Edwin Tidmarsh, horticulturalist, was appointed curator of the Grahamstown Botanic Garden around 1870 and held this post until at least the end of 1904. In its Report on the gardens for 1872 the committee stated that it "cannot speak too highly of the valuable services of the present curator, Mr Tidmarsh" and four years later again recorded a vote of thanks for his energy and zeal.
In 1882 Tidmarsh became a foundation member of the Grahamstown Horticultural Society and was elected on its first management committee. Years later, in 1897, the Grahamstown and Albany Horticultural Society was formed and again Tidmarsh served as a member of its committee. In March 1889 he compiled A catalogue of roses... (Grahamstown, 1889, 18p), listing roses for sale at the Botanic Garden, with a preface containing remarks on their cultivation. He also contributed some notes to the Agricultural Journal of the Cape of Good Hope in 1892. During 1889 he assisted Dr. Selmar Schonland*, Director of the Albany Museum, in forming a collection of economic plants and their products. Two years later he again assisted Schonland, this time in efforts to breed ladybird beetles (Rodolia sp.) that prey on the so-called Australian bug, the scale insect that threatened local citrus trees. In 1900 he presented a block of cork-oak (the European oak, Querius suber) from the botanic gardens to Albany Museum. That year he also reported to the entomologist of the Eastern Cape, C.W. Mally*, on the damage done by the fruit moth. Mally published an article on the subject in the Agricultural Journal (1900).
Over the years Tidmarsh sent many living plants and seeds to the Royal Botanic Gardens at Kew, England. The species Aloe tidmarshii was named after him by Schonland*. His grandson, Charles E.M. Tidmarsh, became a pasture ecologist.