Concur: need to know the variety and growing conditions. Normal Broccoli is subject to "Buttoning" when the plants stressed. I have observed nurseries trying to sell plants that had already buttoned due to holding them in pots too long. Anything which stunts the plant will caused this and no the plant will not recover. The result is heads that rarely get larger than a half dollar. There are varieties ( sprouting broccolies) that just put out large amount of shoots with little heads 1-2 inches in diameter. In all cases tho broccoli is a large plant. If you have little plants, probability is that it is stunted. Most popular sproutng broccoli in the US is Calabrese which actually forms a small 3-5 inch central head before kicking out copius smaller side shoots. No. 80 degree weather should be no problem. Since you direct seeded crowding could be the problem. Bid plant need lots of room. They are also heavy feeders.
