There are two traditional methods for planting vegetables: in mounds and in rows. The techniques are frequently used together, because specific types of fruits and vegetables are recommended for mound planting. The height or depth of a mound depends on your specific growing area. Pregnant women should always wear gloves when working in garden soil to protect themselves from potentially harmful bacteria.
Mound planting is a form of group, or block, planting. The traditional way to plant corn (Zea mays), for example, is to place three to five seeds in a circle 18 inches across. This circular grouping is called a mound, even if the soil is not raised. Planting in flat mounds or groups allows for growing vegetables together that have similar water and nutrient needs. In the case of corn, it also aids wind pollination.
Raised mounds tend to be the first thing a new gardener thinks of when she first hears the term. Raised mounds are useful in areas that flood, have large amounts of rainfall, or have poorly draining soil. Raised mounds are generally four to six inches high. This slight elevation helps deter people from walking on the planting area, and it ensures adequate drainage for the plants.
In extremely arid environments, mound groupings are often lowered four to six inches, rather than raised. This technique helps to capture and direct moisture to the root zone around the plants. Sunken mounds will capture more water during rain showers, and irrigation water is retained in the immediate garden area to be fully absorbed.
Raised mounds can be several feet high, and treated as a raised garden bed. The higher the mound is without some kind of containment, the wider it must be. This can make reaching the center difficult, but it's attractive when you're growing large vining plants such as pumpkins (Cucurbita maxima). Sunken mounds should be no more than six inches below the garden level, so that the plants do not drown during large rainfall events.
Whether you're creating level mound groupings, raised mounds or sunken mounds, be sure to leave several feet of space between them so you can walk through after the plants have filled in.