its large flower heads are attractive to a diverse
array of insects, making it crucial to isolate multiple varieties to avoid crossing. Crossing with the
Japanese bunching onion is also not out of the question, but onions do not cross with chives or leeks.
Isolate multiple varieties spatially by at least 500-650 ft. (150-200 m), much more when barriers
like bushes and buildings are not part of the garden or if there are few other flowers to distract pollin-
ating insects in the garden. Use mechanical isolation when spatial isolation is not possible. Make sure
flowers cannot touch the netting of the isolation cage, lest insects pollinate flowers from outside the
cage. The European hoverfly (also known as the drone fly,
Eristalis tenax
) is the best pollinator for
isolation cages. Otherwise use mason bees (
Osmia rufa
) or blowflies (Calliphoridae spp.), though
these may only pollinate at rates around 35%. Greater success may be had by hand pollination, for
which onion flowers must be dry. Simply brush flowers with a 1.25-2 in. (3-5 cm) brush daily for 14
days (use a separate brush for each variety).
GROWING FOR SEED
Onions grow best in full sun in sandy-loam soils with good drainage and not too
much nitrogen. In temperate climates, sowing seed in spring, harvesting bulbs in autumn, and setting
bulbs out again the following spring for a summer harvest is the most reliable method for producing
seed. Do not save seed from onions that produce seed in the first year. Sow onion seed as early in
spring as possible, whether growing for food or for seed (outdoors in midspring, or start seeds in-
doors). Onion sets (dried, immature onions from densely seeded plots) can be planted as soon as the
danger of hard frosts has passed. If the growing season is too short in your area or if seed was sown
too late, grow your own onion sets, plant them out the following spring, overwinter mature bulbs in-
doors, then harvest seed in the third growing season.
Initiation of bulb formation is dependent on day length and temperature. Short-day varieties form
bulbs with 12-hour days; long-day varieties need 14-hour days to form bulbs. Select the 15 to 20 best,
most true-to-type bulbs for seed production. Dry these 10 to 12 days in a warm place with good air cir-
