A short list of seeds they like to soak are peas, beans, pumpkins and other winter squash, chard, beets, sunflower, lupins, broad beans, and cucumbers. Most other medium to large vegetable and flower seeds with thick fur benefit from soaking. Other common garden seeds that appreciate soaking are basil, beet, chard, corn, and pumpkins. Some people also pre-soak tomato and pepper seeds.
The short answer is because your seeds were designed to be abused. Mother Nature is not kind to a little seed. In nature, a seed can expect to encounter severe heat and cold, very humid or dry conditions, and may even need to survive an animal's acid-filled digestive tract. In short, seeds have been developed over millions of years with defenses to survive terrible conditions.
But in your modern garden, a seed is relatively pampered. Soaking seeds before planting helps break down the seed's natural defenses against what you expect from Mother Nature, which then allows it to germinate faster. Large seeds, such as sunflowers and nasturtiums, benefit from soaking them in warm water overnight. Other flower seeds that will germinate faster are moonflowers, lupins, peas, and morning glories.
Place containers in a warm place, such as in the clothes dryer or on top of the refrigerator. Some seeds have external (exogenous) latency. Its hard, impermeable seed covers are inaccessible to water and oxygen without physical alteration. In nature, freezing temperatures or extreme heat from wildfires could split seed cover and promote germination.
Gardeners can try several methods to scarify or wear down the seed cover. If the seed covers are not extremely hard, it may be sufficient to soak the seeds in warm (not hot) water for up to 24 hours. Harder seeds may need to be soaked in vinegar overnight. Use white vinegar that contains at least 5% acetic acid and don't forget to rinse the seeds with water before sowing.
Never soak seeds for too long, as they can “drown” without oxygen. Soaking is beneficial for pea seeds, as well as other seeds with thick and hard coats. You can (and should) soak the beans (Vicia faba), beet, cucumber, corn and pumpkin seeds. Seeds have everything they need to become a plant, as long as they receive nutrients from soil, water and sunlight.
However, they must also come out of the hard shell in which they are locked. Soaking seeds in warm water helps soften the shell, allowing the germination process to be easier. I am often the first to admit that it doesn't take much if you want to start from seeds, just a good growing medium, sunlight and water. But if it's too cold or too wet, too hot, or too dry for that particular seed, it won't germinate at all.
It also relieves some of the stress of ensuring that the soil is sufficiently moist after you have sown a row of seeds, a task that is a little more complicated when planting seeds directly outside than when starting indoors. By pre-soaking (pre-soaking) the seeds in water ahead of time, you remove some of those barriers so that the seeds are ready to sprout when you stick them in the soil. For thick-skinned seeds, such as peas, try to put them for 8 to 10 hours (or all night, assuming you soak them just before bed and sow them first thing in the morning). You may have seen this in tomato seeds that seemed to have sprouted inside an overripe tomato, or in pumpkin seeds that suddenly germinated inside pumpkins that you left on the counter for too long.
Seeds can float because they lack viable embryos or nutrient stores, making them less dense than “good” seeds that sink into water. Soaking seeds before planting is an old gardener trick that many new gardeners are unaware of. Temperatures below or above have a significant impact on germination, either by slowing down the process or causing the seeds to break down completely. They soak for such a short period of time that it is not possible to know if they will germinate or not, sometimes they will.
Although you can soak these seeds, small, moist seeds are difficult to handle and tend to stick together. The benefit of soaking seeds before planting them is that germination time will be reduced, which means you can have happy plants and grow faster. Despite being cold-tolerant, pea seeds prefer to sprout during the day at soil temperatures of 60° F to 80° F. A safe place to start is a couple of hours; after that, check your seeds every hour until you start seeing them filled.
No matter what method you use to scarify your seeds, be careful not to damage the seed embryo and lose viability. Once the seeds soften a bit and begin to swell (an appearance you'll become familiar with the more often you soak the seeds), saw them in the ground immediately. . .