Perennial knawel
Scleranthus perennis · Caryophyllaceae
The gardener's calendar
Ideal time to plant perennial knawel: set it out when the soil is neither frozen nor waterlogged, and water generously as it establishes.
ID card
- Family
- Caryophyllaceae
- Form
- Perennial herb
- Foliage
- Evergreen, fine and linear
- Flowering
- Summer (June to August)
- Mature size
- 4–8 inches tall, 6–12 inches spread
- Hardiness
- Very hardy (down to 5 °F)
- Origin
- Central and southern Europe
- Growth
- Slow to moderate
Care
Light and climate
Perennial sclera requires a sunny, well-ventilated position. It tolerates dry and hot exposures well. Avoid dense shade, which slows growth and encourages rot.
Soil and drainage
This plant demands very well-drained, light and poor soil, ideally sandy or gravelly. Excess moisture or rich soil compromises its longevity. Amend with sand or gravel if your soil is too compact.
Watering
Once established, perennial sclera is very drought-tolerant. Water moderately during the growing season, only when the soil surface is dry. In winter, drastically reduce watering to prevent root rot.
Pruning and maintenance
Low-maintenance, this plant mainly needs preventive care: remove dead or rotted parts in late winter. You can cut it back lightly after flowering to maintain a compact shape.
Feeding
Perennial sclera prefers poor soils and needs virtually no fertilizer. A very light feeding in spring (diluted balanced fertilizer) is plenty; too many nutrients encourage legginess.
Pests and diseases
Very resistant, it mainly fears excess moisture, which causes crown and root rot. Ensure impeccable drainage and good air circulation to prevent fungal problems.
Did you know?
Perennial sclera is a relic of ancient heathlands and calcareous grasslands in Europe. Once very common, it has disappeared from many regions with intensive agriculture and urbanization, making it today a plant of botanical interest and conversation for lovers of minimalist and ecological gardens.
Where to buy it
Plant in spring or early autumn, avoiding spells of intense heat. Pick a plant with healthy foliage and roots that are not exposed. Best time: March, April, May, September.
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Tips generated and checked by Viridia — adapt them to your local climate.