Aubrieta 'Rock On Blue'

Aubrieta 'Rock On Blue': A Periwinkle Waterfall for Stone Walls

'Rock On Blue' plays the blues, but it's the happiest blues you've ever heard. Sheets of blue-purple flowers pour over rocks and walls in spring while everything else is still tuning up. OPENING ACT. HEADLINER ENERGY.

Plant Characteristics:

• Botanical Name: Aubrieta gracilis 'Rock On Blue'
• Common Name: Rock Cress
• Height: 10–15 cm (4–6 in)
• Spread: 40–50 cm (16–20 in)
• Flowers: Small four-petalled blue-purple flowers with a tiny yellow centre, covering the plant in spring
• Bloom Time: Spring (April to June)
• Foliage: Grey-green, mat-forming and semi-evergreen

Where to Plant: Let it spill over a retaining wall, tuck it between stepping stones or run it along the front edge of a sunny bed. It's a natural for rock gardens, gravel gardens and the rim of a large container. Because it loves lean, fast-draining soil, it suits hot, dry spots near walkways.

Companion Plants: Spigelia 'Little Redhead' brings red tubular flowers in June and July, a bright follow-up to the blue spring carpet. Sagina 'Aurea' makes a golden mossy mat only 2 to 5 cm tall, perfect between stepping stones nearby. Leucanthemum 'Snowcap' adds compact white daisies from June to August. This low, sunny group works well along a path or wall.

Plant Care: Plant in full sun to part sun, in lean, sharply drained soil. Gritty, sandy or limestone-based soil is ideal; rock cress dislikes wet feet, especially over winter. If you have heavy clay, plant it on a slope, in a raised bed or between stones. Water through its first season, then only during long dry spells. Shear the plant back by about half right after it finishes flowering. That keeps the mat dense and tidy and can bring a light second flush. Don't cut it back in fall, and don't pile mulch over the crown. Rock cress is best left undivided while it's thriving. Older mats that open up in the centre can be refreshed by division or by rooting a few cuttings in early fall.

History: The genus Aubrieta was named in 1763 by the French botanist Michel Adanson in honour of Claude Aubriet, a French painter of flowers and natural history. Its twenty or so species come from the mountains and rocky slopes of southeastern Europe and western Asia.

Final Thoughts: Tuck it into a rock wall, skip the watering once it settles in, and let the early bees grab front-row seats. ROCK ON, INDEED.