Hooey! It’s a bunch of hooey! Sweet pea seed that gets sown this time of year for next spring does NOT need to be soaked before sowing. In fact, unless there is some strange species of plant that has become that dependent on human intervention, NO seed need to be soaked prior to sowing. Not only is the technique completely unnecessary, but it is completely unnatural as well.
Think of it. In the wild, plants grow, bloom and produce seed. This seed does what it can to disperse and get into or onto the soil to germinate and grow into new plants to repeat the process. Some seed appeal to squirrels for burial. Some prefer to be partly digested by animals who eat their tasty fruit. Heck, some are reluctant to germinate until heated by a cleansing forest fire.
Plants employ quite a range of techniques to disperse their seed and promote germination. As strange as some of these techniques seem to us, they are all justified. They all exploit processes of the respective ecosystems they naturally inhabit. For example, seed that crave heat know that the fire that provides such heat also incinerates competing plants, leaving them vacant soil.
Regardless, there are NO plants that produce seed with an expectation that anyone will collect and soak them. Dry seed that need to rehydrate can and actually prefer to collect the moisture they need from the moist soil in which they grow. If the soil is too dry for them to rehydrate, they do not waste effort trying. They merely assume that they should wait for rainier weather.
Furthermore, seed that are needlessly soaked prior to sowing must be sown shortly after rehydrating. Unlike dry seed, rehydrated seed can not be returned to their original packet and stored for later.