Ulmus parvofolia, or chinese elm, is a species of elm natively found in Japan, China and Vietnam. It is a species often found in bonsai culture because of the fine leaves and very refined growth. It is easily obtained as many of the larger hardware chains and supermarkets carry this species as an ‘indoor bonsai’ often offering dozens of perfectly identical mass produced mallsai, originating from growing fields in China.
Not to mix up with Zelkova serrata. Zelkova’s are very similar to Ulmus in all aspects. The main differences lays in the shape of their fruit (Often nog very helpfull when growinng bonsai) and the serration of the leaves: Ulmus has leaves with two levels of serration, and Zelkova only one.
Position your elm in a bright light spot. The plant is fully hardy and can remain outside in winter, even when strong frost is expected. Just make sure the roots are well-protected. Do not put a recently bought elm directly in the winter-cold. In order to be frost-hardy elms need -just like any other tree- to spent the fall outside, in order to harden off.
Watering. Ulmus needs to be watered regularly, but when needed. So never let the soil dry out completely, but water only when the topsoil has started to dry out. Soggy soil may lead to root-rot and dying of the plant. Once the plant is in leaf, in spring through to the end of autum, add fertilizer to the water once every one to two weeks. Consider using a fertilizer with extra nitrogen during the first weeks of spring.
Trimming is key to a nice elm. These plants can grow very fine branches when trimmed properly. For refining of the tree, let branches grow 4-6 leaves before trimming back to 2 leaves. (If you trim earlier, the branch may die off; Pruning later may cause the branch to get too thick). Removal of thicker branches should be carried out in late summer or early fall.
repotting of ulmus is done as with most deciduous species in early spring, as the buds start to swell. As this is a fast growing species, in most cases annual rot pruning is required.