A quick overview of why plants can benefit from a cold snap. It’s kind of like a board game where the aim is to accumulate degree days. So one degree day is one day spent below a given temperature which varies from plant to plant. 1 day at 6 degrees below is worth 3 days at 2 degrees below. When the critical number is reached then the plants will move onto the next phase in the cycle. This tends to be a feature of long day plants.
These leafy vegetables really cross over between annual and the perennial approach to gardening beloved by permaculturalists. As long as you keep picking them they remain vegetative – sorrel does that too and its a really useful thing for intelligent gardening.
If you really want to know how plants operate you owe it to yourself to get hold of these books. I used them extensively as reference books in putting this site together and I know enough about the science to really appreciate what they did in making this great body of knowledge accessible.