From 1796 to 1823 he mainly resided at Clapton, and, as he had grown hardy plants in his home at Walthamstow, then devoted himself to greenhouse exotics, giving assistance to the Loddiges family in establishing their nursery in Hackney.
[2] He has been honoured in the name of Sedum fosterianum, which was first published by Sir James Edward Smith in English Botany (Engl.
[2] Between 1775 and 1782 Forster made many drawings of plants, studying exotic species in the garden of Thomas Sikes at Tryon's Place, Hackney.
In 1784 there was printed a list of additions to Richard Warner's Plantæ Woodfordienses, attributed by Dryander to Thomas Forster.
A 14-page list of the rare plants of Tunbridge Wells, c.1800, is attributed to him by Dryander; and in 1816 he published a Flora Tonbrigensis, dedicated to Sir James Edward Smith, which was reissued by his son in 1842.
He contributed two papers to the Linnean Society's Transactions, and left an extensive hortus siccus of algæ, as well as of flowering plants, together with fossils, music, and more than a thousand drawings of churches and other ancient buildings, executed by himself.