Walnut trees fall with green stripes.

The top of the walnut tree is called the walnut flower.

Walnut ripens around the Millennium solar term every year. When the green peel outside the ripe pit bursts, the walnuts inside will automatically fall off.

In order to prevent walnuts from falling off on their own, people usually knock them down a few days in advance. Some nuts that have not been knocked out for a long time will be moldy when they get wet in the rain, which will lead to topping and being blown off by the wind.

Black walnut is a common North American tree. This used to be a very ordinary old forest. Now black walnut is rare and mouth-watering, and it is mainly used for high-quality woodworking.

Trees like shade (intolerance), and the best growth occurs in sunny open areas and moist fertile soil, which is common on the banks of their original habitats. The substances produced by black walnut are toxic or "allelopathic" to other plants called juglone.