Perennial flowering bulbs, according to the University of North Carolina Extension, are those that can remain in the soil and bloom for three straight years. Bulbs' hardiness--the degree to which they can survive winter cold--differs from family to family. Not every bulb will perennialize everywhere. Plant spring and early summer blooming perennial bulbs the previous fall in soil below 60 degrees F. Plant late summer and autumn bloomers after the final spring frost.
Hyacinths send their green shoots out of the soil between March and April and reach full bloom between mid-April and May. Their blooms are densely packed "cylinders" of fragrant single tubular on 8 to 12 -inch stems. Flowering lasts from two to three weeks.
Most effective when planted in groups of at least six bulbs of the same color, hyacinths are available in white, deep blue, purple, pale yellow, orange, red and several shades of pink. Hyacinth bulbs are generally hardy to temperatures of -23 degrees F.
Plant the bulbs in full sun with their bases 8 inches beneath the soil's surface. Set them 1 to 3 inches apart, depending on size They will perennialize in US Hardiness Zone 4 with a 3-inch mulch layer and without mulch in Zones 5 to 7. Keep the plants moist during the growing season.
Blooming even earlier than hyacinths, dwarf iris (iris reticulata) flowers for two weeks in March and April. Only 5 to 6 inches tall, dwarf iris is hardy to 14 degrees F. Its showy single 2 1/2 inch flowers, dark blue to purple with white and gold markings, pair well with purple and gold crocuses. Their fragrance is a bonus.
Dwarf iris, says the Missouri Botanical Garden, does well in well-drained sunny spots with average soil. Plant the mottled bulbs in the fall between 3 and 4 inches deep and the same distance apart. To encourage future blooms, keep the soil moist while the plants are growing and on the dry side when they are dormant.
Plant Asiatic lilies in the fall or spring for three weeks of summer flowering. These 2 to 4-foot high plants produce single stems with narrow pointed deep green leaves topped by spikes of staggered buds. The trumpet-like flowers open in stages, beginning with the lower ones. Cut Asiatic lily stems, especially fragrant ones like Stargazers, make excellent additions to floral arrangements
Asiatic lily cultivars grow in enough colors to suit any gardener's palette. White, yellow, pink, red, orange and combination flowers are available. Plant the bulbs in groups of three or more. Choose sunny to partly shady locations with acidic soil rich in organic material. Place the bulbs 4 to 6 inches apart with their bases are 8 inches beneath the soil surface. Mulch them in US Hardiness Zones 3 and 4, and water them regularly during their growing season.