Conservation and biodiversity

As the destruction of natural habitats continues at a frightening rate, with a horrific number of plant extinctions each year, the Gardens have a significant role to play in conservation and biodiversity.

We are supporting Hampshire County Council’s conservation strategy by safeguarding irreplaceable assets and raising environmental awareness. Besides growing many plants rare in cultivation, we grow over 200 threatened plant species. We have supported a variety of conservation projects, including collaboration on biodiversity projects on a local, national and international level.

It is not only plants in their native habitats that need conserving. Many garden plants are becoming rare in cultivation. Superseded by more recent selections, or neglected for various reasons, it is difficult to say how many introductions have been reduced to just a few specimens in the country.

Conservation has always been an aim of Sir Harold Hillier Gardens. Our patron, Roy Lancaster, made this statement in 1978 on the importance of the Gardens for future generations:

One of the most important roles of the arboretum is the conservation of species. Certain plants and trees are threatened with extinction through various natural and human causes such as drought, fire, development and drainage schemes. One of the best means of helping the survival of threatened species is to grow them here. By doing this we can ensure that, if called upon, seeds, cuttings or plants are available for distribution where the need arises.

This statement still stands today and reflects the ever more evolving environmental challenges we face today and in the future.

Find out about Hampshire County Council Climate Change Strategy and Climate Change targets.

Member of staff in a tree

Our Champion Trees 

Although the Gardens and collection are relatively young, started in 1953, more than 600 of our trees are registered as Champions with the Tree Register of the British Isles TROBI, more than any other garden. Champion Trees are the largest, or only known specimens in the country, some of our trees are in the latter category 

Here’s a few highlights from the collection: 


The Harold Hillier herbarium in Jermyn’s House was founded in 1995 and officially opened by Dr Nigel Taylor, Curator of the Royal Botanic Gardens, Kew. It is a home for specimens collected by the late Sir Harold on his travels and it also houses specimens of plants growing in the Gardens, both native and introduced, particularly from our National Collections. It is also the official repository of the International Oak Society. Herbarium work is mainly carried out by the Gardens' volunteers. The herbarium contains over 8,000 specimens, both native and introduced and is open for research purposes by appointment.


Some 25 species of butterfly have been recorded within Sir Harold Hillier Gardens. This haven for butterflies is due to the availability of nectar from a wide range of native and non-native cultivated plants, the wildflower meadows, and close proximity to butterfly rich woodland.  

The season starts with the garden offering nectar sources to butterflies which hibernate as adults, including Brimstone, Small Tortoiseshell and Peacock. Following on are the species which spend winter as a chrysalis, such as the Orange Tip and the Greenveined White. By July, Meadow Browns, Ringlets, Marbled Whites and Gatekeepers, which spend winter as caterpillars, can be seen in the meadows. The rarest butterfly in the Gardens is the White-letter Hairstreak, and butterflies passing through from the Woods of the World include the Silver-washed Fritillary and the White Admiral.