Ulmus New Horizon elm trees growing in rows in field

Resista® Elms Development

In the 1970s and early 1980s, many millions of Elms succumbed to a new virulent strain of Dutch Elm Disease, drastically changing the landscape throughout the British Isles and Europe.

This terrible disease had already caused significant Elm deaths in America. As a result, the scientist Professor Smalley was already working on a breeding programme in the 1950s to find a resistant elm at the University of Wisconsin. He crossed two elms, Ulmus japonica and Ulmus pumila. The resultant seedlings, when they were large enough, were injected with the fungus that caused Dutch Elm Disease. Most seedlings died, but a few showed resistance and survived. These were re-crossed to strengthen the resistance and tested again. Further selection was made for form, leaf colour, vigour and hardiness. Ultimately, this programme led to a range of Elms known as Resista® Elms.

There are now half a dozen varieties available for planting in Europe, and Hillier Nurseries are the exclusive partner for the UK and Ireland. The first of these are Ulmus ‘New Horizon’ and Ulmus ‘Rebona’. Both grow on their own roots as they are propagated from cuttings. While they are on the nursery, they are micro-chipped so they are all traceable. This is important to protect the decades of research, the rights of the growers and should any problems arise, their provenance can be traced.

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Long-term Success for Elms

Ulmus ‘New Horizon’ was formally launched by Hillier back in 2005 at RHS Chelsea Flower Show. This was the same year that the Elm was awarded Best New Plant at the  Grower of the Year Awards. Tens of thousands of these new resistant Elms have now been planted the length and breadth of the British Isles and in Europe — from Madrid  to the Steppes of Russia – with no incident of any succumbing to Dutch Elm Disease.

A further positive outcome has been the ability of the elms to become a habitat for the endangered White-letter Hairstreak butterfly that relies on the Elm trees to breed. This once common butterfly experienced a catastrophic decline in population in line with the demise of the native Elm.

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Ulmus New Horizon elm trees on street


Both Ulmus ‘New Horizon’ and Ulmus ‘Rebona’ share the following characteristics:

• 100% Resistant to Dutch Elm Disease
• Tolerant of pollution
• Tolerant of salt (making them first class coastal trees)
• Tolerant of drought
• Tolerant of short-term waterlogging
• Very quick establishment
• Fast growing
• Tolerant of weather extremes – hot and cold temperatures
• Great for insects, in particular the endangered Whiteletter Hairstreak butterfly

The two hybrids differ in their form. Ulmus ‘New Horizon’ broadens to become a large tree with a rounded canopy. Ulmus ‘Rebona’ also becomes a large tree, but with a broadly columnar habit. Rigorous trials are currently underway for further disease resistant Elm varieties.

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Ulmus New Horizon elm trees in avenue

Key Trees

Ulmus ‘New Horizon’

Ulmus New Horizon is a medium to large tree that shows complete resistance to Dutch Elm …

Ulmus ‘Rebona’

Ulmus ‘Rebona’ is a hybrid originating from a Japanese clone of Ulmus japonica and Ulmus pumila, …

Ulmus ‘Fiorente’

Ulmus ‘Fiorente’ commonly known as Fiorente Elm, is a strikingly beautiful tree. The name of the …

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