Q.What Causes Broccoli to Flower Quickly?
I bought some seedlings in April and the heads are flowering. The heads look thin; not like the firm one at a grocery store.

Certified GKH Gardening Expert
Most likely the heat. Broccoli needs cooler temps to grow properly; otherwise, the plants will bolt. These articles should be of some help: https://www.gardeningknowhow.com/edible/vegetables/broccoli/how-to-grow-broccoli.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/what-is-bolting-what-it-means-when-a-plant-bolts.htm
https://www.gardeningknowhow.com/edible/vegetables/broccoli/bolting-broccoli-growing-broccoli-in-hot-weather.htm