U. pumila x U. davidiana var. japonica
Hokkaido University Botanical Garden/University of Wisconsin-Madison
Sapporo Autumn Gold arose, as did the clone “Accolade”, from a spontaneous cross-pollination in a botanical garden. In this instance the parentage is Siberian elm and Japanese elm (a combination which was to much repeated in breeding programmes). The clone was cultivated by Eugene Smalley at the University of Wisconsin-Madison, and distributed by the US firm Pitney Bowes as part of its Elms Across Europe initiative in the early 1980s. As a result, Sapporo is the most frequently seen of modern hybrids. In this country it will often be found in a corner of a municipal park or cemetery where it is now semi mature.
Sapporo is commonly used as a highly resistant control clone in inoculation trials. In that capacity it was tested by the Italian breeding programme in 2000, scoring 2.78% and 1.22% for defoliation and dieback respectively. In accordance with its reputation, these scores are hard (but not impossible) to beat. It is said to be tolerant of verticillium wilt, but a stricken sapling seen in a Kentish nursery in 2011 suggested that there is no room for complacency.
Most specimens – and there are plenty to compare – tend to fork low down, and then to form a low, dome-shaped crown. The forking could be postponed by attentive management. Outwards arching main boughs will gradually lift the crown as the plant matures, but probably not to any great ultimate height. Early growth is vigorous. The mature bark is fairly impressive.
Sapporo has three significant faults. The first is that the foliage tends to clump, leaving many naked patches within the canopy. This is most marked on infertile soils or in conditions otherwise adverse, and can be seen in photographs brought up by a Google search. The second is that the tree has inherited one of the Siberian elm’s worst vices – the tendency for branches to die back for no apparent reason. The photograph to the right shows this in a tree which was recently pruned to remove dead wood; this dieback was presumably subsequent. The third, which in fact is not indisputably a fault, is the tree’s form. That is dealt with in the “assessment” section below.
Bright or mid-green and distinctively feathery, as the photograph shows. The pumila (Siberian elm) character is strong. Autumn colour is clear gold. There is none of the richness or informality of European elm foliage here, but the spectacle of a massed planting of Sapporo in early summer is striking, and some individual trees could be described (just about) as elegant.
Sapporo is tried and tested. Descriptions of the tree often take issue with its shape, suggesting that it is of no use in the open landscape. That doesn’t seem entirely fair. If well grown, Sapporo is not any more foreign in regard to shape than is the Huntingdon elm. The crown is not very weighty or cohesive in summer, but in winter and early spring it is capable of roofing a landscape in the way that only elm can. The main caution is not to plant Sapporo on anything but fertile, sheltered and well-watered ground. Elsewhere, it will gradually degenerate into a tree quite as unsatisfactory as its parent, the Siberian elm. But provided it is well situated and cared for, and preferably planted as one of a sensitively spaced group, it should not disappoint.