I am in exactly the same situation and I don’t live anywhere near the sea.
I planted about 100 Spring Onion seeds, both red & white.
After about 2 months, they look like blades of very thin, wispy grass.
It is very disappointing.
I am thinking about digging them up and planting potatoes instead.
On the other side of my raised bed, I am growing Broccoli, which is looking great. I have full large stems & leaves.
I have attached an image of my broccoli. On the other side of the wooden divider, are my spring onions. To be honest, I am so ashamed of them, I don’t even want to include an image of them.
You wouldn’t be able to see them anyway. ????♀️