Knoll Gardens - Specialist Grower of Grasses and Perennials

Join us in our campaign to re-establish the
elm across the British Isles

Since the 1970s over 20 million elms have been lost to the ravages of Dutch Elm Disease in the UK alone. This huge loss has caused a dramatic change to our landscape as well as removing the natural habitat of many organisms.

Knoll Gardens is actively working to restore this lost heritage.

Vigorous foliage of young Princeton elm

Why are elms grown on their own roots superior? Knoll’s Princeton elms are all grown from cuttings on their own rootstock for a very good reason.
Dutch Elm Disease can be passed from tree-to-tree via intertwined roots. These are just as susceptible to the fungus as the tops of the trees. A beetle carrying the fungus can infect one tree and before long a whole area of elms could be decimated via root-to-root transmission. Until recently, it was only possible to reliably produce elms by grafting their cuttings onto seedling elm rootstock that had no resistance to DED. As the trees were then still vulnerable to disease some growers began grafting onto Siberian elm, (Ulmus pumila) rootstock. This presented different problems. Described by noted horticultural writer Dr Michael Dirr as 'one of, if not the, world’s worst trees', the greater concern with using this rootstock is one of long term incompatibility. For a large elm such as Princeton to have the roots of a tree that attains only half its average mature size can only result in an inadequate root system, albeit one that
may not become fully evident for decades to come.		Lord Montagu plants Princeton at Beaulieu
In the Princeton elm these problems have been overcome using new rooting technology. We are now producing own-root Princeton elms for the first time ensuring that all our disease tolerant elms really are 'Princeton from top to bottom'.
		Since most who plant large trees do so with the hopes that the tree may live for centuries to come, elms grown on their own root represent our best hope for the future. Published results from a recently concluded, 20 year research study conducted by Ohio State University, show that trees grown from cuttings on their own root average 56% greater caliper and canopy volume than trees grafted onto seedling rootstock.
elm rooted liner

		We are the sole UK supplier of the incredibly disease tolerant Princeton elm, Ulmus americana ‘Princeton’, a fast–growing tree with a classic elm shape and large leathery leaves. In its native USA 80 year old Princeton elms remain in perfect condition. It is this combination of disease tolerance and proven longevity that makes the Princeton elm unique and so well suited to our cause.
Young Princeton establishing in the UK. Photo courtesy of Butterfly Conservation

How you can help……….plant an elm for future generations Princeton elms are the perfect selection for gardens, arboreta, parks, estates and street plantings: anywhere a large, graceful and long-lived specimen tree would enhance the beauty of the landscape is the perfect spot for a Princeton elm! Shipped from the USA in winter, while dormant, barerooted elms are best planted during the winter period, though containerized trees can be planted at any time of year if watered sufficiently. For current availability, sizes and pricing please go to our online store or call us on 01202 873931.
		Roy Lancaster plants first tree in UK soil at Knoll Gardens

The country unites to re-establish the elm
In 2008 hundreds of trees arrived by ship and plane for despatch across the country. Thousands have now been planted across Britain. They have been planted by The Prince of Wales, Lord Montagu and Sir Elton John, supplied to the National Trust and the Royal Horticultural Society Gardens at Wisley, and delivered to locations as diverse as Rugby School and Morden village hall.
Roy Lancaster planted the UK’s first Princeton elm at Knoll Gardens back in 2003. Now the trees are being bought by individuals, landowners and government organisations, all uniting to help re-establish the elm across the country.

he Prince of Wales and The Duchess of Cornwall plant the disease tolerant Princeton Elm at Highgrove.

The Prince of Wales and The Duchess of Cornwall plant the disease tolerant Princeton Elm
(Ulmus americana ‘Princeton’) at Highgrove with The Column Bird ‘eye-catcher’ in the background.

The science behind our success
The Princeton elm was originally selected in 1920 for its superior horticultural and ornamental features including large leathery foliage, classic elm shape and observed resistance to known disease. Roads lined with Princeton elms planted in 1932 remain in perfect and picturesque condition today with a survival rate of over 95% from all causes. Considering the fact that all of the surrounding streets in the borough of Princeton planted with seedling American elms and presumably other elm varieties were virtually wiped out by Dutch elm disease, the vigorous survival of these Princeton elms is nothing short of remarkable.

Field production of young ‘Princetons in the USA

Tried and tested
In the early 1990's, the USDA National Arboretum tested several selected varieties, seedlings and hybrids of elms by injecting them with artificially severe doses of the most aggressive strain of Dutch elm disease. The Princeton elm had a 96% survival rate. No other variety of DED susceptible, large-leafed elm can boast this combination of disease resistance and longevity in the landscape.