Horticulture/Solidago

The goldenrods (Solidago spp.) are members of a genus of plants in the famile ../Asteraceae/, native to North America. They are commonly found as wildflowers in their native range, but some are also grown as garden plants. Some species are also rather serious invasives in other parts of the world.

About 80 perennial species make up the genus Solidago, most being found in the meadows and pastures, along roads, ditches and waste areas in North America, and a few have naturalised in Europe.

The different species are difficult to distinguish. Probably due to their bright, golden yellow flower heads blooming in late summer, the goldenrod is often unfairly blamed for causing hay fever in humans. The pollen causing these allergy problems is mainly produced by ../Ambrosia/ (Ragweed), which blooms at the same time as the goldenrods, but the goldenrod pollen is too heavy and sticky to be blown far from the flowers.

Description
They have slender stems, usually hairless but S. canadensis shows hairs on the upper stem. They can grow to a length between 60 cm and 1.5 m. The leaves are alternate, simple, and linear to lanceolate. Their margins are usually finely to sharply serrated. Flowers are small heads borne in large showy inflorescences.

Growing conditions
The only common thread among the various species of goldenrods is that they require full sun. Otherwise, they are naturally found everywhere from road cuts to wetlands, and everywhere in between. Some species will "flop" if growing in overly fertile soils.

Varieties

 * A hybrid with aster, known as x Solidaster is less unruly, with pale yellow flowers, equally suitable for dried arrangements.
 * Solidago canadensis was introduced as a garden plant in Central Europe, and is now common in the wild. In Germany, it is considered an invasive species that displaces native vegetation from its natural habitat.

Uses
In the garden, goldenrods are grown for their showy yellow blooms borne from midsummer to late autumn, depending on the species. Most plants are too coarse for garden use, but many cultivars have been selected for dwarf size and finer foliage.

Goldenrods bloom in late summer and early fall and some species produce abundant nectar when moisture is plentiful before bloom, and the bloom period is relatively warm and sunny. Honey from goldenrods often is dark and strong due to admixtures of other nectars. However when there is a strong honey flow, a light (often water white), spicy-tasting Monofloral honey|honey is produced. While the bees are ripening the honey there is a rank odor and taste, but finished honey is much milder.

Goldenrods are a preferred food of the monarch butterfly during their fall migration southward, and can be planted to attract them.

Propagation
Goldenrods divide easily, and can become weedy if allowed to go to seed.

Caution should be taken when planting goldenrods because they are allelopathic, and can kill neighboring plants. One species, Solidago canadensis, is invasive in Germany and China, in part due to its allelopathic trait.