Rock cress
Arabis caucasica · Brassicaceae
A grey-green mat smothered in white flowers in early spring, scented of honey. It likes cool summers and sharp drainage.
- Size
- 8 in tall, 18 in wide
- Zones
- 4 to 7
- Light
- Full sun
- Flowers
- Mid April to early May
- Pets
- No toxicity recorded
- Job in a bed
- Carpet
A bed built around rock cress
The planner designed this bed around rock cress when this page was made: a 12 × 6 ft (3.7 × 1.8 m) naturalistic planting in zone 6, full sun. It chose the other plants from the 715 that suit those conditions and its dry soil, and says below why rock cress stands where it does.
The plants
- 1 Rock cress × 16, white
- 2 Sea thrift × 8, pink
- 3 Switchgrass 'Cheyenne Sky' × 3, purple
- 4 New England aster 'Alma Pötschke' × 3, pink
- 5 Silver sage × 1, silver leaves
- 6 Butterfly weed × 3, orange
- 7 Star of Persia × 3, purple
- 8 Pink lily leek × 12, pink
Why this plant
- Part of the matrix. The low fabric of grasses and groundcovers that the taller plants come up through.
- The only dense clusters. The others are globes, airy sprays, daisies and others. Shape reads at a distance, where colours blur.
- The only white. White sits between stronger colours and calms them.
Why here
- Under the taller plants. It runs back between them as living mulch: there its job is to cover the soil, not to be looked at.
- 16 plants in 4 groups (9, 3, 3 and 1). Seen again further along, the same plant ties the bed together.
- Fine leaf against bold. Silver sage is beside it: the strongest contrast of leaf there is.
Why now
- In flower for five weeks. From mid April to early May.
- Opens the season. For its first four weeks nothing else on the plan is in flower.
Planned as a naturalistic planting: low grasses and groundcovers, the matrix, make up 44% of the planted ground. The bed is balanced: the left half carries 45% of the visual weight and the right half 55%. The scheme leans cool (pink and purple) and uses orange for warmth, with white to calm things between them.
The planner's own design check: 13 Excellent, 4 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where rock cress goes in a border
At 8 in it belongs at the front of a bed. In the planner's ten height classes it is low (6 to 12 in).
Its job: carpet. A groundcover planted in threes and fives to cover the soil: along the front, and just behind it.
With aubrieta and basket-of-gold it makes the classic spring wall planting: white, purple and yellow together. Shear it after flowering to keep the mat dense.
- Tumbling over walls and rocks
- A spring carpet with bulbs
- Edging in cool climates
What to plant with rock cress
Plants recorded as good partners for it, and what each pairing does:
- Aubrieta: in flower together for five weeks, from mid April; happy in the same dry soil.
- Basket-of-gold: in flower together for four weeks, from mid April; happy in the same dry soil.
- Creeping phlox: in flower together for four weeks, from mid April.
Questions about rock cress
Does rock cress need sun or shade?
Rock cress grows in full sun (6 or more hours of direct sun a day).
It wants dry, sharply drained soil, on the lean side, with no feeding, and little watering once settled. Once settled in, it stands drought.
What zones does rock cress grow in?
USDA zones 4 to 7. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).
Above zone 7 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does rock cress flower in my zone?
In zone 5 it flowers mid April to early May. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.
| Zone 4 | Mid April to mid May |
|---|---|
| Zone 5 | Mid April to early May |
| Zone 6 | Early April to early May |
| Zone 7 | Late March to late April |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should rock cress be planted?
12 in (30 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 18 in (45 cm), so a group knits into one patch.
It grows 8 in (20 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many rock cress plants do I need?
At 12 in apart, set out in staggered rows:
- 12 to fill 10 square feet (about 1 m²)
- 11 for a single row 10 ft (3 m) long
- 38 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as threes and fives, along the front and just behind it.
In the bed above, the planner used 16 in four groups.
Is rock cress poisonous to dogs and cats?
No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.
"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.
Do deer eat rock cress?
Mostly not. NC State lists it as resistant to deer and rabbits. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.
What flowers after rock cress?
Rock cress is over by early May. These start as it finishes and carry the same spot on, so it never goes flat:
- Creeping thyme: from early June to mid July, 3 in tall, to stand in front of it and cover its fading stems.
- Lady's mantle: from late May to early July, 18 in tall.
- Catmint 'Walker's Low': from mid May to mid September, 24 in tall.
What does rock cress look like in winter?
Rock cress holds some of its leaves into winter, more in a mild year or a sheltered spot, and they look tired by March. Cut the old ones off as new growth starts.
Is rock cress good for bees and butterflies?
Rock cress is visited by pollinators, bees, specialist bees and butterflies.
It is native to the United States.
In these guides
- Deer-resistant perennials for full sun
- Rabbit-resistant plants
- Drought-tolerant perennials for full sun
- Pet-safe plants for a sunny border
- Native perennials for pollinators
- Plants for butterflies
- Plants for bees
- Low plants for the front of a border
- Groundcover plants
- Plants for a white garden
- Silver and grey-leaved plants
Every fact on record
- Type
- Perennial (groundcover)
- Size
- 8 in (20 cm) tall, 18 in (45 cm) wide
- Plant
- 12 in (30 cm) apart
- Height class
- Low (6 to 12 in)
- Place in the bed
- Front
- Flowers
- Mid April to early May; dense clusters; white, pink
- Leaves
- Fine texture, semi-evergreen; grey-green
- Shape
- Mat-forming, spreading
- Hardy in
- USDA zones 4 to 7
- Light
- Full sun
- Soil
- Lean, dry and sharply drained
- Water
- Low
- Feeding
- None needed
- Family
- Brassicaceae
- Comes from
- Mediterranean, Crimea, Turkey, Iran, Causcus
- Attracts
- Pollinators, bees, specialist bees, butterflies
- Stands up to
- Deer, rabbits, drought, heat, poor soil
Checked against NC State Extension and VASCAN (plants of Canada). Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.