Answer: Onions can sometimes be tricky to grow because they are photoperiodic plants, meaning they regulate their stages of growth by the duration of the light/dark cycle. An onion plant will make top growth until the critical light duration is reached; then it begins to form bulbs. The amount of growth and development prior to bulbing will determine the bulb size. You need to match the onion variety with your locale -- there are "short-day" onions for southern areas, and "long-day" onions for northern regions.
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