Androsace: cultivation, planting, care

Description and Botany

The Androsaces, belonging to the primrose family, are close cousins of primroses. These small alpine plants native to the North-western Himalayas form a rather diverse group. The genus includes around thirty perennial, biennial or annual species, growing in the wild at altitudes of over 4,000 metres, directly on rocks or in scree, dry meadows and rocky areas, accustomed to extreme conditions, like the Alpine Rock Jasmine (Androsace alpina), an endemic species of our Alpine mountains and protected. Among the most cultivated species in our gardens, we find the Androsace sarmentosa, characterised by its silvery rosettes covered in white hairs, the A. septentrionalis, and its cultivar ‘Star Dust’, appreciated for its small white flowers that appear abundantly in spring, like a constellation, or the A. sempervivoides which resembles houseleek, with its thick, fleshy foliage arranged in compact rosettes.

With rather slow growth, androsaces form, depending on the species, small compact tufts, erect or creeping, not exceeding 25 cm in height with a spread of 20 to 30 cm. They spread slowly into low cushions, rooting in the smallest cracks. The foliage offers a beautiful diversity in both shapes and hues. In perennials, it is evergreen, persisting throughout the year, summer and winter alike. It ranges from bluish-green to silvery. It can take the form of almost succulent rosettes, which root upon contact with the soil like houseleeks resembling small artichokes or, conversely, basal lanceolate and dentate leaves.

The foliage of androsaces can take very varied forms depending on the species. Androsace vandellii and Androsace sarmentosa ‘Chumbyi’ (photos: Ghislain118).

The flowers of Androsaces, generally white or pink, sometimes violet, dark red, more rarely yellow, emerge in spring above the foliage. They are sometimes borne on a flower stalk that can reach up to 20 cm in height. Arranged in clusters or umbels, at the top of short stems, they are usually star-shaped and consist of five petals with five well-defined lobes that unfold around a central yellow to red heart. The delicacy of their petals, often slightly fragrant, contrasts with the robustness of the basal leaves.

The shades of white and pink of the flowers vary according to the species, offering a palette of subtle colours. For example, the Androsace septentrionalis ‘Star Dust’ is adorned with small white flowers that seem to float above the silvery rosette, while the Androsace sarmentosa presents small mauve-pink flowers that form a lovely contrast with its silvery foliage.

The flowering of Androsaces is not only a visual delight, it also attracts pollinators such as bees and butterflies.

Androsace hirtella

After flowering, the flowers turn into small dry capsules, which open at ripeness to release the seeds, thus allowing the dispersal and reproduction of the Androsace. The seeds are small and light, adapted to spread in the harsh montane environments where Androsaces thrive.

Main species and varieties

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Planting Androsace

Where to plant Androsace?

A quintessential montane plant, Androsace can withstand harsh climate conditions (down to -25°C) and poor soils. Its adaptation to alpine environments allows it to survive extreme conditions, enduring cold winds and snow. This hardiness makes it particularly suited to rock gardens where conditions can vary. It can even be grown in fairly cold regions. Androsace particularly dislikes overly wet soils in winter and heavy soils that retain water and cause root rot, as well as heatwaves and excessively dry situations in summer. Therefore, if you live in a rainy region, it may need winter protection from rain and stagnant moisture.

Androsace requires well-drained soil to avoid excess moisture, which could be fatal. A mix of compost, sand and gravel is ideal to mimic its natural rocky habitat. It thrives best in soil that remains cool, and appreciates limestone and stony soils. This perennial will settle best in rockeries that aren’t too dry, not being the most adapted to arid conditions. Ordinary soil arranged between large stones is perfect. It prefers sunny or lightly shaded positions, especially in warmer regions, to avoid excessive drying in summer.

Androsace is particularly suited to rock gardens due to its ability to grow in challenging conditions and well-drained soils. Its compact habit and leaf rosettes form dense mats that elegantly fill gaps between stones. It also works well in raised beds, atop walls or on slopes. But beware, it spreads via long stolons and dislikes root competition.

Its preferred habitat of stony, well-drained soils makes it perfect for creating miniature rockeries reminiscent of alpine slopes.

Androsace alpina (photo: John Game)

When to plant?

You can plant Androsace in early spring, from March to April, or in autumn, from September to November. Avoid frost periods.

How to plant Androsace?

When planting, ensure you prepare a well-drained soil mix by adding gravel or sand. Limestone and stony soil is ideal as it replicates its natural montane habitat conditions. You can position it between stones to create a favourable microclimate and provide extra protection against excessive moisture. If your soil is naturally heavy or clayey, add more sand and gravel to improve permeability.

• Dig a hole three times wider than the root ball
• Plant the Androsace without burying the collar
• Space each young plant 40cm apart to avoid competition
• Backfill with excavated soil, then firm gently
• Water thoroughly

Continue watering regularly to ensure establishment.

Care and maintenance

Extremely undemanding, the Androsace grows on its own, without maintenance, and does not require watering once well-rooted. It needs regular watering at the start of cultivation, after which it will no longer be necessary, except during drought periods, but avoid excess moisture. Remove faded inflorescences, and damaged or dried rosettes from time to time. Clear weeds around the base to reduce competition from other plants.

Every two or three years, divide the clumps to rejuvenate them.

In terms of diseases, the Androsace only fears those related to excess moisture. It is therefore important to plant it in well-draining substrate. If you live in a rainy region, it is best to create a bed of gravel or stones around the rosettes to prevent water from stagnating and causing rot. The pubescent varieties, such as Androsace sarmentosa, are more sensitive than others to winter moisture.

Propagation

Dividing clumps in spring, on well-established plants, remains the simplest and quickest method to propagate Androsace.

• Lift the rootball with a small hand trowel or transplanter.
• Using a sharp knife, separate small clump divisions, ensuring each section has several rosettes and a good portion of attached stolons.
• Replant these divisions immediately in the garden or in pots, using a well-draining substrate.
• Water lightly.

Garden companions

Androsaces are essential in alpine gardens where they form beautiful tapetum all year round in borders, on walls or in rockeries. You can easily plant them with other alpine plants and rockery perennials that are not too vigorous and appreciate well-draining substrates. Saxifrages, with their dense foliage and small star-shaped flowers, are excellent companions for Androsace. Gentians, with their intense blue flowers, share with Androsace a preference for calcareous, well-drained soil as well as good hardiness. With its tolerance to harsh conditions, Edelweiss is a perfect partner, as are Pasque flowers, Alpine erinus, Wall bellflowers and Rock roses.

In borders, consider ground-covering Sedums, Houseleeks, Storksbills, Sea thrift, or Thyme, spacing them adequately to avoid overcrowding.

Pair Androsace with other small alpine perennials! Androsace helvetica (photo: Ghislain118), Draba aizoides (photo: Björn S.), Gentiana acaulis, Erinus alpinus ‘Dr Hälne’ and Sempervivum arachnoideum.