As with application of other nutrient sources suitability for a specific site depends on the existing soil mineral content on the site. Soil sampling and testing is used to get an idea what that might be. WSU Cooperative Extension should be able to help you with this.

we use it all the time. After a big storm, usually in November, we go down to a local beach two or three times, load up a picktruck full of kelp ripped from its moorings by the wind, and lying on the sand. We cut it up into foot-long segments with a big kitchen knife on the spot and load it into big garbage bags, It cuts like butter, so the process is quick. We bring it home and unload it in a pile in the yard.

We let the rain of winter soak out the salt, then put it directly under fruit trees, asparagus potato, and annual veggie beds by February. We dig it in slightly. By planting time in April and May, it's mostly deteriorated.

I use seaweed, kelp and other species, as more than half my fertilizer use. The remainder is horse manure. The combination of these two have resulted in a great garden, getting better every year. I'm not a biologist, I just like to grow stuff I can eat. I'm several hundred feet from the beach (Vancouver Island, BC 7b) and use it by the truckload, or even the shopping bagful when I pick it up when riding my bicycle.

Tomatoes grow remarkably well depending on the weather, and my 'native soil' was 5.4 when tested a few years ago. That is all I know about acidity.

Ultimately you might to let the rain rinse it if it drains out of your garden area, but I don't think the surface salt has had a negative effect on any of my vegetables. The weed itself has a high 'salt' content.

I mix it with horse manure and let it sit over the winter, but it can be used immediately, mixing it into the soil before you plant. You can side dress with it or even easier, put it in a large container and fill with water, using the 'seaweed tea' as fertilizer. To use it in pots, use seaweed tea or let it dry and crumble it spreading and mixing it into the soil. I use as much seaweed tea as I have time for, you can't overdo it.

Seaweed as fertilizer is a big plus to me and my garden.