Arenaria, Sandwort: planting, cultivation, maintenance

Description and Botany

The genus Arenaria belongs to the Caryophyllaceae family, alongside the Carnation, Gypsophila, Silene, and Soapwort. Primarily native to the Northern Hemisphere, it can be found globally, in both cold mountainous regions and more temperate areas. The Arenaria, or Sabline, derives its vernacular name from its preference for well-draining sandy soils. Etymologically, the word ‘Arena’ also refers to sand. The genus comprises around 160 species of perennial and annual plants, but only a few are used for ornamental purposes. Among them, the most common are Arenaria montana (Mountain Sabline), Arenaria pungens (Silver Sagine), Arenaria balearica (Balearic Sabline), and Arenaria tetraquetra (syn. Arenaria pyrenaica, or Four-ranked Sabline).

This perennial can sometimes appear shrubby with age and under certain growing conditions, but it predominantly remains a spreading groundcover plant that forms low cushions. Growing to a height of 10 to 15 centimetres, the stump features fine rooting stems that, like those of the Fragrant Violet, creep along the soil surface. The Sabline thus spreads over approximately forty centimetres.

Arenaria montana – Botanical illustration (source Biodiversity Heritage Library – Flickr)

The persistent foliage consists of tiny, slightly villous leaves, green to grey-green, which can sometimes resemble moss. In Arenaria tetraquetra, the leaves overlap curiously, giving it a false resemblance to heather. From this dense cushion, small flowers with five petals emerge from spring to summer, appearing solitary or in clusters atop short upright stems, and they are most often white with a yellow-green eye. Measuring a few millimetres in Arenaria balearica, they can reach up to 2.5 centimetres for the Mountain Sabline, which, proportionally, displays the widest corollas. The flowering period is long and can extend over a month. Some species bear purple flowers, such as the Red Sabline (Arenaria rubra), an annual used in herbalism for its diuretic properties; nicknamed ‘stonebreaker’, it is indeed used in decoction or infusion to dissolve kidney stones. Once the flowers have faded, the Arenaria produces tiny capsule fruits.

The foliage of Arenaria varies greatly by species: Arenaria tetraquetra ssp granatensis (photo Ghislain118), Arenaria montana (photo Mtiffany71 – Wikimedia) and Arenaria pungens (photo Römert – Wikimedia)

Extremely floriferous and hardy (-15°C and beyond), Arenaria is a perennial very easy to grow and disease-free. Its origins make it suitable for a sunny to partially shaded location, in any cool but well-drained soil. It is thus perfect for enhancing a cool rockery, greening a not-too-dry wall, adorning the front of borders, or decorating the gaps between paving stones and slabs. It is also a good candidate for pot displays or flowering troughs. However, be cautious, as its chances of survival are low in overly dry conditions.

Arenaria montana (photo Kenraiz – Wikimedia) and Arenaria rubra (photo AnRo0002 – Wikimedia)

The different species

Arenaria montana

The Mountain Sandwort forms a persistent grey-green cushion, which is covered in white flowers from late spring to early summer. A hardy and low-maintenance rock garden plant!

• Flowering time June to August
• Height at maturity 15 cm

See the full description

Arenaria tetraquetra subsp. amabilis subsp. Amabilis

The curious imbricate foliage of the Four-ranked Sandwort is original and decorative. A well-manicured groundcover adorned with white flowers.

• Flowering time June, July
• Height at maturity 10 cm

See the full description

Arenaria tetraquetra subsp. granatensis subsp. granatensis

A variety of Four-ranked Sandwort, which forms dense carpets covered in white flowers.

• Flowering time May
• Height at maturity 10 cm

See the full description

Planting

Where to Plant the Sandwort

Arenaria is a mountain plant. It is hardy and suitable for many gardens. As it does not tolerate very dry and hot conditions well, ensure it has a bright location. In the North, it can be placed in a sunny spot; further South, partial shade is more suitable. In all cases, soil that retains good moisture during the season but does not allow water to stagnate is key to success. It accepts all types of soil that are not too rich or too calcareous.

