There are two reasons. First, there are its own factors: 1. Seed maturity affects its germination rate; 2. Seed life, if the seeds with short life are stored for too long, the germination rate will gradually decrease; 3. When seeds are dormant, the germination rate is low, and with the decrease of dormancy, the germination rate gradually increases; Second external environment: 1. Temperature, when the environmental temperature of the seeds is beyond the temperature range required for germination (low temperature or high temperature), the germination rate of the seeds will be obviously reduced or not germinated; 2. Humidity, humidity is one of the important factors affecting seed germination, and too much or too little humidity is not conducive to seed germination; 3. Light, some seeds are light-demanding seeds and generally do not grow in dark environment.