Garden plants require small amounts of boron for proper growth. A lack of boron stunts plant growth and results in decreased yields.
Boric acid is applied to the soil. It may be mixed with water and other fertilizer and worked into the garden before planting. One application of boric acid, which is about 11 percent boron, will usually last for three growing seasons, according to the University of Idaho.
Too much boron in the soil can become toxic. The South Dakota State University Extension recommends only applying boric acid after a boron soil test has determined the need.
Soil pH influences the availability of boron for plant use. Boron is most readily available in soil that has a pH level between 5.0 and 7.0.
Conditions Leading to Deficiency
Boron levels are often low in coarse soils that are low in organic matter. With heavy rainfall or over irrigation, especially in sandy soils, boron may leech from the soil.