Answer: Brussels sprouts need about 100 days to mature, and they grow best in cool weather. Summer heat can make them flower and go to seed instead of producing tasty little sprouts. If you have a long, hot growing season, Brussels sprouts are best planted very early in the spring so they will have a chance to mature before the hot weather sets in. Or, plant your seeds in July so the sprouts will develop in the cool autumn weather.
If you're finding transplants in local nurseries now, by all means plant them as soon as you get them home. The will grow and produce before really warm weather arrives.
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