Crop Rotation
Episode #4 of the course Advanced gardening by Alice Morgan
Hello! Yesterday, we talked about cover crops. Today, we’re moving on to a related topic: crop rotation. Crop rotation is method of crop management that moves different plants around the garden from year to year to decrease problems with pests and diseases and increase soil fertility. It’s particularly important if you want to minimize the use of pesticides in your garden, because you won’t need to rely as heavily on chemicals to manage problem infestations. Let’s look at pests and and fertility separately.
Pest and Disease Management
Many pests and diseases don’t die at the end of the garden season with their plant hosts. For instance, potato beetle larvae overwinter in the soil. If you plant potatoes in the same area that was plagued by beetles last year, the larvae from last year will emerge and only have to go as far as your new potatoes. However, if you notice the problem early and plant your potatoes at the opposite end of the garden, you’ll be less likely to have as severe a pest problem. Crop rotation can also cut down on plant diseases, provided you know what pathogen you’re dealing with. For example, verticillium wilt is fungus that remains in the soil for up to three years and affects anything in the Solanum family. Knowing that, you can avoid planting any Solanum plants in an affected area for the three years it will take for the disease to disperse.
Here a few common plant families:
• Umbelliferae: carrots, celery, parsnips, dill
• Solanaceae: eggplants, bell peppers, potatoes, tomatoes
• Asteraceae: lettuce, artichokes
• Brassicaceae: cabbages, turnips, cauliflower, broccoli
• Cucurbitaceae: squash, melons, cucumbers, pumpkins
• Fabaceae: beans, peas, lentils
• Poaceae: corn, rice
Soil Fertility
Not all plants take nutrients from the soil in the same way. For instance, corn is what is called a “heavy feeder.” It needs lots of nitrogen and potassium to thrive, so if you plant corn in the same place every year, your soil will suffer alongside the health of your corn. However, if you move the corn around from year to year and plant a nitrogen-fixing plant, like beans, in its place, your soil nutrient level will even out.
Here’s a list of common vegetables and their nutrient requirements. Nitrogen is the most important nutrient to keep in mind. If you’re keeping it balanced through crop rotation or cover crops, most other nutrients will take care of themselves.
• heavy feeders: corn, tomatoes, leafy vegetables, fruiting vegetables
• light feeders: herbs, flowers, root vegetables
• nitrogen fixer: beans, peas, lentils, soybeans
How to Rotate Crops
The nice thing about crop rotation is that all you need to be successful is a good organization system to keep track of where things go. To get started, sit down with some paper, and decide what you want to plant and how to alternate them in the future. It might be a good idea to make sketches for each year. For the best results, you should create a plan that avoids planting anything in the same area for three to four years.
The most important aspects of crop rotation is make sure that plants in the same families aren’t planted in the same place from year to year. For optimal results, make sure you plant a nitrogen fixer after a heavy feeder and a light feeder after a nitrogen fixer. If you have soil fertility problems, you may want to alternate heavy feeders with nitrogen fixers.
Here are examples to illustrate these two ideas.
• year one: corn (heavy feeder) → year two: snap peas (nitrogen fixer) → year three: potatoes (light feeder)
• year one: corn (heavy feeder) → year two: snap peas (nitrogen fixer) → year three: pumpkins (heavy feeder) → year four: red clover (nitrogen-fixing cover crop)
I hope that you feel that you have a good grasp on crop rotation now. Tomorrow, we’ll move on to a technique for setting up your garden: wide row gardening.
Recommended books
Crop Rotation on Organic Farms by Charles L. Mohler and Sue Ellen Johnson
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