Early spreading plants cover bare ground when it's most appreciated. Puffy mats of creeping or moss phlox (Phlox subulata, Zone 4) spill over low retaining walls or mass on flat ground. Where they get enough bright light, their foliage can be completely covered by a profusion of petals of deep blue and purple, red, pink and white with contrasting “eyes”. Older plants benefit from cutting back after blooming so stems can renew themselves. Other early spreaders are Corydalis lutea, which has yellow flowers (Zone 4) and C. ochroleuca, with white blooms with yellow lip dots and blue-green, ferny foliage that's attractive all season (Zone 5). Corydalis begins blooming when only 15 centimetres high and continues until frost, some reaching 45 centimetres tall, with equal spread. They are generous with their flowers and seeds, and young plants are always available, but they're easily removed where not needed. A good plant for eastern or northern exposures in moist, loamy soil, Corydalis prefers to be out of bright sun.
Two dearly loved plants with ferocious spreading instincts are lily-of-the-valley (Convallaria majalis, Zone 3) and woodland forget-me-nots (Myosotis sylvatica, Zone 5). A true colonizer, lily-of-the-valley spreads by stolons, or “pips”, into advantageous new territory, providing ground cover in dark places where little else grows, such as a shady corner or narrow strip bed shared with ferns. The sweetly scented white bells are perhaps the most classic emblem of early spring. When lily-of-the-valley fades, rambling clumps of forget-me-nots open their hundreds of tiny, sky blue blossoms. Biennial plants that renew themselves with generous seeding, forget-me-nots make a beautiful carpet under early tulips and the Darwin hybrids that follow. They're easily removed where not wanted, but to encourage their growth, shake the seeds from dried clusters over areas where you want them next year.
Plants with strong character are useful in defining garden areas still brown and barren in early spring. The vivid green tufts of maiden pinks (Dianthus deltoides, Zone 5) triumph over lingering snow pockets in the rock garden, quickly sending up 15-centimetre, pencil-straight foliage and extending single, pink flowers in early May. The pinks are happy companions to blue lungwort (Pulmonaria angustifolia, Zone 4), a frost-defiant perennial that begins putting up silver-spotted leaves in the first week of April, followed by clusters of trumpet-shaped flowers opening pink and turning to blue on a compact, 30-centimetre-high clump. Both Dianthus and Pulmonaria remain attractive all season.
Also useful are plants such as the ephemeral Virginia bluebell (Mertensia virginica, syn. Mertensia pulmonarioides, Zone 4), which clumps up and blooms early, April through May, then completely disappears until next year. The nodding bluebell flowers on 30- to 45-centimetre plants are just the ticket to fill in around slow-to-rise peonies, finishing before the peonies expand.