|Daylilies by the pond|
Known more for their pretty orange lily-like flower (apparently true lilies are poisonous--don't eat them!), every part of this plant is edible, from its roots to its flowers. Mainly I harvest the tender young shoots of leaves in early spring, just as they appear, and eat them there and then. They taste a bit like a cross between lettuce and onion. When the leaves get bigger, they're a bit too tough to eat raw, and though I've added the flowers and buds to stir fries, I've never tried the roots; I don't have a big enough supply to actually dig them up yet.
Another pretty perennial, campanula has spread itself all around my garden, including along the entire edge of my house where it meets the driveway (there is no soil here, only asphalt). The leaves of campanula are edible, as are its cute purple flowers. I only pick a few here and there in summer, to mix with other salad greens.
Sorrel and rhubarb
I guess people are more likely to know these two are edible! We are more likely to eat both in the spring when there are fewer choices of vegetables in the garden. Both are a bit sour, and for rhubarb, this adds a pleasant tang to savory stews and stir fries; sorrel is more likely to be added to mixed leaf salad like campanula, or if I'm feeling adventurous, a creamy sauce--it goes well on salmon.