White is a pleasing color which shows brightly in daytime or dusk. Because white goes with every other color, it is effective placed in between plants with disparate flower colors and can bring together elements of the garden that might not otherwise look good together.
Many gardeners have areas of their flowerbeds filled with only white-flowering plants. A garden with only white flowers is called a "moon garden" because the color white shows up so clearly at night. Planting white-flowering perennials where they are visible from windows or patios can create garden interest in the evening.
Snowflake catmint (Nepeta x faassenii 'Snowflake') is a small perennial that blooms all summer long. Its white blooms are attractive to hummingbirds, and the foliage is fragrant and attractive to cats.
Snowflake catmint grows to 14 inches tall and wide, requires full sun to bloom well, and thrives in U.S. Department of Agriculture Plant Hardiness Zones 5 to 9. It looks excellent massed between other shrubs or perennials.
White Cape Fuchsia
White cape fuchsia (Phygelius x aequalis 'Snow Queen') has crisp white flowers held above medium to dark green foliage. It blooms all summer long and the bell-shaped blooms have the added benefit of attracting hummingbirds.
White cape fuchsia reaches 2 to 3 feet tall and wide, and needs full to partial sun. It grows well in USDA zones 7 to 10 and prefers sites with well-drained soil. The color of this cape fuchsia shows up brightly in moon gardens.
Casablanca Peruvian Lily
Casablanca Peruvian lily (Alstroemeria 'Casablanca') is a white-blooming flower that reaches 3 to 4 feet tall and thrives in full sun on the coast, or partial shade elsewhere. The white flowers have subtle yellow and pink markings, so it harmonizes well with yellow or pink roses.
Casablanca Peruvian lily is hardy in USDA zones 7 to 10, and makes an excellent cut flower because the cut blossoms last up to two weeks in a vase.
Dwarf Goat's Beard
Dwarf goat's beard (Aruncus aethusifolius) is a shade-loving perennial with bright white cone-shaped blooms in summer. The leaves are finely cut and have a texture like that of a fern.
Dwarf goat's beard is easy to grow in shady sites with regular watering, and it is hardy in USDA zones 3 to 9. It grows 18 inches tall and wide, and complements woodland gardens.
Holly's White Penstemon
Holly's white penstemon (Penstemon 'Holly's White') is a pure white-blooming perennial that grows to 3 feet tall and wide. The spikes of hanging, bell-shaped blooms attract hummingbirds, and penstemon is deer-resistant. This penstemon's foliage is medium green. Holly's white penstemon blooms in summer and grows in USDA zones 4 to 9.