In nature, all plants do not have the same cultural needs and so much the better! Saxicolous plants like to grow on rocks, slabs, dry stone walls. No need for soil, nor astronomic quantities of water for them to grow happily. Discovery...
What is a Saxicolous plant?
The etymology of the word 'saxicole' helps us to see more clearly. Saxum' in Latin means 'rock', it is followed by the suffix 'cole' which means 'to cultivate', 'to live'. Saxicolous plants grow on a mineral element only.
There are other Saxicolous organisms such as certain algae, lichens (symbiosis between fungi and algae) and even bacteria.
Saxicolous plants do not need soil to live since their growth medium is mineral, they cling to it thanks to filaments (rhizoids) which do not have a nutrient absorption function as the roots of conventional plants would do. This fixation system appeared a very long time ago on the evolutionary scale, about 400 million years ago. These plants take up water and nutrients from the atmosphere to feed, or even become carnivorous to compensate for the lack of food (Pinguicula gypsicola).
The terms 'Rupicole' or 'Lithophytes' also define these plants adapted and growing directly on a mineral support.
The true saxicolous plants are usually mosses or ferns such as Asplenium certerach or Pyrrosia rupestris. They should not be confused with the chasmophyte plants which develop in the slightest crevice or the smallest crack and which have roots sometimes very extensive in order to be able to draw water and nutrient resources and to cling as well as possible to the elements. Their characteristics are that they are generally low to best resist wind, lack of water and heat. Their seeds are often very small to be able to slip into their preferred environment or to be brought there by small animals, they have a strong germinating power and do not require too much moisture or a large quantity of soil.
Among these plants we find the 'Navel of Venus' (Umbilicus rupestris), but also houselegs, saxifrages or cymbalaria.
Wall plants, simplicity and ease of cultivation
In the garden, the true Saxicolian plants usually establish themselves on the rock faces over time. Mosses, lichens or small ferns then offer their naturally ornamental silhouettes without having planted or maintained them.
Other plants can adapt to the lack of soil and the specific life between stones, large rocks or cracks. They can be used between the slabs of a terrace, to decorate Japanese steps, or to dress a staircase or a dry stone wall.
- The cymbalaria muralis (Cymbalaria muralis) forms tufts with frank green foliage and is covered with small lilac flowers from June to November. Very rustic, it finds its place in all walls exposed to half-shade.
- The various species of saxifrages (Saxifraga) are very numerous since there are more than 400 different species. Rupicolous, they colonize the cracks or interstices between rocks, which earned them their vernacular name of 'Stone breaker'. Among all these species, the moss saxifrages are ideal to dress the areas between Japanese steps or slabs but also in troughs or rocks. The evergreen foliage forms rounded tufts from which emerge white, pink or red flowers from May to August. These plants appreciate the half-shade and a substrate always fresh. They can be envisaged in mountainous zones because it resists to -30°C.
- The Japanese saxifrages (Saxifraga fortunei) and their numerous cultivars flower at the end of the season, from September to December. Black Ruby' with its black foliage and fuchsia-pink flowers will be noticed, as will 'Crystal Pink' with its variegated pink, white and green leaves.
- The houseleek (Sempervivum) is one of the plants recommended to the novice gardener as they are so robust. They resist everything and do not require anything to grow as long as the substrate is well drained. These succulent plants form rosettes of tightly packed leaves. They produce crawling runners covering over time the riprap. In summer star-shaped flowers appear at the end of a long stem. Yellow, cream, red or pink, they always make their effect. These plants are ideal on a vegetated roof, but also in the crevices of low walls or along driveways. Sempervivum arachnoideum is very appreciated for its leaves covered with white crossed silks resembling spider webs, while 'Congo' has orange rosettes almost red, very useful in mosaiculture.
- The small sedums also make the happiness of the gardener wishing to dress a mineral zone. There is something for everyone! Sedum dasyphyllum unfolds a multitude of tiny blue rosettes between the stones. It decorates marvelously the anfractuosities of the dry stone walls, likes rocks and troughs. In summer it produces small white flowers that are very appreciated by pollinating insects. Sedum acre or 'wall pepper' is one of the most famous species. The glaucous green foliage disappears under an avalanche of bright yellow stars in summer. You can have fun collecting sedums, so many varieties are available and use them wherever the mineral space is in majority!
- The Arabis (Arabis) is particularly popular in sunny gardens in mountainous areas. Its very fragrant pink or white flowers form real cushions in low walls or between slabs but also in rock gardens.
- The alyssum with its delicious honey scent attracts pollinating insects from June to October. It is ideally planted in a low wall near the vegetable garden or orchard. Very hardy, resistant to drought, full sun and wind, this very flowering plant also finds its place in borders of flowerbeds, in paving or to brighten the crevices of a natural staircase.
- The wall bellflower (Campanula muralis) grows on its own between the large rocks bringing the bluish or mauve touch of its elegant bells in all simplicity from May to August. Rustic, robust and flowering, it is a perfect subject to decorate a dry stone wall but also rock gardens or flowering troughs.
- For the same uses, think of the aubriète which is covered with purple or pink flowers from March to June. This very resistant plant appreciates a rather calcareous substrate and the full sun. Rugging, slightly falling down, it is ideal planted in flowered walls.
