The garden covers an area of 16 hectares (40 acres). The site is almost entirely on level ground and in addition to its scientific value, the garden is highly rated by gardening enthusiasts. It holds a plant collection of over 8000 plant species from all over the world to facilitate teaching and research. The garden was created for the University of Cambridge in 1831 by Professor John Stevens Henslow (Charles Darwin's mentor) and was opened to the public in 1846. According to the garden's own statistics there were more than 200,000 visitors in 2011.
After several unsuccessful attempts during the 16th, 17th, and early 18th centuries, a University Botanic Garden was finally established at Cambridge between 1760 and 1763. This was not on the site of the present Garden, but in the centre of the town, on about 5 acres of land then occupied by 'The Mansion House' of the old Augustinian friary, and today by the New Museums Site and other university buildings. It was Dr. Richard Walker, Vice-Master of Trinity College, who, on the advice of Philip Miller of the Chelsea Physic Garden, purchased the property for £1,600, and presented it to the University for use as a Botanic Garden. For some years the Garden was known as the Walkerian Botanic Garden, and there is, at the present Garden, a Walkerian Society named in honour of its founder.
The Walkerian Garden was laid out and developed by the then professor of botany, Thomas Martyn. This small Garden was conceived as a typical Renaissance physic garden, inspired by the Chelsea Physic Garden in London. It grew herbaceous plants used in the teaching of medical students at the University. Glasshouses and a lecture room for the professor were built and the teaching of botany in Cambridge, which was then at a low ebb, received, for a time, a considerable stimulus. This improvement, however, did not last for long. Martyn left in 1798 and only visited Cambridge only occasionally until his death in 1825. About 1790 James Donn was appointed Curator and in 1796 he published the first edition of Hortus Cantabrigiensis, a list of the plants in the Garden which reached its 13th edition in 1845, long after Donn's death.
In 1825 John Stevens Henslow, Charles Darwin's teacher at Cambridge, succeeded Martyn as professor of botany and soon realized that a larger site, farther from the centre of Cambridge, was desirable for the Botanic Garden. In 1831 the University purchased the present site of about 40 acres to the south of the town on the Trumpington Road, and in 1846 the first tree was planted. It had been the intention to lay out the whole 40 acres as a Botanic Garden, but presumably funds were lacking, and in fact only 20 acres were planted, the remainder being let out as allotments.
The planning of the new Garden was carried out by Professor Henslow, assisted by young Cardale Babington. The land was flat and unpromising as a garden site, but the layout was planned with great skill, utilizing an old gravel pit to construct a lake with a high mound running into it. Trees and shrubs were planted according to their botanical sequence, a range of glasshouses was built in the 1860s, and a rock garden, one of the earliest of its kind in the country, was constructed about the same time. The Garden has also long been known for its many fine specimens of rare trees. By the 1870s the main features of the Garden had been developed and, it was ready to play its part in the great expansion of botanical teaching and research that was about to take place at Cambridge. During the early years of the 20th century much of the pioneer work of William Bateson, Charles Chamberlain Hurst, and Edith Rebecca Saunders on plant genetics was carried out at the Garden, and it was later used for researches on plant physiology by Frederick Blackman and George Edward Briggs, and on plant pathology by Frederick Tom Brooks and others.