How to Plant and Grow Rock Cress

Rock cress (Aubrieta deltoidea) is one of several plants going by the common name of rock cress. This perennial forms splendid mats of color in the spring and—as the name implies—is at home in a rock garden and its associated well-drained soil. Rock cress works exceptionally well along walls, borders, and underneath spring-blooming bulbs to add color to a garden.

With its compact, low-growing habit, rock cress acts as a color filler in the lower levels of the garden. For most of the growing season, these plants are a rich green, but during spring, they explode into mounds of blooms, ranging from the lightest pinks to the richest purples. The flowers of rock cress are borne so fully that you cannot see the foliage. If this four- to six-week spectacular display of flowers is too short for you, look for varieties with variegated foliage in either white or gold to continue the colorful display.

Where to Plant Rock Cress

Plant rock cress in well-draining soil. It thrives in rock gardens and is attractive along walls and in borders. Rock cress adds stunning contrast when planted under spring-flowering bulbs. The rock cress flowers are small but give off a lovely scent; plant some along a path to enjoy the fragrance.

While rock cress plants are grown most often in the ground, they do well in containers for an eye-catching spring show.

See more of the best plants for rock gardens here.

How and When to Plant Rock Cress

The best times to sow rock cress seed are spring and fall. The plants will bloom the first year only if they are planted very early in spring; in most cases, they start blooming the second year and then every year after that. Press the seeds into the soil after the last frost of spring but don't cover them. They require light to germinate. The seeds can also be started indoors four to six weeks before the last frost.

Sowing seeds in a rock garden or on a vertical surface requires some special care. Mix the seeds with a small amount of sand and blow them into the rock garden crevices, or combine the seeds with gelatin and spread it on vertical surfaces, pressing it into any crevices. Mist regularly but sparingly until germination occurs.

When growing from seedlings or nursery plants, set them in well-draining soil at the same depth they were in their containers. Space rock cress plants 15 to 18 inches apart; they spread rapidly to form a dense mat of foliage.

Rock Cress Care Tips

Rock cress plants require relatively little care after they are established.

Light

Rock cress thrives in full sun. In less than full sun, the blossoms are not as bright or plentiful.

Soil and Water

These plants hail from tough mountainous terrain, so you can probably guess their primary requirement is well-drained soil. The fact that they are often found in some of the smallest cracks or pure gravel gives you an idea of how sharply drained the soil needs to be for rock cress to thrive. Due to its rocky upbringings, this plant prefers alkaline soil.

This plant is extremely drought-tolerant and grows well in a container. Water it only when the soil is dry. Be careful not to overwater rock cress or plant it in a moist area because too much moisture will kill it.

Temperature and Humidity

Rock cress grows best in warm temperatures between 65°F and 70°F. In warmer zones, it benefits from some shade in the afternoon. It grows well in low to mid-range humidity. High humidity may shorten the length of the perennial's life.

Fertilizer

Rock cress doesn't require any fertilizer, but it benefits from a high-nitrogen fertilizer when the plants are first set in the garden and a phosphorus fertilizer after they bloom.

Pruning

After their spectacular display of flowers, rock cress benefits from a shearing to stay nice and neat. If you leave spent blossoms on rock cress, there is an excellent chance the plant will reseed. Consider this a benefit because rock cress can be somewhat short-lived as a perennial. Although they don't tend to be invasive, you can control where you want more rock cress by sprinkling the seeds.

Potting and Repotting Rock Cress

Drought-tolerant rock cress grows well in containers, but it prefers alkaline soil (a pH higher than 7.0). Most commercial potting soils are neutral or slightly acidic. Increase the pH if necessary by adding crushed egg shells, wood ashes, or baking soda. Don't overwater the plant; too much water will kill it.

Pests and Problems

Rock cress doesn't usually attract many garden pests, although they sometimes attract aphids and flea beetles.

In areas with warm, humid summers, rock cress may have a shorter life span. Plant them in part-shade to increase their longevity.

How to Propagate Rock Cress

Gardeners can propagate rock cress by seed, clippings, or division.

Seed: Seed sown directly in garden soil in spring or fall is the easiest way to propagate rock cress. Gardeners can harvest the seed from mature plants in the fall—or do nothing. Rock cress will self-seed with little encouragement required.

Cuttings: Take stem cuttings from a mature rock cress plant in the spring. Remove excess foliage from the bottom half of a cutting and dip it (including a growth bud) into rooting hormone. Put the cutting in a pot filled with sterile potting soil or perlite, and water it well. Place it in a warm, bright-light location and watch for new growth.

Division: In the fall, dig up a mature rock cress plant and use a sharp knife to divide the root ball into two or three sections, each with healthy roots and foliage. Replant them immediately.

Use these plants for a no-fail trough garden

Types of Rock Cress

'Aurea Variegata' Rock Cress

The Aubrieta deltoidea 'Aurea Variegata' cultivar features bright gold and green leaves and blue-violet flowers. This semi-evergreen perennial grows up to 4 inches tall and forms an excellent groundcover. Zones 4-8

'Barker's Double' Rock Cress

Aubrieta deltoidea 'Barker's Double' offers attractive double blue-purple or pink blooms. It grows up to 4 inches tall. Zones 6-9

'Red Cascade' Rock Cress

Deep magenta-red flowers dominate Aubrieta deltoidea 'Red Cascade', This mounding perennial reaches up to 6 inches tall. Zones 4-9

'Variegata' Rock Cress

Aubrieta deltoidea 'Variegata' has gray-green leaves with creamy margins. It is available with blooms in several colors, including dark purple, violet-blue, pink or white. It grows to 6 inches tall. Zones 4-8