Some of you may have noticed some new signs around the Mt. Vic garden beds. They, say things like ‘Brassicas’ and ‘Green Crop’. These signs are the first steps in a new crop rotation system we are putting into place in the garden! What is crop rotation, you might ask. Well, crop rotation refers to the practice of moving crops around your garden instead of growing the same plants in one location year after year. There are two main reasons to rotate crops in your garden. The first is to discourage soil-borne pathogens and pests that attack and weaken plants. Basically, every plant is host to specific pathogens, and these pathogens build up in the soil over time. By rotating plants you remove the pathogens’ host and eventually they will die.
The second reason is to avoid the depletion of soil nutrients and minerals. If plants that require similar nutrients and minerals are planted in the same location the soil can become exhausted and the plants won’t be as healthy. Different plants also add certain nutrients and minerals back into the soil, so rotation also nutritionally improves soil in addition to preventing nutrient and mineral depletion. A classic example is planting tomatoes after any type of legume, like broad beans. Legumes add nitrogen to the soil, while tomatoes are heavy nitrogen feeders, so planting legumes prepares the soil for the nitrogen demands of tomatoes. A third, less commonly identified reason to rotate crops is to create deeper, better aerated soils due to root penetration.
There are a few different crop rotation systems, but any one of them will be beneficial for your soil and your plants. Most recommend avoiding planting the same crop in one location for two to three years. One system divides plant based on botanical classification, i.e. Cucurbit family (cucumber, squashes, melon), Nightshade family (tomato, potato, egglant, peppers), etc. Another divides plants more broadly into three main types based on their nutrient demands; ‘light feeding’ root crops (potatoes, kumara, carrots) and herbs, ‘heavy feeding’ leafy and fruiting crops (tomatoes, brassicas) and ‘soil building’ peas, beans and other legumes. At Innermost we have divided beds into brassicas (cabbage, broccoli, etc.), nitrogen fixers and light feeders (legumes, salad, herbs, etc.), root crops (also light feeders), heavy feeders and green crops that are used to condition the soil (like lupins, mustards and grains). As we rotate these different crop types through the garden the signs will move with the, so keep your eyes out for moving signs!
If you don’t have enough space in your own garden for a full crop rotation, don’t worry. Just try to avoid planting the one crop in the same location year after year, and make sure that you replenish the soil with plenty of compost between plantings. If you would like more information on crop rotation most gardening books have at least a short section devoted to the subject, and their are many resources online, like the one below. Happy gardening!
Crop rotation article from the NZ Herald: http://www.nzherald.co.nz/