Open any gardening book and it will tell you that crop rotation is a beneficial practice. The principle is a simple one. You don’t plant anything in the same place where it grew last year, and preferably not the year before that, or the year before that.
Rotating results in healthier, better-yielding crops, partly because specific pests and diseases bother specific plants, or plant families. Relocating a crop as an evasive tactic can disrupt a pest’s life cycle by removing its host — or at least making the host harder to find. Also, plants affect the soil in different ways. Some, like corn, feed deeply and hungrily, consuming lots of nutrients but bringing up minerals from below as well. Legumes like peas and beans, because they help turn atmospheric nitrogen into organic nitrogen, tend to benefit a crop which follows, and their root systems leave plentiful organic residues in the soil — good for stimulating biological activity. Big smothery crops like squash help to deter weeds. Carrots, which grow more sparsely, may leave a weed legacy in their wake.
Nature rotates crops, but in a more linear progression, with long-term perennials following short-term annual colonizers. Growing annual food crops year after year is not quite what nature intended, so to keep them healthy farmers will rotate whole fields, often alternating a leafy crop with a grass, a grain or a legume, or grazing a field with manure-producing livestock.
For the home gardener, faced with organizing several dozen little crops within a small space, crop rotation is especially challenging. People who are good at it also tend to win at chess and can draw an entire seating plan for a wedding dinner without having a meltdown. Children are great at it because they treat it as a game — an approach that might work for you as well.
To make a rotation plan, start by to dividing your vegetables into teams based on family relationships. It’s simplest to rotate family members as a block, since they require similar care. Brassicas such as cabbage, broccoli, mustard and turnips are a family. Potatoes, tomatoes, eggplant and peppers form a family, as do the cucurbits — cucumbers, squash, pumpkins, melons. The legumes are peas, beans and certain cover crops like clover and alfalfa which can be tilled in to improve the soil. The apiaceae, with their umbrella-shaped flowers, are crops like carrots, parsnips, fennel and dill. Other families are the grains (like corn), the beet group which includes spinach and chard, the asteraceae (lettuce, artichoke, chicories) and the fragrant tribe of onions, garlic and leeks.
The object of the game is to see how long you can go without repeating any of these crops, or their relatives, in the same spot.
There are two basic styles of vegetable rotation. One is a square dance and the other is a Virginia reel. In the first you divide a square or rectangular garden into equal quadrants, assigning each one to a major family — usually the first four listed above — and rotate the whole scheme a quarter turn each year. Leave plenty of space in each quadrant for members of the extra families, many of which make good fill-in crops.
In the reel-type rotation, the garden is laid out in parallel rows. You still group plants by family, with a crop assigned to each row, and the whole thing marches a row or a few rows to the right each year, with the last row jumping back to the opposite end, just like the lead couple in a Virginia reel.
The game becomes more complicated and interesting, if you are interplanting one crop with another (spinach amid the corn, for instance) and if you practice succession cropping, in which spring peas might be followed by tomatoes, and tomatoes by fall kale. If your tall beans and corn have just been rotated to the south side of the garden, you’ll need to use their shade to protect heat-averse crops like lettuce. If you really delve into this game you’ll learn that brassicas like to follow onions, that corn is good for following peas and preceding potatoes. If you can work some cover crops into your plan, plus a two-year crop such as strawberries, you’ll approach the level of Grand Master.
Fail at the game and your garden will still probably thrive, as long as you give it nice loose soil well supplied with compost and other forms of standard garden TLC. At the very least, it’s always good to watch out for especially pest-prone crops and choose new locations for them.
The materials for this project are simple ones. You can use a pad of graph paper, or a computer, a stack of 3-by-5-inch cards, some crayons, colored Post-its, or even a big sheet of paper on the door of the fridge, with veggie-shaped magnets to label the beds. You’ll need a written record of what you actually planted, followed by a photograph of what actually came up. Begin it now, while the garden is still bare, maybe on Saturday morning when the kids are home. They’ll probably have it done by lunchtime.