Crop rotation is a term more commonly associated with farmers – although increasingly less so in the modern age of monoculture and industrial food production. It is a practice that farmers for many thousands of years utilized to preserve the health of the soil and their crops. It is actually a technique that can be applied on any scale, and it is ideally suited to permaculture plots for the benefits it brings. The idea of crop rotation is that different plant species are planted in different areas of the garden bed in successive seasons, so no plant is in the same patch of soil for more than one crop growing cycle. There are several benefits to crop rotation.
Perhaps the primary reason to use crop rotation is that it prevents the build up of diseases in the soil. Many pathogens and harmful bacteria affect a certain species or family of plant. If the same plant is grown in the same area of soil for several growing seasons this allows the disease time to build up and can eventually lead to crop failure. By rotating the crops, with different families following one another, these harmful microorganisms are kept in check. The same goes for potentially damaging pest insect populations. Many pests favor particular species or families of vegetable or fruit. For instance, potato beetles will, besides potatoes, also eat plants in the same family such as eggplants. By rotating crops you deprive the pests – which often overwinter in the soil – of a consistent supply of their favorite foods, and so populations are kept in check.
It is not simply preventative measures that crop rotation provides the permaculture plot; it can also have a positive impact on the quality and health of the soil. Different types of plants require different combinations of nutrients. Some may be heavier nitrogen feeders, for example, while others require a soil with lots of carbon. Different plants also prefer different soil alkalinity or acidity. Thus, if you plant the same species of plant in the same position, they may deplete the soil of certain nutrients. By rotating crops you not only avoid doing this, but you can use the plants themselves to maintain the nutrient balance in the soil. For instance, you plant heavy feeders of nitrogen in a position that in the previous growing season was planted with nitrogen fixing species. Some plants also improve the quality of the soil, by adding organic matter or by varying root depth so that the soil structure remains ideal for moisture percolation and aeration.
The precise way you practice crop rotation will depend upon the conditions unique to your site, such as soil health and climate, as well as the crops you wish to harvest. However, there is a standard four-bed crop rotation for vegetables that can act as a point of general guidance in which types of plants most benefit from following one another.
There are four groups of vegetable plant families that are rotated through the beds in a cycle over four years. The plants species within these families have similar nutrient needs and interactions with the soil and insects.
The first group is the brassicas and other leafy vegetables that are grown for their leaves. This group includes kales, cauliflowers, Brussels sprouts, spinach, lettuce and broccoli. These are heavy feeders of nutrients.
This is the legume group, and includes vegetables such as broad beans, peas, okra, peanuts and cover crops such as alfalfa and clover. These plants fix a lot of nitrogen in the ground, which is why they follow the first group whose heavy feeding habits will have depleted the soil of this essential nutrient.
The third group comprises the allium family, which includes onions, leeks, shallots and garlic. These plants like a nutrient rich soil with lots of organic matter, so follow the legumes who ad nutrients to the soil and can, if cover crops are slashed and left to rot into the soil, add rich humus to the topsoil.
The fourth group comprises rooting and fruiting vegetables, such as carrots, beets, radish, onions, potatoes, corn, tomatoes and capsicums. The root systems these plants develop help improve the quality of the soil structure by penetrating deeper into the soil profile. Thus, they are followed by legumes, which prefer a loose soil to grow in.
In Year 1 bed one will contain the brassicas, bed two will be planted with the rooting and fruiting crops, bed three will house the alliums and bed four legumes. The second year sees the legumes moved to bed one, the brassicas to bed two, the rooting and fruiting plants to the third bed and the alliums to bed four. In the third growing season in the succession the set-up will be as follows: bed one will contain alliums, bed two the legumes, bed three the brassicas and the fourth bed will be planted with rooting and fruiting crops. In the fourth and final year of the succession plan, bed one is planted with rooting and fruiting varieties, bed two has the alliums, bed three the legumes and the fourth bed plays host to the brassicas.
This is a simple guide to crop rotation, and you can adapt it to suit your tastes, climate conditions and size of your plot. However, it is generally a good idea to avoid planting the same family of vegetables in the same location any more frequently than once every four years. This gives the soil the opportunity to retain its balance and avoid depletion of nutrients. Is you are trying to repair soil, you may also want to plant a bed with a single cover crop to replenish nutrients, or indeed factor a fallow year for each of your beds into the plan, so that nothing is grown in it and nature can act upon the soil as it sees fit.