When you're deciding which shrubs to add to your perennial garden, go for the ones that provide ornamental value when various perennials (and annuals) have finished blooming.
Dwarf fothergilla (Fothergilla gardenii). This two- to three-foot plant has definite three-season appeal. In April the honey-scented flowers, resembling little bottlebrushes, appear before the foliage. The leathery dark green leaves become one of nature's truly glorious sights in fall; the colors range from bright yellow to orange to scarlet all combined on the same leaf.
Fothergilla grows best in acid, peaty, sandy loam. It tolerates partial shade, but for great fall coloration it needs full sun. It also needs good drainage. Hardy in USDA Zones 5 to 8
Slender deutzia (Deutzia gracilis) 'Chardonnay Pearls'. In spring the plant is covered with a plethora of beautiful white buds that pop open to emit a delicate fragrance. This three-foot shrub also has lovely lime-yellow foliage that provides color from spring to fall.
Slender deutzia does well in average garden soil. In hot climates it does best in partial shade; in cooler climates it can take morning sun but needs shade in the afternoon. Hardy in USDA Zones 4 to 8
'Little Henry' sweetspire (Itea virginica 'Little Henry'). In early summer sweetspire produces long, slender and sweetly fragrant white blooms that can easily last for two months. Butterflies love the flowers.
A compact three-foot plant, sweetspire prefers moist, fertile soils in full sun to partial shade. During the summer the leaves are a distinct bright green, then turn scarlet and crimson in fall. Hardy in USDA Zones 5 to 9
'Petit Bleu' blue-mist shrub (Caryopteris x cladonensis 'Petit Bleu') is only 24 to 30 inches tall. Against the dark green, aromatic foliage, the dark blue flowers look almost fluorescent. You can expect a dazzling floral display from late summer through fall. 'Petit Bleu' grows in average garden soil in full sun.
'Sunshine Blue' bluebeard (Caryopteris x incana). This late bloomer sports striking amethyst-blue flowers, and the leaves are a magical sunny yellow; the contrast on the three-foot shrub is astounding.
'Sunshine Blue' grows best in full sun and in cooler climates, but in hotter areas it does better in partial shade or some filtered morning sun.
Once they are established, 'Sunshine Blue' and the even smaller 'Petit Bleu' (2 to 2 1/2 feet) benefit from cutting back in late winter or early spring. They are cold hardy to USDA Zones 5, but it's best to mulch for protection there. USDA Zones 5 to 9; mulch for extra protection in Zone 5.
'Purple Emperor' butterfly bush (Buddleia davidii). Many versions of butterfly bush range from 10 to 15 feet tall, but 'Purple Emperor' is only four to five feet. It blooms from summer through fall, making it a good background plant for shrub or perennial borders. 'Purple Emperor' is as floriferous as its taller cousins and is quite well-behaved.
Butterfly bushes grow in full sun and average well-drained garden soil. After the plant is established, cut it back in early spring to rejuvenate and increase flower size. Hardy in USDA Zones 5 to 9