Curtis, a Quaker, was eager to share his horticultural knowledge with others; when a projected course of lectures at Chelsea did not materialize, he arranged one of his own, on botany and horticulture, in the new garden which he had made for himself in "Lambeth Marsh".  Here he also cultivated some six thousand species of plants. But his prime interest was in the British flora, especially in such flowers as grew in the neighborhood of London. With the support of Lord Bute, he embarked on his first ambitious project, the Flora Londinensis — a series of coloured folio illustrations and descriptions of the plants which grew within a radius of ten miles of the metropolis.

The first part of Flora Londinensis appeared in 1777, and in the same year Curtis, overburdened with work, resigned his post at Chelsea. For ten years he continued perseveringly at his congenial but unremenerative task; by 1787, the results of his labours were two splendid folio volumes and a deficit which made the continuance of his venture impossible. He understood the cause of the trouble and saw the remedy: if his clients refused to buy folio pictures of the unassuming plants that grew by the wayside, he would win their patronage with octavo engravings of the bright exotics with filled their gardens. Thus, in 1787, the Botanical Magazine was born. As Curtis himself said, it brought him "pudding" whereas Flora Londinensis had only brought him praise.