Hey, that’s a fair question! Thanks to whoever telepathically sent it. I have a feeling you know what us regionally-focused seed growers are going to say, but then again, maybe not! We try to be straight talkers over here and want you to have the facts whether they serve us or not.
While of course we’d be giddy if folks got all their seeds from local seed companies, buying regionally appropriate varieties matters more for some crops than for others. For example, if you plant whatever lettuce, spinach, or radish seed your local hardware store sells, you’ll probably do just fine. Those are quick, easy crops that don’t require a long ripening period or a ton of heat units to do their thing.
However, random tomato, pepper, eggplant, melon, corn and winter squash varieties are higher risk propositions. Ripening Brandywine Tomatoes in Tacoma or California Bell Peppers in Portland are far from guaranteed. However, with a Scotia Tomato (named for chilly Nova Scotia) or a Mini Red Bell Pepper (nice and small for quick ripening) Northwesterners and other cooler location growers have a high chance of high yields. The shorter the Days to Maturity the merrier for these heat lovers.
So yes, you can grow watermelons in Washougal, WA, so long as it’s the right variety.