[3] The bark is taken from young branches and twigs in oak coppices and can be up to 4 mm thick; it is grayish-brown on the outside and brownish-red on the inner surface.
[4] In some areas of the United States, such as central Pennsylvania and northern California[citation needed], "mulch" is often called tanbark, even by manufacturers and distributors.
[citation needed] In America, condensed tannins are also present in the bark of blackjack oak (Quercus marilandica).
[5] In New York, on the slopes of Mount Tremper, hemlock bark was a major source of tanbark during the 19th century.
[6] Used tanbark is employed in horticulture and spread on flower beds and in glass houses to keep down weeds and protect plant roots.