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onion flowersFlowers on onions are not desirable (unless saving seed), as it compromises the quality of the bulb. Flowers can be triggered by temperature fluctuations (such as a period of warmth, followed by cold, followed by warmth). A bulb uses energy to send up a flower stalk (called bolting), so once it does, the bulb will be smaller and won't be as large as an onion that does not bolt. It is still edible, but lower in quality. It is not necessary to cut off the flower stalks (some gardeners do, some don't), but you should harvest the bulb as soon as you can, and use it promptly--it will not store well. When buying onion sets, look for those that are no thicker than a pencil, and plant them out at a time recommended for your area; larger sets tend to bolt. Also, keep in mind that 1015 onions are a short-day variety; make sure that type is recommended for your area. Short-day varieties form bulbs when daylength is between 10 and 12 hours; intermediate-day (day-neutral) onions start to form bulbs between about 12 and 14 hours of daylight; and long-day varieties form bulbs at about 14 to 16 hours daylight. If a short-day variety is planted in an area best suited for a long-day type, for example, then the bulbs might form early and not get very large. A general rule of thumb for the U.S. is that northern gardeners use a long-day type, gardeners in the mid-section use day-neutral, and southern gardeners, a short-day type.

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