My experience is that the more full sun exposure and your ability to raise ambient temperatures at ground level make a huge difference on getting good growth of these sorts of crops, even in my much balmier zone 9b/10a climate. Top growth seems to just stall for most this time of year if you can't warm things up during the day.

Thanks, Bahia, Cabbages and broccoli that are were pretty strong plants before it cooled off are doing well.Next year I will try to do better earlier, with varieties of different maturity dates for each crop. I am getting my low tunnels together but I still think things will be slow.

Succession planting in the same bed mainly involves being practical about how much soil nutrition and fertility you are losing with each planting, then replacing it. I remove all the roots and organic debris, then add lots of finished compost and compost tea before germinating a new crop. I use seaweed emulsion for micronutrients and then read my plants' growth to see any signs that I've miscalculated.

If you suspect you are carrying generations of diseases from crop to crop, that's a bigger discussion.

Those are really good tips, dicot.By succession planting, I was more referring to planting the same crop in vacant beds every so many days through the winter.