The ripening period of walnut fruits varies with different varieties and climatic conditions. The maturity period of early-maturing and late-maturing varieties (types) can differ by 10 to 25 days. Most of the varieties cultivated in northern production areas mature from early to mid-September; early-maturing varieties (types) mature as early as early August. The maturity period of the same variety in different regions is not the same. In the same area, plain areas mature earlier than mountainous areas, sunny slopes mature earlier than shady slopes, and drought years mature earlier than rainy years.

Walnuts need to be fully mature before they can be harvested. If harvested too early, the peel will be difficult to peel off, the kernels will not be full, the kernel yield and oil content will be low, the flavor will be poor, and the fruit cannot be stored. If harvested too late, the fruit will drop. If the fruit falls on the ground and is not picked up in time, it will easily cause mildew. . Therefore, timely harvesting is very important. Under normal circumstances, when walnut fruits mature, the color of the involucre (peel) changes from dark green or green to yellow-green or light yellow, with sparse hairs, cracks appear on the top of some fruits, the green peel is easy to peel off, the kernels are thick, the young embryos are mature, and the flavor fragrant. The morphological characteristics of walnut fruits are reliable as indicators of fruit maturity.