Most gardeners probably already know the basic tenet of garden crop rotations:
Do not plant the same vegetable in the same place two years in row.
The reason we observe this tenet is threefold:
- To avoid building up diseases in the soil.
- To hopefully make conditions less than ideal for insect pests.
- To avoid depleting soil nutrients.
Of course, we don’t want to make our crop rotations so complicated that they are no longer practical. As long as you observe the basic tenet mentioned above, you will do well. But for those of you who love planning gardens and don’t mind experimenting with more sophisticated rotations, here are a few ideas to consider.
Two plants are generally classified as part of the same family because they share similar characteristics. It follows, then, that plants that are part of the same family probably have similar effects on the garden soil. So why not take the basic tenet one step further? Let’s restate it:
Do not plant members of the same plant family in the same place two years in a row.
The most familiar examples of our slightly modified tenet are nightshades and brassicas. It is often noted that tomatoes, peppers, and potatoes (all nightshades) shouldn’t follow each other in a rotation; nor should broccoli, cabbage, and kale (all brassicas).
Other plant families generally don’t create the disease risk of nightshades and brassicas, but it’s still a good idea to avoid repeat plantings of the same families in the same spot when planning a garden.
Leaf Crop, Root Crop, Fruit Crop
Another way garden plants can be (roughly) classified is by the part of the plant we eat. Do we eat the leaves (lettuce), the roots (carrots), or the fruit (tomatoes)?
It is interesting to note that leaf crops tend to use more nitrogen than the other two groups, root crops use more potassium, and fruit crops use more phosphorus. If our primary goal is to avoid soil depletion, we should try to avoid drawing on the reserves of the same nutrient two years in a row. For example, if we have a row of carrots running along the south side of the garden one year, we probably don’t want to put potatoes there the next year, even though carrots and potatoes are not in the same family.
A third way we can approach crop rotations in the garden is to consider the role of beneficial plants. Naturally, all garden plants are probably beneficial from the gardener’s perspective, but some plants help the garden in some way, as well. For example, peas and beans fix nitrogen from the air into the soil, while marigolds exude natural insect repellents from their roots.
Of course, we don’t understand yet all the different ways garden plants interact with each other and with the soil. But perhaps we can adapt what we do know into strategic crop rotation plans. For example, after a large harvest of lettuce (a leaf crop, which means it uses a lot of nitrogen, remember?), we might replace the missing soil nutrients by planting peas in that spot. Farmers use this type of thinking to plan field crop rotations; why not try it out in the garden?
Again, these rotation plans could easily become too complicated to use, which is not desirable or helpful in any way. If your garden is in overall good health, you should have plenty of leeway to make a few rotation mistakes, so keep it simple to start. As your gardening skills improve, so will your rotation strategy. Good luck!