Small plants that flower in the summer make the most impact when when planted along borders or in front of other, larger plants. The small plants add color and appeal in rock gardens and in hanging baskets and containers. Small, flowering plants also help fill in gaps between other plantings, or they work well by themselves in gardens with limited spaces.
Lily-of-the-Valley (Convallaria majalis)
Blooming in late spring to early summer, lily-of-the-valley produces highly fragrant bell-shaped blooms. The plants work well under hedges or trees where they receive dappled sunlight. The perennial plants grow up to 9 inches in height and feature dark green leaves with a stalk containing the perfumed white flowers. The flowers last about 3 weeks, followed by berries that turn red when ripe. Lily-of-the-valley spreads through rhizomes. The plants grow in hardiness zones 3 to 7, preferring slightly acidic, moist soil, and it makes a great ground cover. They also look very attractive when planted in drifts.
Common Blue Violet (Viola sororia sororia)
The delicate purple blooms of the woolly blue violet last well into June, making this shade-loving plant ideal for moist areas of the garden or in rock gardens. The native plant grows up to 6 inches in height, with the flowers sitting slightly above the leaves. The perennial plant produces soft seeds that attract ants who help distribute the seeds to other areas of the garden. Violets prefer slightly acidic, rich soil in partial sun or light shade in hardiness zones 3 to 7.
Edging Lobelia (Lobelia erinus)
As its name implies, edging lobelia woks great as an edging plant with its bright blue flowers blooming during the summer. The annual plant grows up to 8 inches in height and width, thriving in hardiness zones 3 to 11. Edging lobelia grows in moist, well-drained soil in full sun or partial shade although it requires full shade in hot climates.
Creeping St. John's Wort (Hypericum calycinum Linn)
Creeping St. John's Wort grows to 12 inches in height with a spread of about 18 inches. The plant features large bright yellow blooms that appear in June and July with each flower lasting a few weeks. The perennial, drought-tolerant plant grows in hardiness zones 6 to 11. The easy-to-grow plant prefers sandy, alkaline soil, but it thrives in almost any soil type in sun or shade.
Sweet Alyssum (Lobularia maritime)
For summer-long blooms requiring little maintenance, sweet alyssum makes a great choice. Sweet alyssum grows up to 12 inches high with clusters of tiny white blooms that add a sweet perfume to the air. The drought and heat-resistant plants thrive in full sun to partial shade and grow in almost any soil type in hardiness zones 1 to 11.