Gertrude Jekyll VMH (/ˈdʒiːkəl/ JEE-kəl; 29 November 1843 – 8 December 1932) was a British horticulturist, garden designer, craftswoman, photographer, writer and artist. She created over 400 gardens in the United Kingdom, Europe and the United States, and wrote over 1000 articles for magazines such as Country Life and William Robinson's The Garden. Jekyll has been described as "a premier influence in garden design" by British and American gardening enthusiasts.

Jekyll was born at 2 Grafton Street, Mayfair, London, the fifth of the seven children of Captain Edward Joseph Hill Jekyll, Esquire, an officer in the Grenadier Guards, and his wife Julia, née Hammersley. In 1848 her family left London and moved to Bramley House in Surrey. Gertrude’s education was at home, but it included meeting various well-known figures such as Michael Faraday and Felix Mendelssohn. She started sketching and gardening at Bramley House, and in 1861 she went to the National School of Art, South Kensington. Her paintings were exhibited at the Royal Academy and the Society of Female Artists. In 1863, she went with Charles and Mary Newton to Greece and Turkey, which stimulated a life-long interest in Mediterranean plants.

Her siblings were also interested gardeners – her sister Caroline in Italy and her younger brother, Walter Jekyll, in Jamaica. Walter, sometime Minor Canon of Worcester Cathedral and Chaplain of Malta, was a friend of Robert Louis Stevenson, who borrowed the family name for his 1886 novella Strange Case of Dr Jekyll and Mr Hyde.

In 1868 the Jekylls moved again, this time to Wargrave Hill, Berkshire. The following year, she got to know William Morris, and was profoundly influenced by his idea of the unity of the arts. During the 1870s, she turned her hand to all sorts of arts and crafts, from embroidering tablecloths to smithing gates, and designing both interiors and gardens. She also continued to collect plants during trips to the Mediterranean.

In 1881, Jekyll started writing for William Robinson’s magazine, The Garden. Following her father’s death in 1876, Gertrude’s mother commissioned a house in Munstead Heath near Godalming from John James Stevenson, Gertrude herself designing the garden. Jekyll, who never married, lived with her mother until 1895, when she built a house over the way. This was Munstead Wood, designed by Edwin Lutyens, the first of their house-and-garden collaborations. She established a nursery here, from which she supplied her garden designs. In 1904, Jekyll returned to her childhood home in the village of Bramley to design a garden for Millmead House in Snowdenham Lane.

Jekyll continued to write for various gardening magazines and journals, and for Country Life, and she published her first book, Wood and Garden, in 1899. In 1908, she published her best-seller, Colour in the Flower Garden. Jekyll was also interested in traditional cottage furnishings and rural crafts, and concerned that they were disappearing. Her book Old West Surrey (1904) records many aspects of 19th-century country life, with over 300 photographs taken by Jekyll herself.

Jekyll was one half of one of the most influential and historical partnerships of the Arts and Crafts movement, thanks to her association with the English architect Edwin Lutyens, for whose projects she created numerous landscapes. (In 1900, Lutyens and Jekyll's brother Herbert designed the British Pavilion for the Paris Exposition.)

Jekyll is remembered for her outstanding designs and subtle, painterly approach to the arrangement of the gardens she created, particularly her "hardy flower borders". Her work is known for its radiant colour and the brush-like strokes of her plantings; it is suggested by some that the Impressionistic-style schemes may have been due to Jekyll's deteriorating eyesight, which largely put an end to her career as a painter and watercolourist. Her artistic ability had been evident when she was a child and she had trained as an artist, and she also collaborated with Minnie Walters Anson.