Purple, a color often associated with royalty, has a place in every garden. Purple perennials come in a range of shades, from soft lavenders and mauves to the almost-black of some Oriental irises. A backdrop of tall purple perennials will enhance your garden from spring to fall, accentuating its yellow and orange blooms and harmonizing with its blues, pinks and greens.
Spring: Clematis "Purple Spider"
A native of Holland, the clematis "Purple Spider" is a perennial vine that grows to a height of 10 feet. "Purple Spiders" in the back of your garden supported with trellises or a fence make a tall April and May display of crisp green foliage and deep purple, bell-shaped flowers.
"Purple Spider" is hardy to USDA Hardiness Zone 4, withstanding minimum temperatures as low as -30 degrees Fahrenheit. It needs no pruning and does well in both sun and shade. Like all clematis, it likes its roots to be cool and moist, with its root ball 3-to-5 inches beneath the soil’s surface. It prefers well-drained, acidic soil rich in organic matter.
Spring to Summer: Ornamental Onion
While thinking of onions as ornamental garden plants is a stretch for many people, they haven't seen Allium giganteum. A member of the lily family, giant allium grows up to 5 feet. It puts on a stunning show at the back of a perennial border during late May and June, when its 6-inch densely packed sphere of purple florets tops a thick stem rising from a rosette of silver-green leaves.
Most impressive planted in groups of five to seven bulbs, Allium giganteum likes well-drained soil and full sun. Plant the bulbs 6 inches deep in the fall, spacing them 9-to-12 inches apart. They require staking in high wind and are hardy to average minimum temperatures of -20 degrees.
Late Summer: Joe Pye
Joe Pye (Eupatorerum purpureum), says the Missouri Botanical Garden, is an excellent choice for perennial gardens in Zones 4 through 9. A native Missouri wildflower, Joe Pye grows from 5 to 7 feet tall, producing large, vanilla-scented, light purple blooms from late summer to early fall. It likes sun to partial sun and fertile soil kept evenly moist. Attractive to butterflies, Joe Pye makes an excellent cut flower. Prune its stalks in the winter.
Summer to Fall: New England Aster
Growing from 3 to 6 feet, New England aster (Aster novae-angliae) produces abundant purple daisy-shaped flowers with cheery yellow centers from August to October. Hardy to Zone 3 and temperatures of -40 degrees, this aster provides butterflies with a late-season food source. It needs sun and well-drained rich soil.
Pinching New England aster back--nipping off the very tips of its branches with your thumb and forefinger--midway through its growing season will make it bushier and less likely to need staking. You can grow it easily from seed or find started plants at most nurseries.