UNITED STATES—Vegetables are greedy as they grow. They crave rich soil. They exploit it and abandon it at the end of their season. Nutrient depletion can be a problem for subsequent phases of similar vegetables. In other words, vegetables of any particular family consume the same nutrients. Each phase leaves a bit less for the next. Crop rotation disrupts this process.
Different types of vegetables deplete different types of nutrients. This is an advantage for a vegetable garden. Tomatoes can deplete soil nutrients for subsequent tomatoes. Corn, however, may not notice such depletion. It craves different nutrients, some may be content with what tomatoes did not consume. This is how and why crop rotation is so effective.
Crop rotation is simply a technique of not growing vegetables where similar types grew. Vegetables grow better where different types grew previously. Their formerly depleted but vacated soil can recuperate in their absence. They can return to the same soil after three years or so. Other vegetables that grow there for that time accelerate recuperation.
The benefits of rotation are more evident among warm season vegetables.
Warm season vegetables are generally more consumptive than cool season vegetables. That is because so many of them are actually fruits, such as tomatoes, corn and squash. More cool season vegetables are truly vegetative, such as lettuce, cabbage and carrots. Because they produce no bloom, seed or fruit prior to harvest, they need less resources.
Therefore, warm season vegetables are more responsive to crop rotation. Most are not relatives of the cool season vegetables that they are now replacing. Similar vegetables of the previous few summers are more of a concern. Tomatoes, eggplants and chilis are all of the Solanaceae family. They should avoid soil that their relatives used previously.
Similarly, if possible, corn should not grow where it grew within the past few years. Nor should beans. Fertilizer can compensate somewhat for soil depletion where rotation is impractical. For example, a fence may perpetually be the ideal support for pole beans. Spring lettuce, carrots and other vegetative vegetables may be less reliant on rotation. Although most squash benefit from rotation, zucchini seems to be productive regardless.
Highlight: Lettuce
Warm season vegetables are replacing cool season vegetables about now. Technically, lettuce, Lactuca sativa, is a cool season vegetable. It grows through spring and autumn though. The last of it can continue almost until May. Within the mildest coastal climates, it can continue later. By the time it finishes there, it is almost time to plant more for autumn.
After thousands of years of cultivation and breeding, lettuce is now remarkably diverse. Most popular varieties are leaf, head or romaine types. Leaf lettuce is mostly green, but can be bronze, reddish or irregularly blotched. Most varieties develop loosely ruffly foliar texture. Romaine and head lettuce is denser but larger. Some grow a foot high and wide.
One commonality among lettuce varieties is that they tolerate neither frost nor arid heat. Some are a bit more tolerant of one or the other, which can prolong their season. Some of the larger romaine and head types need nearly four months to mature, though. Only a single phase matures within each season. Smaller types might mature in about a month.
Tony Tomeo can be contacted at tonytomeo.com.
