Unlike its elder stablemate 'Sapporo Autumn Gold', 'New Horizon' initially has a compact, pyramidal form, with comparatively dense foliage comprising glabrous, dark-green, elliptical leaves < 12 cm long by 7 cm broad, occasionally without the asymmetric bases typical of the genus. The perfect, apetalous wind-pollinated flowers appear in March, followed by the seeds in April; flowering, and consequent fruiting, is sparse, in common with its female parent Japanese Elm, and usually begins when the tree is aged 8 years. The tree's growth habit is unusual; in an assessment at U C Davis as part of the National Elm Trial, its stem diameter increased faster than any other of the 15 cultivars, but increase in height, averaging 0.9 m per annum, made it one of the slowest growing, vertically. In commerce in the US, the tree is occasionally propagated by grafting onto an Ulmus pumila rootstock, rather than simply rooting cuttings as normally practiced in North America and Europe.
The tree has not been an unqualified success. In the elm trials conducted by the University of Minnesota, 'New Horizon' was found to need relatively high levels of maintenance, largely owing to its predilection for co-dominant leaders and heavy side branches. In the Netherlands, removal of sideshoots from the lower trunk was found to be necessary twice a year. In trials in eastern Arizona it often exhibited > 25% crown dieback over winter and a very high level of leaf scorch in summer. The tree is currently being evaluated in the National Elm Trial coordinated by Colorado State University. 'New Horizon' was introduced to Europe by the Conrad Appel nursery in Darmstadt, Germany, which propagated the tree under licence as one of the hybrid elms offered in the Resista series ; the tree is currently propagated by Eisele GmbH. The tree was introduced to the UK and Ireland by Hillier Nurseries, who have sole distribution rights. 'New Horizon' was named 'Best New Plant Variety' by Horticulture Week in 2005, however, an assessment by Butterfly Conservation found its growth on heavy, poorly drained ground negligible. Nevertheless, the tree has tolerated flooding, by both freshwater in England, and seawater along the Baltic coast in Germany . Trees at exposed sites in Hampshire exhibited much the same degree of dieback experienced in the Arizona trials despite the extreme differences in climate. However no losses have been sustained, and in sheltered conditions on deep loam over chalk, 'New Horizon' grew healthily if relatively slowly, increasing in height by approximately 50 cm per annum, less than half the speed of the Dutch hybrids such as 'Dodoens' planted with it. The trees in the English trials first flowered aged 10 years, in late March. In 2004, 80 trees were donated to the Greater London Council as part of the grower's European Elm City promotion; similar gifts were also made to Belfast, Cardiff, and Hamburg. In 2010, 100 trees were planted in the London borough of Enfield to aid and abet the conservation of the White-letter Hairstreak Satyrium w-album. Another hundred were included in the tree planting at the Olympic Park. Forty have been planted in Richmond Park, near the Dysart gate.
Conservation
'New Horizon' was found hosting the endangered White-letter Hairstreak at the Vauxhall Pleasure Gardens, London, in 2017; this is the first recorded instance of the butterfly breeding on the cultivar in the UK.
Accessions
North America
Bickelhaupt Arboretum, US. Acc. no. 01-008
Chicago Botanic Garden, US. 3 trees, no other details available.
Morton Arboretum, US. Acc. no. 271-2008.
Europe
Arboretum de la Petite Loiterie , Monthodon, France. No details available.
Botanischer Garten Marburg , Marburg, Germany. No details available.
Brighton & Hove City Council, UK. NCCPG Elm Collection. Planted frequently as a street tree.
Great Fontley Farm, Fareham, UK. Butterfly Conservation elm trials plantation, one standard planted 2007.
Royal Horticultural Society Gardens, Wisley, UK. No details available.
Sir Harold Hillier Gardens, Romsey, UK. Acc. no. 2004.0177
