Crop rotation is the practice of not growing plants where similar plants grew the previous year.
This practice prevents the build up of pests and diseases and optimizes the use of soil nutrients. Plants from different “families” need different amounts of nutrients and their root systems also penetrate the soil to different levels. To simplify, we try to alternate between leaf crops and root crops. Leaf crops tend to be heavy nitrogen feeders with fairly shallow root systems. Root crops usually require more phosphorus and potassium and need deep soils in order to grow properly.
Different plant families also prefer different soil pH levels, so the rotation plan includes planning lime applications.
PH preferences are: Higher pH (limed) Lower pH (acidic)
Brassicas, Solanum Salad, Potatoes, Spinach, Root crops, Squash, Alliums, Peas & Beans
Brassicas: include cabbage, broccoli, cauliflower, Brussels sprouts, mustards, kale, kohlrabi and Chinese cabbage.
Roots & Solanum: The root crops include carrots, beets, & radishes; the solanums are made up of tomatoes, eggplants and peppers. Alliums include onions, leeks and garlic.
Squashes and Salad: include cucumbers, melons and Summer & winter squashes, as well as salad greens like lettuce, radicchio and endive.
Potatoes love acidic soil.
To optimize space, practice a four year rotation. In year one, grow brassicas and heavily lime the soil to increase the pH. Year two, the roots and solanums are still using the residual lime. Year three, the squashes and salad greens are enjoying the slightly more acidic environment. Year four, potatoes are grown when there is the least amount of lime left and the soil is wonderfully acidic for them.
Other crops such as spinach, corn, onions, and celery can be used to increase the number of years in the rotation.
There are many times, however, when we just one spot where we can grow tomatoes or where the trellis for peas is permanently in place. If you are short of rotation places, seriously consider moving the soil instead of the plants. It’s a bit of work with the shovel and wheelbarrow but well worth it when you see the improvement in the health of your plants.