The male flowers are inconspicuous yellow-green catkins produced in spring at the same time as the new leaves appear.

The heartnut is a sweet nut without a bitter aftertaste often intrinsic with black and Persian walnuts.

The very bold, decorative leaves and catkins produced in spring make it a common ornamental tree for planting in parks and large gardens.

Unlike the closely related and very similar North American butternut, Japanese walnut is resistant to the canker disease caused by the fungus Sirococcus clavigignenti-juglandacearum.

The two species hybridise readily; the resulting hybrid Juglans x bixbyi (otherwise known as J. cinerea x ailantifolia or 'buartnut') is also resistant to canker and is likewise planted as a replacement for butternuts.