Most annual crop growing systems benefit from some sort of rotation, where you grow different crops in the beds from year to year so that you don’t get a build up of pathogens and a depletion of specific nutrients. Your rotation can last three or four years, and there is lots of information available on how to plan; for example the Royal Horticultural Society give a brief outline of both three- and four-year rotations here. In practice, many vegetable gardeners either do not have the space to practice a rigorous rotation (for example not growing potatoes at all, or only growing them in containers) or simply can’t be bothered.
In my small garden, I could be strict with a four-bed rotation as I do have four raised beds. However, I’m not consistent with the crops that I grow, so sometimes I want more than a quarter of the space given over to one type of crop and sometimes less. Also, I like mixing crops in the same bed, which sort of puts a spanner in the works. And anyway, I’m just too disorganised. I like to be creative and spontaneous, so basically I plant what I feel like where I feel like with the proviso that I don’t plant either onions or potatoes in the same place two years running. In fact I try out new crops each year and some of the less conventional ones (like Aztec broccoli or oca) almost certainly have fewer diseases than the standard offerings and different nutrient demands. I do try to move my beans around each year because (a) they always get a healthy dose of compost dug into their bed before planting and (b) they are nitrogen-fixers, so should help boost the fertility of the place they have been.
In addition, in my garden, I do lots of container growing. I make use of loads of home-made compost for this purpose and, of course, it doesn’t just get used once.You can’t, however, plan a rotation for your pots in the same way as for land. Last year I used lots of my fresh compost for potato-growing in dumpy bags. After I harvested the potatoes, I left the compost in the bags, but folded the tops down to protect it. I don’t want to grow potatoes in the same compost this year, so that has been transferred into some big pots for growing mangetout up the fence. Compost that has had tomatoes or peppers growing in it usually gets transferred into a bed that will be used for squashes. Because tomatoes and potatoes both get blight, I try to avoid transfer of spores in compost so don’t use compost from tomato pots in potato beds.
It all sounds quite complicated, but actually, I don’t have any difficulty remembering what I grew where (especially since I always take lots of photos) and deciding where to plant. I’m sure there are some of you out there who love an organised rotation, but you are clearly not scatty like me!