Thomas Andrew Knight (1759–1838), FRS, of Elton Hall in the parish of Elton in Herefordshire (4 miles south-west of Ludlow) and later of Downton Castle (3 miles north-west of Elton), was a horticulturalist and botanist. He served as the 2nd President of the Royal Horticultural Society (1811–1838).
He was born at Wormesley Grange, five miles north-west of Hereford in Herefordshire, the second son of Rev. Thomas Knight (1697–1764) of Wormsley Grange, Rector of Bewdley, Worcestershire, by his wife Ursula Nash, a daughter of Frederick Nash of Dinham, Shropshire. He was the heir of his unmarried elder brother the art connoisseur Payne Knight (1750–1824), MP, who had been the heir not only of their father but also of their uncle Richard II Knight (1693–1765) of Croft Castle and of Downton, and who had re-built Downton Hall as the surviving Gothic revival style Downton Castle. Richard II Knight as the eldest of five sons was the heir of his father Richard I Knight (1659–1745), of Downton, a wealthy ironmaster of Bringewood Ironworks, on the Downton estate, who founded the family's great fortune.
He attended Balliol College, Oxford. After graduation, he took up the study of horticulture. Attention was first called to his work in 1795 by the publication of the results of his research into the propagation of fruit trees and the diseases prevalent among them. He used 10,000 acres (4,000 ha) of land he inherited to conduct breeding of plants including strawberries, cabbages and peas and built an extensive greenhouse. In 1797 he published his Treatise on the Culture of the Apple and Pear, and on the Manufacture of Cider and Perry, a work which passed through several editions. He was one of the leading students of horticulture in the eighteenth and nineteenth centuries, but his personal papers disappeared after his death.
Knight performed basic physiological experiments on plants, which work had been performed before only rarely. He elucidated the effects of gravity on seedlings and how decay in fruit trees was passed on by grafting. In many respects his work looked back to that of Rev. Stephen Hales. His goals were always strictly practical, aiming to improve useful food plants by breeding for better qualities. The Downton strawberry was the ancestor of most important modern strawberries until recent times.
It is not widely known that he studied variation in peas and found many of the same results as Mendel, but he failed to make the same imaginative leap about how these changes took place. Knight intentionally shut himself off from outside scientific influences. He refused to read anyone else's scientific papers until Sir Joseph Banks, with whom he had a voluminous correspondence, persuaded him to do so. Knight reported on all his work in the Transactions of the Royal Society of London.
From 1811 to 1838 Knight was president of the London Horticultural Society, founded in 1804. Banks, president of the Royal Society, had recognised Knight's striking contributions to science and prevailed upon him to join the Horticultural Society, as it was then known. After the death of the first president, George Legge, 3rd Earl of Dartmouth, Banks proposed Knight to be president. In 1864 the Society received a royal patent from Albert, Prince Consort, which permitted it to be known thenceforth as the Royal Horticultural Society. Banks called upon Knight to write a "prospectus" for the society (what would now be called a mission statement), outlining its functions and purpose.