Food Plant Sustainability Design Guidelines

Soil Fertility

• Essential to any garden design is the principle of building soil fertility to support healthy plants. Sustainable agriculture replenishes nutrients depleted from the soil by growing food crops. One good source of nutrient replenishment is animal manure. Manures contain undigested plant fibers, or cellulose, because most animals cannot fully digest plants. Acting alone, manure can’t add nutrients to soil. However, bacteria and fungi digest cellulose in manure after it is incorporated into soil. This microbial action restores soil fertility and makes nutrients available to plants.

Synthetic vs. Organic

• Synthetic nitrogen fertilizers enrich soil with necessary nitrogen, but they do not build organic matter. Using green-manure cover crops and worm castings meets two goals of sustainable design: adding nitrogen to soil and building organic matter. Green manure is not animal manure. It is the product of growing living plants as cover crops that returns nitrogen and nutrients to soil after tilling. Jeff Schalau of Arizona State University says that using worm excrement, or castings, is a valuable sustainable agricultural practice. George Dickerson of New Mexico State University says that castings can contain up to 11 times more nitrogen than garden soil.

Crop Rotation

• Over successive growing seasons, sustainability declines when gardeners grow food plants from the same family in the same location. Same-family plants have similar nutritional requirements and deplete soil of the same nutrients. This leaves soil nutrient-poor to sustain similar plantings year after year. The University of Delaware recommends not growing same-family plants in the same location for 3 to 5 years. For example, tomatoes, potatoes and peppers are in the Solanaceae family. Applying crop-rotation principles, gardeners would not grow tomatoes year after year in the same garden plot, and they’d also not plant bell peppers in the same garden plot where they grew tomatoes 3 to 5 years before.

Insect Control

• Food-plant sustainability design guidelines are incomplete without considering responsible pest-control measures. Some botanical pesticides, such as pyrethrum and neem oil, are plant derivatives. Pyrethrum is an extract of chrysanthemum flowers, and neem oil is an extract of the neem tree. Bacillus thuringiensis (Bt) is formulated from species of bacteria, and one formulation of spinosad is derived from digestion secretions of a soil-borne bacterium. All methods do not control all insect pests, but label information on organic products indicates appropriate measures for insect-specific problems.