Chocolate Garden
There can be a world of chocolate in your garden. I'm not talking about the plants that look milky brown and have chocolate in the name -- 'Chocolate Ruffles' heuchera (brown foliage) or the 'Chocolate Soldier' columbine (brown flowers) or even 'Chocolate Chip' ajuga (its new leaves are brown). No, we're talking about walking through the garden and smelling chocolate. A sniff of the plants below can be very satisfying. Unfortunately though, if aroma makes you hungry, you'll need to carry a chocolate bar with you. The only two of these that are edible (the geranium and the mint) have only the vaguest of chocolaty flavors.
Chocolate Flower

(Berlandiera lyrata)
The chocolaty aroma that wafts from these dark-eyed daisies is best in the morning. A wildflower that's native to the Southwest, the chocolate flower thrives on minimal water. In moist, humid climates, try planting in containers; that will also allow you to place the plant where you can best appreciate its fragrance. This hardy perennial is short-lived but freely reseeds.
Chocolate-Mint Geranium
(Pelargonium tomentosum 'Chocolate Mint')
Scented geraniums come in apple, pineapple, orange and even pink champagne, so obviously a chocolate-mint was needed, too. The foliage, not the flowers, carry the fragrance. Enjoy as an annual during the growing season and then bring inside for the winter.
Chocolate Mint

(Mentha x piperita 'Chocolate Mint')
Call the fragrance on this mint nine parts mint to one part chocolate. Like others in its family, this mint spreads aggressively via rhizomes. If you want to keep it inbounds, plant in containers or install ground barriers. Mint is tolerant of almost any soil, but in moist, rich soil, growth will be rampant.
Chocolate Cosmos

(Cosmos atrosanguineus)
Velvety, black-maroon flowers give off a wonderful chocolate scent from midsummer to fall. This plant needs full sun and well-drained soil with even moisture. In spring, plant tubers 3 feet apart in full sun. In the fall, treat as you would a dahlia; lift and store for the winter. Enjoy the aroma but don't eat: This plant is toxic.
Not on the list:
Somehow the sweet shrub (Calycanthus floridus) has gained the reputation for having a chocolate aroma. Not so. The brown-maroon flowers of the sweetshrub have a lovely fragrance, but it's fruity (or sometimes spicy). The other common names for this large deciduous shrub: strawberry bush, spicebush and Carolina allspice.
Source for chocolate flower: Mountain Valley Growers