Mike of Tiny Farm Blog mentioned in passing that he uses a 7-year rotation scheme. It caught my eye because I, too, use a 7-year plan, and such a long rotation plan is pretty unusual, I think. My reason for it is this: We like Tomatoes, and lots of them. We really, really like Chillis. We like Potatoes, although they're quite a challenge here, being a favourite snack for Porcupine. Let us not mention Eggplant, due to my ongoing conspicuous lack of success...
So I'm stuck with trying to grow a hell of a lot of Solanums, all more-or-less related, all prone to a common basket of diseases. And I just couldn't make it work in a four-year rotation scheme. After much reading, thinking and experimentation, I came up with the following rotation plan:
- Lime well (and compost if it's a new bed) then plant Legumes.
- Compost well with very good compost2, planting Brassicas.
- Compost if the bed needs it, and plant Onions, Leeks, Celery, Fennel.
- Supplementary compost, lime or gypsum if needed, to support The Tomatoes.
- Roots -- Carrots, Turnips, Beets. By now all that compost is very well broken down, leaving the soil deep and soft.
- Lime/gypsum according to pH, and then The Leaves: Endive, Lettuce, Chicory, Chard. Also Radishes and Rocket.
- Good compost to support the Chillis.
The glaring omission are the Squash tribe; usually they get squeezed into the Brassica bed, since the Squashes are strictly a Summer thing, when Brassicas (which are Winter-proof here) tend to get neglected in favour of Summers Orgy of Flavours. Otherwise I get some of the bush varieties into the Roots bed.
Although I've managed to keep the Tomatoes/Potatoes as far apart as possible from the Chillis, I am finding that I still don't have enough space for either of them! Its challenging when you're trying to grow a dozen different Tomato varieties in quantities large enough to feed yourselves for a year.
Then, too, I've lately ramped-up on Lettuces and Asian greens (Pak Choi, Tatsoi, Mustard) to the point where one bed every seven years is just not enough. I don't sweat too much over using beds out of order for Lettuces, since they're in and out so quickly, and harbour so few pests and diseases, and demand so little of the soil, that I think it is very unlikely to cause any problems, but I already have problems with overwintering Brassica pests.
There are also a few "other things" -- Tomatillos, (we love Mexican food!) Artichokes, Parsley, Dhanya and Basil, (we use quite a bit of that trio for Pesto) seed-crops needing beds for much longer timespans -- that cause disruptions to this idealised plan, but it seems to work pretty well. The next challenge will be to work grains into the plan, and I would like to get the seed-crops better separated from the food rotation.
What's your scheme?
 Not so very many gardening books. I'm more inclined to watch the plants themselves for the lessons I need to learn.
 Not all composts are created equal. Some are mere courtesy calls on Mr Soil Structure, adding little in the nutrition department. Others are something special and deserve due reverence.