Growing onions - Knowledgebase Question

Independence, IA
Avatar for dtoale
Question by dtoale
January 8, 1999
We live in the Midwest in central Iowa. Can you give me some tips on growing onions and how I can get them to grow large bulbs? We have good black dirt so possibly our soil is too rich? Any help you may have would be greatly appreciated.

Answer from NGA
January 8, 1999
Sounds as though you've had an onion crop failure. Onions do their best growing in cool weather. In fact, you can generally expect top growth in the warm months and bulb growth in the cooler months of the year. There are some cultivars that require 13-16 hours of summer daylight and some cultivars that thrive with only 12 hours of daylight. If you purchase onion sets (as opposed to seed), look for bulbs that are 1/2" in diameter. larger bulbs tend to bolt and set seed before producing decent sized bulbs. Plant onion sets 4-6 weeks before the last frost in your area. Once the soil warms, mulch to keep down competing weeds and help the soil retain moisture. Onions need at least one inch of water per week during the growing season. At the end of the season, when the tops begin to yellow, bend them down to stop the sap from flowing into the stems. This diverts the energy into the bulbs, rather than the tops. A day or so later you can harvest, laying them on the soil to dry. Once the skins are thoroughly dry, brush off any excess dirt and store your onions in a cool, airy place. Onions that perform reliably well in your area include 'Yellow Sweet Spanish, 'Yellow Globe', and 'White Sweet Spanish'.

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