Insect pollination and artificial pollination can be used. Artificial pollination: when the male and female flowers are in full bloom, collect the pollen of the male flowers and apply it to the stigma of the female flowers with a brush, and apply it evenly. You can also take off the male flowers and remove the corolla, and apply the pollen directly to the stigma of the female flowers, preferably twice, and pollinate again in the afternoon to ensure success.