1. Elderberry (Sambucus ‘Black Lace’). Cut back this fast-growing shrub in the spring, and it will still grow to eight feet by midsummer. Its pink flowers contrast elegantly with its leaves, and its dark berries can be used to make elderberry wine. Use in a mixed border, or plant en masse as a hedge. Zone 4. Sun.
2. Petunia (Petunia ‘Black Velvet’). A cool-season annual with the deepest black flowers of any petunia. Plant in the spring and fall to get the best color and show. Zone 5. Sun to partial shade.
3. Black Tree Aeonium (Aeonium aeonium var. artropurpureum ‘Schwarzkopt’). This is a fine option for containers in dry, sunny locations or as a houseplant. Its yellow flowers are a refreshing foil to its dark leaves. Zone 10. Sun.