Freezing generally retains nutrients well for a few months, but many of the microbial benefits are negatively effected.

That said, seaweed teas are far more beneficial for their nutrient content compared to any microbial additions.

That seems totally unnecessary. Micronutrients will not wash away easily, and I would just bury the seaweed in the garden to get the full benefit. Bacteria will then recycle the vitamins and add more, specially the B and K complex which is probably what you want. Seaweed is organic matter with micro minerals, vitamin-wise is no different from regular grass clippings or dead leaves.

Thank you both for your answers. This is the first time that I am trying to prepare seaweed tea, which will be used diluted as a foliar spray. I read that it can be applied as a fungicide against powdery mildew, plus all the other benefits.

I also use to mulch my fruit trees with seaweed, as it keeps the soil moist and deters a lot of critters.