The second method is crop rotation. Different crops are planted in different years in a single field. For home gardeners, allowing a garden to remain unplanted goes against the very essence of why we garden so practicing crop rotation to prevent a cycle of diminishing harvest is the best idea.
Crop rotation is used to keep soil from losing nutrients that a specific plant needs. A plant like corn needs a lot of nitrogen from the soil. When it is planted in the same spot repeatedly, it will ultimately deplete all available soil nitrogen, committing a slow suicide. On a commercial level, farmers add tons of nitrogen fertilizer to soil to artificially feed the plants. On a local level, home gardeners add nitrogen fertilizer to their soils when they notice reduced plant growth too.
Effective home garden crop rotation can drastically reduce the need for supplemental fertilization and helps maintain a healthy, balanced, nutrient-rich soil. For organic gardeners it is almost a must.
The simplest cycle is a two-crop rotation where a plant like corn is planted one year and a crop like peas is planted in the same bed the next year. Then the cycle repeats each year with corn followed by peas followed by corn followed by peas; each cycle is completed in two years. A three-crop rotation takes three years to complete. A seven-crop rotation takes seven years.
The selection of the plants for each year is the most important aspect of crop rotation. To be effective, each successive planting should grow differently than the previous planting. In the two-crop example above, corn grows in a spot, depleting soil nitrogen. The next year a legume like peas is planted to replenish soil nitrogen. Many legumes have root nodules that harbor beneficial bacteria that takes nitrogen from the air and fixes it into the soil.
I like to practice a three-year crop rotation in my garden. In recent years I've done a tomato-pea-cucumber cycle, a garlic-pea-spinach cycle, and a beet-bean-cucumber cycle. In each of those cycles I also grew vetch. Vetch can handle cold weather so I sow it in fall after I've harvested and cleaned up a bed. The vetch grows into winter and again in early spring; I turn it into the soil about six weeks before planting the new season's crops. For plants with early summer harvest, I'll sow vetch and allow it to grow during the remaining summer and early fall.
A four-crop cycle is also easy if you divide plants into groups. Fruiting plants like tomatoes, cucumbers, and pumpkins is one group. Leafy plants like spinach, kale, and broccoli is a second. Root vegetables like carrots, beets, and potatoes is a third. Legumes like fava beans, peas, and lentils is a fourth.
Another important reason to rotate your crops is to reduce disease and pest problems. Tomato plants are very susceptible to soil-borne pests and pathogens. In the first year of planting a new bed, tomatoes often do very well, but after being in the same spot for a period of years they suddenly seem to have problems with early blight, fusarium wilt, or leaf spot. The fungus or bacteria that causes many potential tomato problems lives in soil.
This works because the pathogens are plant specific; tomato disease will not affect corn, peas, spinach, or pumpkins. Crop rotation helps keep plant problems from becoming established in your garden. Before tomato pathogens develop, another plant like beans grow in the bed, then a plant like spinach is planted before bean problems develop.
Knowing what plants you want to grow and the most likely diseases in your region will help you determine the best cycle. Many fungi that affect tomatoes remain viable in soil past three years so a four-crop rotation is recommended. By the time tomatoes are planted again, the threat is gone.
It's important to be aware of plant families when planning and planting. Tomato, eggplants, and potatoes can be susceptible to the same pathogens. Tomatoes and peppers have similar problems. For that reason similar plant families should not be included in a crop cycle; avoid planting tomatoes and peppers or tomatoes and potatoes in the same bed within a single crop cycle.
I practice a three-crop cycle because it's easy to plan and easy to do. It reduces the potential for problems, but isn't foolproof. If I do encounter problems in a bed, like tomatoes, I'll make note and transform that bed's cycle into a four-crop or five-crop model.
Occasionally I get lazy or behind in planting and repeat crops in a bed. Problems don't automatically develop, but I do try to get back on track for the next year.
Home garden crop rotation also provides a great opportunity to amend your garden soil. Because you're cleaning up each bed before planting a new crop, the addition of compost is easy to do as part of soil preparation before sowing or planting. Tilling in the spent plants from the previous season, like I do with vetch, also adds important organic material to soil.
The combination of crop rotation and soil amending acts to maintain a healthy soil environment. Beneficial soil bacteria and organisms thrive while harmful ones diminish and the microorganisms help make soil nutrients available to plants, enhancing overall garden production.
It does take a minimal amount of extra time to plan and initiate a new crop cycle. Depending on the size of your garden you may have to forgo certain crops in some years if there isn't enough space for a complete cycle for all garden plants. I accept these limitations as a tradeoff for a better garden overall. Occasionally doing without chard or parsnips or butternut squash is okay.
Home garden crop rotation is easy to do and has many benefits. While you're planning your next garden, think about doing it a little different than last time.