Honestly, I sometimes think you could throw an almost random selection of vegetables in a pot and bring them to a boil and wind up with something pretty tasty — if you know what you’re doing. Here are a few guidelines.
Choose carefully: Let me start by apologizing for that word “random.” In cooking — or at least good cooking — nothing is truly random. But you’d be surprised how far you can get by sticking with that old local-and-seasonal thing. Potatoes, fennel, winter squash and greens? I can think of half a dozen dishes without even trying.
You need starch: It gives soup heft. If you’re using pasta, rice or grains, cook them first and add them at the end so they don’t muddy the broth or overcook. If you’re using potatoes, use smooth-skinned boilers and add them early, so they have time to absorb flavors.
When in doubt, add greens: And then if you’re still uncertain, add more greens. I don’t know a cook who doesn’t have a few bags of odd scraps of lettuce, kale and chard in the crisper drawer. Soup is a great way to get the most out of them, and the more (and the more kinds), the merrier.