Rice seeds require adequate temperature, moisture, and air (although they can germinate with insufficient air, they will not be robust). Below 10°C, rice seeds will not germinate. They start to germinate at temperatures between 11°C and 12°C, and germination is fastest between 25°C and 35°C.
If the temperature is insufficient, even if the rice seeds are sown, they will not germinate, or if they do, the process is very slow. If germination is delayed, several disadvantages arise: on one hand, the nutritional substances stored in the seeds gradually deplete, leading to weaker sprouts; on the other hand, seeds exposed to the elements for an extended period are susceptible to the effects of sun, dew, wind, and rain, which can cause them to scatter. Furthermore, they may be preyed upon by birds and animals, which can eat the seeds. Therefore, sowing seeds without pre-germination, aiming for uniform and rapid emergence, minimal loss, robust seedlings, and timely planting, is difficult to achieve.
Pre-germination is about taking control of the rice seeds in human hands. By providing appropriate temperature, moisture, and air, and carefully monitoring them day and night, you can ensure optimal conditions. Especially by providing the ideal temperature, the seeds can germinate quickly. Therefore, the sprouts are uniform and robust and are not subjected to natural disasters. Pre-germinated seeds sown on a sunny day quickly establish roots and sprout leaves once in the soil. Once the roots are firm and leaves have emerged, the seedlings are less vulnerable to being damaged or dislodged by wind and rain. For early rice or rice sown in cold regions, where the temperature is low and conditions are poor, seedlings grow slowly, and seeds sown directly in the field are highly susceptible to rotting or lodging, thus pre-germination is practiced. This is also done for medium-season rice.
Another significant benefit of pre-germination is that it can shorten the growing period, allowing rice to be planted in time in cold regions, enabling early planting and harvesting of double-season early rice, and early maturation of later-season rice. When the soil temperature is not yet suitable for sowing, pre-germinating the rice seeds and then immediately sowing them when conditions improve allows the rice sprouts to grow quickly. Pre-germination is a way to compete with nature for time and food.
However, there are exceptions. For example, for late rice varieties like “fall dry grain,” pre-germination is unnecessary. This is because the sowing time for late rice is later in the season when temperatures are already high, and the seeds can germinate quickly once in the soil without the need for artificial heating. Also, for safety, some choose to soak the seeds until they crack and show white before sowing.