If the plants are still producing good side shoot heads, you may want keep them into the winter.

I think you could get 12 plants in that bed.

Spacing depends in part on the variety of the broccoli. Some of it gets pretty big, especially if you keep it growing.

I do sq.ft spacing and normally put broccoli about 12 inches apart. The leaves will eventually overlap a little but I don't mind.

I think it can stand much less than 22 degrees if it is gradually exposed to cold, as would be expected in fall. I have had broccoli tolerate the mid-teens with no apparent damage and that was in spring. Maybe I was just lucky though, because I've heard that cold can cause buttoning and I got normal heads. Never tried broccoli in fall.

Broccoli will tolerate temperatures lower than 22F. It is about acclimation and they slowly become more tolerant to the colder temperatures in winter. I wouldn't use the row covers on them to protect from low temperatures; they may help more if used to keep it slightly warmer during the day so the plants will grow more in the winter.

It usually gets down to about 10F each winter here and I haven't lost any Brassicas due to the cold. I also haven't had broccoli plants form the head when it is this cold as well. I either plant them early enough to harvest before it is this cold, or the plants overwinter and form a head in February or March.

I usually only worry about the cold harming them when we get up to 70F and then drop back into the 30s and 20s the next day. They still hang on though.

Thank you all. This is helpful.