Boron (B) is a hard, brittle, brown, but light weight solid called a metalloid discovered in 1808. Its name is derived from Persian for a boron containing compound. The rest of its elemental family are all metals. It is never found in pure form. It is used for cleaning products, water softening, antiseptics, heat resistant glass, nuclear reactor rods, and transistors. Boron is a rare element and the lightest (except for hydrogen) element essential for trees. Boron is one of two essential elements (silicon is the other) usually present in a tree as a neutral molecule (undissociated form) rather than as an ion. The concentration of boron can vary widely in tissues. Its form in a tree depends upon tissue pH, existing as boric acid (B(OH)3 / H3BO3) where pH is less than 7.0 and the borate ion (B(OH)4-) where pH is greater than 7.5. Figure 1. At soil pH of 6.5 to 10.0, boron is poorly available or unavailable to trees.
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Community and Urban Forestry