Few perennials bloom as profusely as the astilbe even in the shade. For this reason, the perennial from the saxifrage family is extremely valuable for garden design. From a horticultural point of view, the China Astilbe (Astilbe chinensis) and the Arendsii hybrids (Astilbe x arendsii) bred by the German perennial gardener Georg Arends are particularly interesting. Already in the 19th century, the magnificent flower was used as an ornamental plant.
Profile of astilbe:
Scientific name: Spiraea vanhouttei
Plant family: saxifrage family (Saxifragaceae)
Other names: false goat’s beard, false spirea.
Planting time: all year, but no frost, autumn preferred
Flowering period: May to June
Location: sunny to partially shaded
Soil quality: gritty to loamy, moderately dry to moist, moderately nutrient-rich to nutrient-rich
These information are for temperate climate!
Use in: single position, cut hedges, free growing hedges, group planting, visual cover, flower garden, natural garden
Winter hardiness: hardy
Bee and insect friendly: a little
Plant characteristics and classification of astilbe
Plant order, origin and occurrence of astilbe
The astilbe (Spiraea vanhouttei) is a cultivated form of the meadowsweet, which was cultivated by the Billiard nursery in France in the 19th century. Spiraea cantoniensis from China and Spiraea trilobata from Siberia and Northeast Asia are considered parent species. The home of the spireas is in East Asia.
The genus includes about 80 species, the majority of which are native to China. Thanks to its robustness and versatility, it attracted early interest from plant breeders who selected a variety of cultural forms, one of which astilbe is the most popular. Spireas belong to the saxifrage family (Saxifragaceae) and in addition to the spring-flowering representatives, there are also summer-flowering representatives, which mainly form pink flowers. The botanical generic name “Spiraea” can be derived from the Greek word speira, which means twist or wind and refers to the often twisted shape of the fruit.
Characteristics of astilbe
The astilbe quickly grows into a medium-high, deciduous shrub, whose annual growth rates are 20 to 50 centimeters (8 to 20 in). It grows to around two meters high (6.5 ft), rarely higher, and one to two meters (3 to 6.5 ft) wide. The side shoots of the flat-rooted Spiraea vanhouttei initially grow upright, later they hang over in elegant arches.
The shoots of the astilbe are covered with alternately arranged, about 5 cm (2 in) long leaves. Their leaf margins are sawn on the upper half, later they are almost three-lobed. Before they are shed, the leaves turn yellow in autumn.
In May and June, the astilbe develops a lush bloom that looks particularly beautiful on the elegantly overhanging branches. The five-pointed, round white flowers stand together in dense, umbel-like inflorescences, which spread a tart, harsh fragrance. The single flower is only a few millimeters in diameter, but the entire inflorescence can be significantly larger than 10 cm (4 in). Bees and other insects do not visit very often.
The astilbe develops small, inconspicuous follicles.
Astilbe – cultivation and care
The undemanding astilbe thrives both in the sun and in partial shade. The brighter and sunnier your spot is, the richer the flower will be. Spiraea vanhouttei is considered to be moderately air pollution-resistant and is only suitable to a limited extent for inner-city climates.
Astilbe is also considered to be entirely uncomplicated when it comes to soil, because it copes well with dry soils that are poor in nutrients. In addition, Spiraea vanhouttei is lime-tolerant and also tolerates slightly acidic pH values. Only waterlogging should be avoided.
In order to raise second growth from astilbe, you can cut cuttings or live stakes. In spring, cuttings are cut from the shoots, about 15 cm (6 in) long, half-lignified shoot tips and cultivated in pots with growing soil until roots have formed. Live stakes are completely lignified shoots, which are best cut in autumn and then inserted with the right side down into prepared planting holes. In addition, during the growing season from spring to autumn, new plants can be obtained quite easily by layer. As a rule, it takes about a year until sufficient roots have formed and the layer can be separated from the mother plant.
Astilbe is usually offered as container plant and can be planted practically all year round, with the exception of the frost periods. As with many other ornamental shrubs, planting in the autumn has proven itself so that the shrubs have grown well for the coming spring. For a hedge planting, a distance of 35 cm (12 in) between the individual plants is recommended.
The planting hole should be at least twice the size of the root ball. It is best to loosen the soil of the excavated hole with a rake. In the case of heavy soils, you should provide more permeability by placing a layer of gravel in the planting hole. After filling up the soil, it is watered rigorously. A layer of mulch around the root area keeps the moisture in the soil.
Care / Watering / Fertilization
The astilbe does not require any special maintenance. Just after planting, you should make sure that the soil is always well supplied with water.
In order to keep flowering abundant, it is advisable to regularly prune the astilbe and thereby rejuvenate it. Every two to three years you should cut older shoots back to the ground in late autumn or early spring. As an alternative, you can cut back all flowered branches right up to the roots immediately after flowering. Spiraea vanhouttei also tolerates a radical pruning and can be used as a topiary. However, one then deprives oneself of the elegant appearance of their gracefully overhanging flower shoots.
Diseases and pests
In spring, aphids like to appear on the young shoots of the astilbe. Those can easily be sprayed off with a water jet or wiped off with a kitchen towel. In bad weather periods powdery mildew can affect the shoots.
Spiraea vanhouttei is completely hardy and requires no special protective measures.
Use in the garden
As an element of free-growing hedges, astilbe is a very good choice, because it blooms when most of the spring bloomers have already finished flowering. The shrubs, which are extremely well tolerated by prune, can also be raised as topiary hedges, but you should avoid edged and cornered cut patterns and give their contour a soft shape.
Also in groups of three to five plants, it is a striking eye-catcher, especially during its flowering period. If you want to prettify an unused garden corner that is difficult to access, you will find an uncomplicated ally, because it thrives where other shrubs would only wither. Because of its compact growth and manageable size, Spiraea vanhouttei is also suitable for use in small gardens.