Aubrieta 'Rock On Purple'

Aubrieta 'Rock On Purple': A Purple Waterfall Over the Stone Wall

Spring shows up and 'Rock On Purple' is already draped over the wall in a purple velvet cape. Low, grey-green and tough as old boots, it takes the driest sunny spots without asking for a dressing room. DIVA LOOKS. ROADIE WORK ETHIC.

Plant Characteristics:

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

Where to Plant: Plant it at the top of a retaining wall so it can cascade, tuck it into a rock garden, or use it to edge a sunny path or gravel bed. It's also handy along the rim of a large container. It's built for lean, sharply drained soil, so it's happiest in hot, dry spots where lusher plants give up.

Companion Plants: Let 'Rock On Purple' tumble over the front of a sunny, well-drained bed with magenta, red and blue to follow. Sedum 'Fulda Glow' creeps at 5 to 10 cm with bronze leaves and red flowers from July to September. Dianthus Fruit Punch® 'Cranberry Cocktail' adds double hot magenta pinks at 20 to 25 cm from June to August. Lavandula 'Hidcote Superior' brings fragrant deep violet spikes at about 40 cm from June to September. Bouteloua curtipendula stands behind at 60 to 75 cm in flower, a native side-oats grama.

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: Deer leave it alone, bees treat it like an early breakfast buffet, and you get to take the credit. THE ROCKERY HAS A NEW FRONTMAN.