Stone herbs, Alyssum – varieties, care and wintering

Alyssum is a low aromatic plant mostly used for rock gardens and planters. The perennial, bushy, spreading plant originating from the Canary Islands can be recognized by its numerous small, round flower heads. Depending on the variety, these look white, pink, purple and violet. All varieties have a slightly sweet, honey-like and sometimes quite strong scent. Alyssum is very undemanding and easy to care for and forms dense cushions, especially through self-sowing. The plants rarely grow higher than 15 cm and if they do, the shoots fall over and lie rather than stand. In hanging vessels, the flowers then hang nicely over the edge.

• Location – sunny to semi-shady, great rock garden plant, ideal as a traffic light plant
• Plant substrate – well-drained soil, containing humus, moderately nutritious, preferably also calcareous, the plants actually grow in almost any garden soil, standard soil is sufficient for keeping containers
• Plants – outdoors from the end of May, planting distance 20 cm, good partners: horned violets, male fidelity and low autumn asters, transplant stocks in spring or autumn
• Watering – in severe drought, especially in container culture, it usually survives longer periods of drought without any problems, wet is much worse
• Fertilize – is not required. If there are too many nutrients, the plant will produce a lot of foliage but hardly any flowers. Only fertilize lightly after pruning
• Pruning – Pruning back in summer to encourage a second bloom, then fertilize lightly
• Overwintering – conditionally hardy, but self-sowing it is site-faithful, the plants themselves only tolerate a little frost, the seeds significantly more
• Propagation – Sow indoors from mid-March, prick out in small groups of about 6 plants in a container. Sow directly outdoors from April. Likes to self-seed, even in the smallest cracks and between flagstones
• Diseases – very healthy and robust plant, diseases are not known
• Pests – snails, especially in wet weather and especially young plants are affected, spread slug pellets

Rock Alyssum (Alyssum saxatile)

The rock alyssum is particularly noticeable because of its bright yellow flowers, which can be seen in large numbers. They have enormous luminosity. The flowering lasts from April to May. The flowers are on long stalks. The grey-green leaves are also decorative. The plants grow to a height of about 40 cm, but often fall over and continue to grow lying down. The rock alyssum thrives best in the rocky steppe or in similar places in the garden. It is well suited for stone joints or for stone systems. With its evergreen foliage, this alyssum is an eye-catcher even in the gray season.

• Location – sunny to off-sun, at least 4 hours of sun, but more hours are favorable, stone herbs all like the sun and can also cope with the midday sun
• Plant substrate – dry and permeable, likes a little sandy, ideal for a drying bed or the rock garden, never permanently wet
• Plants – can be planted at any time, except in frost, planting distance about 30 cm to 40 cm, forms pillow-like cushions,
• Watering – water regularly until growth (6 months), later tolerates drought quite well, water with long-lasting heat
• Fertilize – with pond water or compost, not too many nutrients, otherwise the energy goes into leaf growth instead of flowering
• Pruning – right after flowering to keep the plant in shape. It also prevents powdery mildew.
• Overwintering – hardy to about -20°C, does not need shelter
• Multiply – sowing, division
• Diseases – mainly due to care errors, for example permanent wetness, root rot, otherwise the plants are rather robust and healthy and not so easy to kill
• Pests – are not known, which of course does not mean that aphids or similar insects cannot occur

Berg-Steinkraut (Alyssum montanum)

Mountain Alyssum occurs naturally in Central Europe. There are also some stocks in Germany, but not many. This Alyssum is not as flashy as the varieties described above, but it also has a quiet charm. It doesn’t form those dense cushions and doesn’t have the luminosity of the buds, even if they’re yellow. The leaves are grey-green. The densely hairy, prostrate shoots and the needle-shaped leaves are striking. Flowering begins in April and lasts until about the end of May. The flowers are only slightly scented. The plants are 10 to 20 cm high and are evergreen.
The mountain stone herb is one of the protected species in Germany: under no circumstances should it be taken from the wild and planted in the garden. The most commonly offered variety is ‘Berggold’.

• Location – sunny, quiet full sun, the more the better, very heat tolerant, needs warmth, in stone joints, on top of walls, in stone structures, green roofs
• Plant substrate – dry, permeable soil, pH value – neutral, low in nutrients, likes lime in the soil, must not be acidic, sandy, gravelly, with gravel or stone chippings, no compacted soil
• Planting – planting distance 30 to 40 cm, plant in tuffs
• Watering – hardly needs to be watered, handles dryness well, but not at all with permanent wetness
• Fertilize – do not fertilize, if there are too many nutrients, the plants often become lazy
• Pruning – cut the shoots in half after flowering, this ensures re-blooming in September, protects against mildew and keeps the plants compact
• Hibernate – sufficiently frost hardy, even without protection
• Propagation – sow in autumn or spring, cold germs, ensure cold treatment, use seed soil with a third of sand, cover only lightly with soil, keep evenly moist, cuttings in summer (use rooting hormone)
• Diseases – the plants are very robust and healthy and hardly susceptible to diseases. Only wetness is harmful, as root rot quickly occurs. Compacted soil does not cause diseases, but the plants cannot develop and simply die.
• Pests – typical pests are not known, which does not mean that the plants are never infested. Aphids can also be found here, but are easily eliminated by rinsing. Caterpillars and snails especially eat young shoots.

Chalice Alyssum (Alyssum alyssoides)

The calyx stone herb is one of the annual plants and is only distributed in certain areas in Central Europe. There are also occurrences in Germany. The plants like quarries, calcareous grassland, sandy fallow land and warm, open soil. The plants have a significantly longer flowering period than other species, namely from April to September. Another peculiarity is that the flowers are self-pollinating. The seeds are spread by the wind. The Chalice Alyssum is 5 to 20 cm high and grows upright or ascending and mostly branches from the ground up. The flowers are pale yellow, white at the end and very small.

• Site – dry grassland, warm and sunny, stone surfaces in full sun, also on the edge of trees
• Plant substrate – permeable and often calcareous soil, poor in nutrients, dry
• Planting – best planted in small tuffs
• Watering – tolerates drought well, only water in the event of prolonged drought, too much water is harmful
• Fertilize – do not fertilize, too many nutrients are rather disadvantageous, the plants are very frugal. Too many nutrients lead to leaf growth and few flowers
• Pruning – prune back after flowering to prevent shoots from falling apart and plants to flower again. In addition, mildew is prevented
• Hibernation – actually hardy, but the plants often do not survive due to the wetness in winter, but they always come back through self-sowing
• Propagating – Sowing, often by self-seeding
• Diseases – powdery mildew, in high heat and drought, otherwise very hardy and healthy
• Pests – rare, but not impossible, caterpillars and snails love the plants, but snails do not make good progress as the year progresses due to the drought

Frequently Asked Questions

Are stone herbs also suitable for balcony boxes?
Yes, especially the species that don’t grow so upright, but rather lying down. These then hang down nicely, which is particularly good for hanging baskets or the fronts of balcony boxes. It is important that you only put plants together in a container that have the same requirements for soil, sun, watering and fertilizing. Many balcony and potted plants have to be supplied with plenty of water in summer and also need regular fertilizer in order to be able to develop and open their flowers. These then do not go well with stone herbs, which do not like it so moist and rather low in nutrients.

Fragrance stone rich is often listed under a different name. Now which one is correct?
Scented rock, commonly referred to as stone herb par excellence, used to have the Latin name Alyssum maritima. Today it is called Lobularia maritima. However, this is very often stated incorrectly, because of course habit sometimes triumphs over the new designation. Both names are often given to be on the safe side.