Why Vegetable and Grain Seeds Are Soaked Before Sowing, and the Specific Methods
Soaking seeds of vegetables and grains means soaking vegetable and grain seeds in clean water or various solutions.
The purpose of soaking seeds is to let the seed grains absorb water faster and reach the moisture content needed for normal germination. The moisture content of dry seeds is usually below 15%, their physiological activity is very weak, and they are in a dormant state. After the seeds absorb water, the seed coat swells and softens, the oxygen dissolved in the water enters the cells along with the water, and the enzymes in the seeds begin to activate. Through the action of the enzymes, the respiration of the embryo increases, and the insoluble substances stored in the endosperm gradually turn into soluble substances and are transported to the embryo along with the water. Once the seed embryo has obtained water, energy and nutrients, the cells begin to divide and elongate under suitable temperature and oxygen conditions, breaking through the glume (germination). It can be seen that for a seed to germinate, it must first absorb enough water. However, a seed does not germinate just because there is water; it must absorb at least the equivalent of 15—18% of its own weight in water before it can begin to germinate. Only when the water absorbed reaches 40% of its own weight can it germinate normally.
The time required for soaking seeds is related to the thickness of the seed hull, the strength of permeability, the moisture content of the seeds before soaking, and the water temperature used for soaking. Indica rice absorbs water faster, while japonica rice absorbs water more slowly; seeds with low moisture content absorb water faster, while those with high moisture content absorb it more slowly; higher temperatures are faster, and lower temperatures are slower. Whether the seeds have absorbed enough water can be judged by their appearance. Seeds that have absorbed enough water appear semi-transparent, the embryo and endosperm can be vaguely distinguished through the hull, the embryo swells and protrudes, the endosperm becomes soft, and after peeling off the hull the rice grain can be crushed by hand, with no cracking sound when broken.
Soaking vegetable seeds before sowing allows the seeds to absorb enough water in a short time and sprout quickly, and it can also sterilize and prevent disease and enhance the resistance of the seeds. Here are four common methods of soaking vegetable seeds before sowing: hot water soaking, warm water soaking, warm soup soaking, and sodium hydroxide soaking.
1. Hot water soaking method
This helps kill pathogens and insect eggs on the seed surface. The water temperature is required to be 75°C-85°C, and the amount of water used is about 4-5 times that of the seeds. Stir while soaking until the water temperature drops to 30°C and the seeds are fully swollen. This method is suitable for seeds with hard, thick seed coats that are difficult for water to penetrate, such as Chinese chives, loofah, and winter melon.
2. Warm water soaking method
The water temperature is required to be 20°C-30°C, and it is suitable for seeds with thin seed coats that absorb water quickly, such as Chinese cabbage and cabbage. Soak until the seeds have no hard core.
3. Warm soup soaking method
This method is fairly effective in preventing tomato early blight, eggplant brown spot disease, sweet pepper anthracnose, cucumber angular leaf spot, celery late blight, and so on. The water temperature and time must be accurate, and after soaking for a sufficient time the seeds must be cooled immediately. For example, the soaking water temperature for tomato is 52°C, and the soaking time is 30min; the soaking water temperature for sweet pepper, cucumber, and eggplant is 55°C, and the soaking time is 12h; the soaking water temperature for celery is 48°C, and the soaking time is 30min.
4. Sodium hydroxide soaking method
This method can kill most viruses and fungi inside and outside the vegetable seeds, and can effectively prevent vegetable viral diseases, anthracnose, angular leaf spot, and early blight, among others. First soak the vegetable seeds in clean water for 4h, then place them in a 25% sodium hydroxide solution for 15min, and finally rinse with clean water and air-dry for 18h.