Fast-growing sturdy tree, a hybrid between A. japonica and A. subcordata. Initially, the branches grow straight up, later bending horizontally. Young branches are grey-green and older branches turn brown-green and have many lenticels. The leaf buds are on small stalks. The scattered, sharply serrated and dark green leaves grow to about 15 cm and unfurl purplish. It is oblong to ovate, appears early in spring and stays on the tree for a long time. The first brown-yellow catkins often appear as early as the end of January. Grows on all types of soil and is very hardy. Has no problems with (sea) wind. Alnus spaethii is a highly valued and frequently used alder found by Ludwig Späth in the Späth Arboretum near the Späth Baumschulen in Berlin.
Alnus ×spaethii 'Spaeth' is gyorsan növő and can eventually reach a height of , depending on the site and climate conditions.
The right time to plant Alnus ×spaethii 'Spaeth' is during the dormancy period. In Western Europe, Alnus ×spaethii 'Spaeth' with root balls can generally be planted from mid-November to late April, although this depends strongly on the climatic conditions and the species of tree.