Blue is always a welcome color in the garden. It brings calmness and serenity; can cool down reds and orange or provide contrast with yellow. Blue flowers go well with its many shades of green suggesting water and the sea. Pair it with white to add crispness, or with red and white to make a patriotic statement. Unfortunately, however, blue blooming plants are not in abundance and gardeners treasure the ones that are available.
Here are five perennials for the rock garden with blue flowers.
Globe Daisy (Globularia cordifolia)
The light blue flowers that appear on short stems in late spring to early summer look like small blue powderpuffs. Creeping stems root as they grow and eventually form a mat with small leathery-looking leaves.
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Size:5” H 12” W
Light: Full sun; tolerates some shade
Soil:Average, well-drained
Hardiness:Zones 4-9
Alpine Aster (Aster alpinus)
Violet-blue yellow eyed-daisy-like flowers 1-3” wide are borne in summer over basal clumps of light gray-green leaves. Cultivars are available in lavenders, pinks, purples, and white.
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Size: 6-9” H x 12” W
Light: Full sun
Soil: Average, well-drained
Hardiness: Zones 4-7
Grass-Leaf Scabious (Scabiosa graminifolia)
Lilac-blue flat flower heads 2” across are borne above a low mound of silvery, mostly basal narrow leaves in summer. A long blooming plant, grass-leaf scabious tolerates some heat but not with high humidity.
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Size: 10-18”H x 18” W
Light: Full sun
Soil: Average, reasonably well-drained, neutral to alkaline
Hardiness: Zones 5-10 (but not in climates with heat and humidity)
Woolly Speedwell (Veronica incana)
Eight inch spikes of deep blue flowers are produced over low clumps of silvery foliage over a long period in summer. Pink cultivars are also available. Does not tolerate heat and humidity well and will rot if soil is too moist.
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Size: 12-18” H x 18” W
Light: Full sun; tolerates some shade
Soil: Average, well-drained
Hardness: Zones 3-10 (does not tolerate high heat and humidity)
Crested Gentian (Gentiana septemfida)
Considered a quintessential rock garden plant, all gentians are valued for their clear blue flowers. Crested gentian bears small clusters of flowers on arching stems in late summer. Although it can stand some heat it can not tolerate heat with humidity.
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Size: 18”H x 18” W
Light: Bright but shaded from direct sun
Soil: Rich, high in organic mayter, moist, well-drained, acid to neutral
Hardiness: 3-7 (with heat and humidity) 9 (with low humidity)
These blue flowered perennials span the gardening season from late spring to fall. Globe daisy begins with its powder puff-like flowers followed by alpin aster with cheery yellow centers. Scabious and wooly speedwell, the former with flat heads, the latter with spikes, follow with a long bloom period. Crested gentian follows in late summer.
