Walnut is a wind-pollinated flower. The pollen grains are medium-sized, about 43.2 microns × 54.6 microns in diameter, and can fly in the wind. According to European and American literature, the pollen of some walnut varieties has strong flying ability, and pollen can be collected up to 160 meters away from the tree. Observations from Hebei Agricultural University show that the amount and distance of walnut pollen scattered are related to wind speed. Within a certain distance, the amount of pollen scattered increases with the increase of wind speed; at a certain wind speed, the amount of pollen scattered decreases with the increase of distance. When there are no pollinating trees or the distance to the pollinating trees is more than 100 meters, artificial pollination should be supplemented. During artificial pollination, attention should be paid to maintaining the vitality of pollen. In its natural state, the lifespan of walnut pollen is only about 2 to 3 days; it can last for 3 to 5 days at room temperature. Walnut pollen is not resistant to low temperature and drying. The optimal storage temperature is 3°C and can be stored for more than 30 days. The greater the relative humidity, the slower the pollen viability decreases, so it is not suitable to store in dry conditions. When iron walnut pollen was stored at a constant temperature of 4°C for 45 days, 1.5% of the pollen still germinated.

Walnut female flowers have a single ovule. After pollen germination, only a few pollen tubes reach the ovule. Excessive pollen is neither necessary nor easy to cause the stigma to lose water, which is not conducive to pollen germination. The appropriate period for pollination is when the stigma is spread out like an eyebrow and mucus is secreted. Generally, only a few grains of pollen fall on the stigma will germinate. The germinated pollen tube encounters the intercellular space of papilla cells when it is elongating on the stigma surface and penetrates into it, and extends down along the intercellular space of the cells, directly to the top of the ovary chamber, into the ovary cavity, and along the surface of the integument. It extends subcutaneously to the top of the young septum, then penetrates the septum and grows to the chalazal area. At this time, the direction changes to grow upward, passing through the nucellus and reaching the embryo sac. Studies have shown that the distribution of calcium in the pistil is one of the reasons for inducing the directional growth of pollen tubes. The role of nutrient supply and structure is also obvious. There may also be an unclarified source of chemotropism. The time for the walnut pollen tube to reach the embryo sac from the stigma is about 4 days after pollination. Walnuts undergo double fertilization, that is, the pollen tube releases two sperms, which move toward the egg and the central nucleus respectively to complete the fertilization process.

Both walnuts and iron walnuts have certain parthenogenetic abilities. There are often solitary trees without pollination conditions that can bear fruit every year, and their nuts also have mature seed embryos. From 1962 to 1963, Hebei Agricultural University used pollen from heterogeneous plants to pollinate female walnut flowers, treated with IAA, NAA, 2,4-D, and bagged to isolate pollen. Fruits with seed embryos were obtained.