Prostrate cabbage: complete guide

Overview

Prostrate cabbage (Brassica procumbens) is a low, creeping relative of the common cabbage from the Brassicaceae family. The plant occurs naturally on the coastal cliffs and rocky slopes of Algeria and Tunisia, and has since naturalised on Corsica as well. In Italy, where the species once grew on the Tuscan Archipelago, it is now extinct: a quiet reminder of how fragile narrow coastal endemics can be.

The species name procumbens ("lying down" or "creeping") describes its growth habit directly: instead of an upright shrub like most cabbage relatives, this plant forms a low, flat mat that presses tightly against the rocky ground, an adaptation to the constant wind and salty air of its coastal cliff habitat. For rock gardens and wall plantings it is an unusual, low-growing groundcover with striking yellow flowers.

Botanically, prostrate cabbage is closely related to Corsican cabbage (Brassica insularis), but where that species forms an upright shrub, this one evolved a completely flat, creeping habit instead. That difference in growth form makes the two an interesting pair to study side by side in a Mediterranean rock garden collection, and it explains neatly why prostrate cabbage suits spots where an upright shrub would simply catch too much wind.

Appearance and bloom

Prostrate cabbage forms dense, creeping mats of grey-green, fleshy foliage that lie flat against the ground, rarely exceeding 10 to 15 cm in height but spreading 40 to 50 cm wide. The leaves have a somewhat salt-tolerant, compact structure typical of plants growing on windswept sea cliffs.

In spring, typically from April to June, small, cross-shaped yellow flowers appear above the foliage, characteristic of the cabbage family. The flowers grow in loose clusters and attract early pollinating insects. After flowering, short seed pods form, ripening brown over summer.

Ideal location

Give prostrate cabbage a spot in full sun on a rocky, fast-draining surface: a wall crevice, a rock ledge or a raised gravel bed best mimic its coastal cliff habitat. The plant tolerates wind and salty sea air extremely well, and slightly neglected, lean terrain actually produces the compact, dense growth habit that is most valued.

As a trailing plant over a low wall or in a crevice between rocks, the creeping habit shows to best effect. Avoid a shady or moist spot: there the plant becomes soft and leggy instead of compact.

Soil

The ideal soil is lean, coarse-textured and extremely well-drained, with a pH between 7.0 and 8.0. Lime-rich, even slightly salty soil is tolerated well, matching its coastal cliff origin. Rich, moisture-retentive garden soil is unsuitable and leads to root rot.

When planting, mix in plenty of grit or coarse sand, at least 40 to 50% of the volume. In containers or wall crevices, use a coarse potting mix with extra perlite or lava grit added. Feeding is essentially unnecessary.

Watering

After planting, water prostrate cabbage regularly for the first few weeks to let the roots establish, roughly once a week. After that, the plant is highly drought-tolerant and needs almost no supplemental water in summer.

Overwatering, especially in winter, is the fastest way to lose this plant: waterlogged soil is more dangerous for this species than sharp cold. Always let the soil dry out fully between waterings.

Pruning

Pruning is minimal. Remove faded flower clusters after blooming to keep the mat tidy, unless you want to collect seed yourself. Old, bare sections of the mat can be trimmed back in spring to encourage denser new growth.

Because the plant naturally stays low and creeping, no further shape-pruning is needed.

Maintenance calendar

March: check drainage after winter and remove dead foliage.

April-June: main bloom with yellow flowers; pollinators active.

July-August: seed pods ripen and dry; minimal watering during heat.

September-October: a good time for cuttings or topping up the gravel around the mat.

November-February: winter rest; protect against prolonged frost combined with moisture.

Winter hardiness

Prostrate cabbage originates from a mild North African coastal climate and suits USDA zone 9 to 10, meaning it tolerates little frost: typically no more than light overnight frost down to -3°C to -5°C. In the Netherlands, Belgium and Germany, winter protection is therefore almost always necessary.

The plant is best grown in a pot moved to an unheated greenhouse or sheltered wall in winter, or planted in an exceptionally well-drained, south-facing rock crevice and covered with frost fleece when frost is forecast. Wet soil combined with cold is the main cause of death.

Companion plants

Prostrate cabbage combines well with other low, drought-loving rock plants: thyme species, Sedum, and Aurinia saxatilis (basket-of-gold), which also belongs to the cabbage family and makes an attractive bright yellow-flowering relative. Iberis and low Alyssum species also fit well in the same planting scheme.

In a Mediterranean rock garden it pairs with Cistus and low succulents that appreciate the same lime-rich, lean soil and full sun. For a lively coastal scene, complement the mat with Armeria maritima (sea thrift) and low Euphorbia species, which likewise thrive in windy, rocky spots and time their bloom nicely alongside the yellow flowers of prostrate cabbage.

Propagation

Propagation is by seed, sown in spring in a free-draining, lime-rich seed mix; germination takes 2 to 3 weeks at 15 to 18°C. Because the species is rare in the wild and even extinct in Italy, seed is mainly found through specialist botanical nurseries and seed banks for Mediterranean rock plants.

Cuttings of young shoots in summer usually root within 3 to 5 weeks in a sharp, moist cutting medium and are a reliable way to propagate an exact copy of the parent plant.

Pests and diseases

Prostrate cabbage suffers little from pests and diseases in cultivation as long as the soil stays well-drained. Root rot from standing winter water is the biggest risk.

Cabbage white caterpillars occasionally nibble the foliage; check regularly and remove them by hand. Aphids are rare on this lean, windswept plant. Grit, perlite and frost fleece are readily available from garden centres.

Closing

Prostrate cabbage is an unusual, low-growing groundcover for lovers of rock gardens and wall plantings with a Mediterranean character. With an exceptionally well-drained spot and winter protection in colder regions, this rare North African cliff plant forms a dense, yellow-flowering mat. GardenWorld can help you design a rock garden with unusual, drought-tolerant groundcovers. Visit GardenWorld for garden design and the GardenWorld plant database for more species.