The Hortus botanicus Leiden was founded by Leiden University in 1590, on the site of the current Front Garden. The first planting dates from 1594. The Hortus was continuously expanded in the course of the following centuries and the planting has undergone many changes, but many of the trees that were planted during the past 400 years can still be admired today. The most recent expansion involves the Chinese herbgarden. The buildings in the Hortus vary from the classical Orangery (1744) to the large glasshouse complex: the tropical glasshouses (1938) and the Winter Garden (2000).
In 1587 the young University of Leiden asked for permission from the mayor of Leiden to establish a hortus academicus behind the university building, for the benefit of the medical students. The request was granted in 1590, and the famous botanist Carolus Clusius (1526–1609) was appointed as prefect. Clusius arrived in Leiden in 1593. His knowledge, reputation, and international contacts allowed him to set up a very extensive plant collection. Clusius also urged the Dutch East India Company (VOC) to collect plants and (dried) plant specimens in the colonies. The original garden set up by Clusius was small (about 35 by 40 meters), but contained more than 1000 different plants.
The collecting of tropical (from the Indies) and sub-tropical (from the Cape Colony) plants was continued under Clusius' successors. Especially Herman Boerhaave (1668–1738, prefect from 1709–1730), contributed greatly to the fame of the Hortus with his efforts to collect new plants and specimens, and with his publications, such as a catalog of the plants then to be found in the Hortus.
Another major contribution to the collections was made by Philipp Franz von Siebold, a German physician who was employed on Deshima (Japan) by the VOC from 1823 until his expulsion by Japan in 1829. During that period he collected many dried and living plants from all over Japan (as well as animals, ethnographical objects, maps, etc.), and sent them to Leiden.
The first greenhouses appeared in the Hortus in the second half of the 17th century, the monumental Orangery was built between 1740 and 1744. From its original plan the Hortus was expanded in 1736 by Adriaan van Royen and Carl Linnaeus, and in 1817 by Theodor Friedrich Ludwig Nees von Esenbeck and Sebald Justinus Brugmans. In 1857, a part was used for building the new Leiden Observatory