We've had a few hard frosts at night and the allotment is transformed. Squash plants deflate like a popped balloon. Runner beans turn black and limp. It's time to tidy up.
Spent plants can be put on the compost heap or dug directly into the ground. Beans in particular do a lot of good because they capture nitrogen from the atmosphere and "fix" it in the ground. You can pay a lot of money in a garden centre for nitrogen-rich fertiliser. Or you can just plant some beans and wait a season.
I'm fuzzy on the science, but I know these curious nodules on the beans' roots are involved (see the photo). The bottom line is - plant beans, dig them into the ground when they're finished, and put brassicas in the same earth next time. Brassicas love the nitrogen.
If you can't remember the order of the 4-crop rotation, try this mnemonic "Roots [point to ground, where roots grow], pots [point to your boots, like plant pots for humans], legs [point to your legs], bras [you can invent your own gesture for this one]". That's the order - roots, pots, legs and bras. Root veg first (like carrots, parsnips etc.), then pots (potatoes), next legs (legumes i.e. beans and peas) and finally bras (brassicas, that's cabbage, sprouts etc). Then you're back to roots again.