“Foods that grow together go together,” so goes the old saying. It’s become the locavore’s anthem, your cue to coax whatever plant life you can from your home ground, and figure out how best to cook it all. And live happily ever after. The seed catalogs that will soon arrive in the mail will tempt you to dream big, and you should. But in which direction? We can’t plant everything. Planning, and alas choosing, is an important part of gardening. You can’t order your seeds if you don’t know what you want to plant, which means you must ponder what you want to eat, and what you can’t get anywhere else. I can always buy carrots at the farmers market, summer and winter, so I don’t need to grow carrots. But it’s harder to get red cranberry beans, to choose one of many heirloom vegetable varieties that one might choose to …