Castanopsis sieboldii - Growing Guide

Two extremely rare species of Castanopsis have grown at Caerhays for nearly a hundred years. C. concolor and C. cuspidata were both collected by George Forrest in Yunnan. They are slow growing small evergreen trees with densely packed leaves and one could easily pass them by here in the garden without beginning to notice them.

Castanopsis are allied to Quercus and Castanea and it is only when they produce fruit that you can appreciate what a distinct genus they represent. One might readily try to identify them as evergreen oaks until they grow large enough to fruit.

The fruits or nuts are entirely enclosed in a sweet chestnut-like capsule with prickles. As in some species of oak the enclosed nuts take two years to ripen. The male flowers are upright and, on our young plant of C. concolor, the fruits have so far failed to mature. C. cuspidata fruits only occasionally but we have occasionally managed to show it at autumn Garden Society events.

Castanopsis sieboldii has been planted out here for the last five years and is making good headway. It is now nearly 6ft tall in a sheltered spot. We sourced some small seedlings from a French seedsman and are now able to offer a very few plants of this real rarity. C. sieboldii has larger leaves than the other two species growing here already. They are more ovate and with more crinkled edges.

Otherwise I can find virtually nothing in any of the reference books about C. sieboldii so we will have to wait and see how it performs. There are apparently over 100 species of Castanopsis in SE Asia so there is much research to do.

Castanopsis grow well here in full shelter and with dappled shade. Full sun and exposure are far too great a risk with such rarities.