What is crop rotation?
Crop rotation, to put it simply, is the act of rotating the crops planted in your vegetable garden so that you do not plant the same vegetable family in a consistent location season after season. This practice has several benefits including suppressing pests and diseases, reducing soil erosion, and adding nutrients to your soil. Crop rotation can be intimidating to home gardeners, however; the benefits well outweigh the effort it takes to execute this century old practice (first documented in the Middle East in 6000 BC!)
Let's look into a few of the benefits of crop rotation:
Reduces soil erosion. Soil erosion happens when planting medium lacks aeration and improper drainage. Rotating your crops results in plants with different root structures creating channels through your soil and enhancing its ability to drain while aerating at the same time.
Limit the use of added fertilizers by utilizing nutrients already found in certain crops. "Heavy feeding" crops that need lots of accessible nitrogen (such as corn, lettuce, broccoli, tomatoes and cucumbers) should be planted in an area where "low feeders" or crops that increase soils nitrogen levels were planted the season before. (More information below in the 'The Three Feeders'.)
Suppress pests and diseases. When it comes to vegetable crops, pests and diseases are often a family affair. Broccoli and kale, for instance, are very different vegetables but they belong to the same family, so pests and diseases that plague one will often plague the other. These harmful foes can hide in your soil all Winter long, and planting a crop of the same family for them the next season is like waking them up with breakfast in bed! Instead, opt to plant a crop of a completely different family in that location the following seasons.
How often should I rotate my crops?
Ideally you can create a cycle where you rotate each family every 3 to 7 years. While that may sound like an intimidating process, you would be surprised how many vegetable families you already have planted in your garden each season (learn more about the different families below). At the very minimum one should strive to rotate every other year. If you encounter a problem with bugs or disease, this rotation should be extended to suppress the outbreak.
The Three Feeders
Your rotation plan should follow the pattern:
Heavy Feeders - Givers - Low Feeders
Heavy Feeders are crops that require an abundance of nitrogen, such as brussels sprouts, squash, pumpkins, lettuces, spinach, melons, broccoli, cauliflower, cabbage, tomatoes, cucumbers, eggplants, scallions, onions, corn and garlic.
Givers are crops that introduce nitrogen to your soil, these crops belong to the legume family (peas, beans, etc..)
Low Feeders don't take much of the nitrogen the Givers provided your soil the season before, so they are a fantastic candidate to follow the givers. Low Feeders include potatoes, parsnips, collard greens, swiss chard, carrots, beets, kale and most herbs.
Quick Tip: While rotating your crops to utilize Givers as a source of nitrogen in your soil, it is still important to test your soils nutrients often and amend as needed.
Crop Rotation Examples
The above examples show a four season cycle and follow the pattern High Feeder - Giver - Low Feeder - High Feeder. Each crop represents one season.
Example 1: Lettuce, Peas, Beets, Garlic
Example 2: Spinach, Beans, Carrots, Onions
Example 3: Tomatoes, Beans, Kale, Eggplant
Example 4: Corn, Peas, Potatoes, Brussels Sprouts
Quick Tip: While planning out your crop rotation schedule, it is also important to keep lighting in mind. Be sure not to plant tall crops where they can block lower crops from getting the correct amount of sunlight. For this reason some gardeners choose to rotate their crops by height, only growing tall crops (like corn, tomatoes, trellised squashes and pole beans) in certain areas of their garden and low growing vegetables (lettuces, beets, carrots, and onions) in another location.
Making a Plan
We've mentioned before the importance of keeping a garden journal. Beyond using it as a tool for jotting down the location of the crops you plant and whether or not you enjoyed them at the dinner table, you can also track pests and disease outbreaks, the soil and fertilizers used, and the lighting of your garden. We have a simple garden journal layout here, but you can also make your own by drawing diagrams or using computer software. Whatever route you choose, make sure to keep copies for several years so you can successfully rotate your crops. Some gardeners will pre-plan their layout for the following season(s) while planning their current one to reduce the time spent on planning the next year.
When planning out your vegetable garden, take note of which family you planted, and where, so you can plant a crop from a different family the following season.
The legume family includes beans, peas, fava beans, soybeans, chickpeas and alfalfa, as well as uncommon garden crops like peanuts and cowpeas.
Tomatoes, peppers (sweet and hot), eggplant, potatoes and tobacco all belong to the nightshade family.
Lettuce, endive, artichokes, sunflowers and salsify are all related.
This delicious family is home to garlic, leeks, onions and chives.
One of the largest families with broccoli, cauliflower, brussels sprouts, kale, kohlrabi, collards, rutabaga, turnip, mustard greens, bok & pac choy and radishes.
Cool weather crops like spinach, beets and swiss chard belong to this family.
This family houses carrots, parsnips, fennel and celery along with the herbs cilantro, parsley and dill.
Cucumbers, muskmelons, watermelons, summer squash, zucchini, winter squash, pumpkins and gourds make up this family.
Corn, wheat, rice, barley and millet are part of the grass family.
Once thought to be part of the onion family, the perennial vegetable asparagus is alone in the family Asparagaceae.