Do you ever find yourself recommending the same handful of plants to friends and neighbors? We do. These might not being the splashiest of plants, or even the ones that you’d base an entire design around. But, these are fantastic herbaceous perennials—the meat and potatoes of the garden. To make things even more interesting, we limited ourselves down to choosing just four of these go-to plants. Our choices have multiple seasons of interest, thrive under less-than-ideal conditions, and in our minds, are essential in any great garden.   Expert testimony: Susan Morrison is a garden designer in Concord, California.