[3] He was a corresponding member of the Caledonian Horticultural Society in Edinburgh and read a paper there in March 1814 entitled On the prevention of the blight in fruit trees.
[4] He had struck up a friendship with Thomas Gibbs of Ampthill in Bedfordshire, who was seedsman to the Board of Agriculture and had premises in Half Moon Street Piccadilly and a nursery in Brompton.
Some of his letters refer to the experiments that he was conducting at Woburn Abbey under the guidance of Sir Humphry Davy to compare the performance of different species and various mixtures of grasses and herbs on different types of soil.
[5] Sinclair had also consulted James Sowerby about the analysis of soils and submitted an advance copy of his publication on grasses to the 3rd Earl of Hardwicke for his opinion.
In 1822 the Duke of Bedford had begun a comprehensive collection of exotic and indigenous heaths as a way of recuperating from a very severe illness.
In his Introduction to Hortus ericaeus Woburnensis which was published in February 1825[10] the Duke states that the collection was completed under the superintendence of his former gardener, George Sinclair.
He also collected calcareous soils from around Luton and Dunstable and experimented in mixing them with various proportions of peat and ashes to try to find a potting medium suitable for the more exotic specimens of heaths.
[18] In 1830 the Duke of Bedford built a new flower market at Covent Garden, and Sinclair took up a tenancy with his partner, John Cormack, in one of the conservatories there.
In his obituary, written by J.C. Loudon in the Gardener's Magazine,[21] Sinclair's Hortus gramineus … is described as the most important work of its kind ever published; he "will hold a conspicuous station in all future times, as the introducer of a new and improved system of laying down lands in grass."
More recently, in January 2002 environmental scientists Andy Hector and Rowan Hooper wrote a paper entitled Darwin and the First Ecological Experiment.
[23] In On the Origin of Species[24] Darwin wrote, "It has been experimentally proved that if a plot of ground be sown with one species of grass, and a similar plot be sown with several distinct genera of grasses, a greater number of plants and a greater weight of dry herbage can thus be raised."
Despite some limitations Hector and Hooper described the experiments as impressive even by today's standards and believe that they influenced the development of Darwin's "principle of divergence" which preceded his theory of evolution by natural selection.