Summer is short in Finland and spring is even shorter. In southern Finland there is often snow on the ground at the beginning of April, with a few crocuses poking their heads through the bare patches. Of all the seasons, spring is definitely the most versatile depending which part of Finland you are visiting. In the North it is still possible to go skiing where as South is getting warmer and warmer.
If the Finnish archipelago and long Baltic coast make you think about beautiful summer days filled with sailing and boating, you are definitely on the right track. But the Finnish coast invites you for many great experiences throughout the year.