I'm not sure about the timing of your planting. Cold temperatures strongly induce flowering in these plants. I'm not even sure that removal of the flower stalk could have prevented this process.

Once this plant flowers heavily and goes to seed, it will no longer devote energy to bud (sprout) development. Seems like these plants should be planted in the late summer for fall harvest or in the early spring for summer harvest.

Here is a link that might be useful: {{gwi:1246179}}

Thanks. Ours never had anything resembling the load of brussel sprouts in that picture. I must have planted these too late. They survived the winter OK but never had any sprouts. Will now harvest the seeds and try again in August.

If you planted a nice hybrid cultivar, then I suggest against harvesting seeds for a future crop. Your plants will not develop true from the seed.

Take a look at your local planting guides carefully. In your area, you will want to plant so that you are HARVESTING in the fall/winter...........or in the late spring. You don't want your plants to overwinter.