Description
Astilbe × arendsii is a perennial of the saxifrage family. Many hybrids are grown. The plants reach 50–150 cm, with straight, stiff stems and doubly pinnate leaves whose edges are doubly toothed and whose blades are wrinkled and roughly hairy.
Depending on the variety, astilbes flower from mid-June to September. The small flowers are white, pink, lilac-red and carmine, gathered in spikes. The plumes at the tips of the stems are usually upright, with only the lower branches drooping slightly. Depending on their flowering time, astilbe varieties are divided into early, mid-season and late.
It is used in groups in shady, moist places in parks and gardens, together with hostas, ferns and meadowsweets. It is also grown as a cut flower outdoors and under forcing.
Requirements
Astilbes need fertile, deeply cultivated and moist soil. A partially shaded position by the edges of ponds is ideal. The wetter the soil, the less full sun harms the plants. They are sensitive to spring frosts.
Propagation
They are propagated by dividing 8–10-year-old plants in late autumn, less often in spring. Each division must have a piece of rhizome, adventitious roots and visible buds. Plant them 10 cm deep in trays of peat compost or light, sandy soil, and then move the trays to a cold frame. After generous watering cover everything with moss or conifer needles. Remove the covering in spring before the shoots appear. The plants are planted out in their final position in spring or autumn of the following year, 50 x 25 cm apart.
Care
Astilbes do not like mineral fertilisers, but from the second year of cultivation spread well-rotted manure or a peat-and-manure compost between the plants before the shoots appear. On less moist soils, generous watering is essential from the time the shoots appear until flowering. They need covering in winter. For forcing, the plants are prepared in early autumn. Clumps with at least 6 clearly visible buds are planted in pots 17–20 cm across and kept in a cold frame at 0–1.5°C, plunged in moist peat. When the frosts come, they are additionally protected with peat, leaves and spruce branches. Forcing starts in February. At first the temperature should be 10–12°C; once the leaves appear it is raised to 15–18°C and the greenhouse is shaded. The plants are only misted and watered, not fed. Astilbes forced from February flower after 10–12 weeks; those forced at the end of April or beginning of May flower after just 3–4 weeks.