The Sandwort is one of those alpine perennials that thrive in cool rockeries. It can also adorn a low wall, decorate a border of flower beds, or weave between the paving stones of a path to soften its mineral aspect. For gardeners with only a balcony or terrace, pot cultivation yields excellent results. Allow it enough space to develop well, avoiding excessive root competition with potential neighbours.

Arenaria montana – Szeged Botanical Garden (photo Kenraiz – Wikimedia)

When to Plant the Sandwort?

In regions with cold, damp winters, prefer early spring for planting your Sandwort. In milder climates, you can also consider planting it in the early autumn.

How to Plant the Sandwort?

1. Dig a hole 2 to 3 times the size of the root ball and loosen the soil.
2. In heavy soil, improve drainage by adding coarse sand, gravel, or pumice.
3. After thoroughly soaking the root ball by allowing it to absorb water in a bucket while you prepare the soil, place your plant in the desired location.
4. Fill in with the remaining substrate and lightly firm it down.
5. Water generously to ensure good contact between the soil and the roots.
6. Mulch, preferably with a mineral mulch (gravel, sand, etc.), to prevent water from stagnating at the collar (the junction between the aerial and underground parts).
7. Remember to keep the soil moist but not waterlogged during the first few months. Adjust your interventions according to climatic conditions.

In pots, place a drainage layer at the bottom of the container (gravel, clay balls, etc.), and use a light, well-draining substrate that is not too rich, such as potting soil mixed with coarse sand.

Maintenance

The Arenaria is a perennial that requires very little maintenance, especially if you have planted it in well-draining, cool soil, and in a not too arid situation. Occasional watering may be necessary if rainfall is insufficient, but be careful not to drown your plant. Wait until the substrate dries slightly before intervening. An excess of water can indeed cause the roots to rot.

Once the flowering is over, and although pruning is optional, you can cut the plant back quite severely to maintain a dense and compact habit. It will then produce fresh foliage, which remains decorative for the rest of the year.

Multiplication

The simplest method to multiply Arenaria is clump division, which should be done in early spring.

1. Using a spade, lift the plant from the ground, ensuring to retain as many roots and as much soil as possible.
2. Divide your plant into several sections, either by cutting it with your spade or using a sharp knife.
3. Replant immediately the sections obtained in the chosen location.
4. Water and mulch.

Associate Arenaria with the garden

Hardy alpine perennial, Arenaria allows for the creation of low, bright carpets that beautifully punctuate a rockery.

Pair it with other perennials for well-drained soil, such as Saxifrages, Aubriètes, Alysses, Arabis, or even subulate Sagines. Columbines add beautiful, natural colour accents that rhythmically enhance the bed, just like the Mountain Cornflower, with its very dark, almost black corollas, ensuring striking contrasts. The blue of the Asclepias Gentian adds depth, though it is somewhat more demanding in cultivation. The Edelweiss transports you to the steep slopes of the Alps, distinguished by its originality and rarity.

In late winter and early spring, many early-flowering bulbs (Crocus, Chionodoxa, Cyclamen coum, Daffodils, and botanical Tulips…) awaken the scene with cheerfulness.

The Arenaria can also create a setting for taller, upright perennials, such as the Caucasian Speedwell or the tall White Willowherb.

It can also form a carpet against which the structural silhouettes of bushes stand out. Among the rockery conifers, the Japanese Pine, with its upright silhouette, or the Mughus Mountain Pine, with a more compact habit, make excellent candidates. You can also consider deciduous plants such as Abelias and Ceanothus (in not too cold climates), Berberis, Heathers, or certain Cotoneasters.

Finally, to bring grace and movement, focus on grasses. Deciduous or evergreen, they undulate in the wind and energise your compositions.

Arenaria montana, alongside ground-cover plants like Arabis caucasica ‘Roselite’ and Aubrieta x cultorum ‘Novalis Blue’, as well as upright perennials like Columbines and Mountain Centaury