New Horizon (elm hybrid)

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Ulmus New Horizon
Hybrid parentage
U. pumila x U. davidiana var. japonica
Cultivar
New Horizon
Origin
WARF, Wisconsin, USA

An American cultivar raised by the Wisconsin Alumni Research Foundation (WARF), New Horizon was derived from a crossing of Siberian Elm U.pumila with Japanese Elm U. davidiana var. japonica. Unlike an earlier crossing of the same species Sapporo Autumn Gold, the tree has a compact vase-shaped form, with comparatively dense foliage comprising elliptical leaves <10 cm long. Another sibling, Cathedral, has larger leaves almost identical to those of its male parent, the Japanese Elm, but is less resistant to disease.

New Horizon was patented in 1995, and is now also grown under licence by the Conrad Appel nursery in Darmstadt, Germany, where it forms one of the four hybrid elms in the Resista series. It has become a popular choice as a street tree courtesy of its high resistance to disease and compact habit. 80 trees were donated to the Greater London Council as part of the grower's European Elm City promotion in 2004; similar gifts were also made to Belfast and Hamburg.

The tree has not been an unqualified success however. In trials in eastern Arizona [1] it often exhibited > 25 % crown dieback over winter and a very high level of leaf scorch in summer. In trials in England by Butterfly Conservation, its growth on heavy, poorly-drained ground was negligible and it also exhibited much the same degree of dieback experienced in the Arizona trials. However, in very sheltered conditions on deep loam over chalk it grew strongly, increasing in height by over 50 cm per annum. The tree first flowered aged 10 years, in late March.

[edit] References

• Brookes, A. H. (2006). An evaluation of disease-resistant hybrid and exotic elms as larval host plants for the White-letter Hairstreak, Satyrium w-album. Part 1. Butterfly Conservation, Lulworth, England.