Chrysogonum : planting, cultivation, maintenance

Description and Botany

Chrysogonum, also known as “Golden knee,” is a perennial groundcover plant belonging to the Asteraceae family, much like daisies, asters, or sunflowers. The genus comprises only one species, Chrysogonum virginianum, native to the fresh woodlands of the eastern United States. It has given rise to a few varieties and a more compact, widely cultivated cultivar, ‘André Viette’.

Chrysogonum virginianum, botanical plate, circa 1925

This creeping and stoloniferous perennial plant spreads to form a dense groundcover thanks to its long underground rootstocks. They take root to create a more or less compact vegetative mat, 25-30 cm in height, spreading at least 40-50 cm. Chrysogonum spreads slowly without ever becoming invasive. This carpet-forming clump, taller than it is wide, is deciduous, disappearing with the cold and reappearing in spring.

The reddish-green aerial stems, short and upright, are hairy and highly branched. They bear prominent nodes from which the pedicels emerge, their shape reminiscent of a knee, hence the nickname ‘Golden knee’ given to the plant.

They develop small deciduous leaves, bright green in colour, opposite, oblong, 3 to 10 cm long. Hairy and slightly crinkled, with crenate or dentate margins and prominent veins, they resemble those of the lemon balm in our gardens.

With its slightly hairy texture, this foliage serves as a backdrop to the generous flowering of Chrysogonum. It begins in May and continues uninterrupted until the first frosts. Star-shaped flowers in solitary heads emerge from this verdant mass, in the axils of the upper leaves. They bloom as pure yellow daisies, 2 to 4 cm in diameter. They consist of a row of five broad, rounded florets radiating around a central disc with more or less visible yellow pistils. They have a plicate appearance and are slightly fringed at their tips.

These sun-kissed flowers later produce seeds that self-sow easily, ensuring the plant’s longevity and allowing it to naturalise in the garden.

Chrysogonum flowers and foliage

Species and varieties

Chrysogonum virginianum André Viette

This cultivar is a more compact and floriferous form than the type. A boon for cool rockeries, the edges of water points or light and cool woodland areas.

• Flowering time June to December
• Height at maturity 25 cm

See the product sheet

Chrysogonum virginianum

This is the type species with its endless flowering from late spring until autumn, without interruption. Easy to grow in cool soil, in light shade.

• Flowering time June to December
• Height at maturity 30 cm

See the product sheet

Planting Chrysogonum

Where to Plant It?

A bit slow to establish, the Chrysogonum needs about two years to fully flourish, although flowering occurs as early as the first year of cultivation. Over time, it forms small, very floriferous clumps. Perfectly hardy (down to -23°C), it thrives in most gardens across our regions. Preferring moist soils over arid lands and intolerant of water shortages, it does not appreciate very dry summers, making cultivation tricky in Mediterranean climates.

Regarding soil, it adapts to any light, well-draining, and humus-bearing soil, even peaty, retaining freshness and moisture, especially in summer. Highly adaptable, once well-rooted, it can tolerate occasionally waterlogged or episodically dry soil.

In a location with non-scorching sun or light shade, and cool in summer, it will form clumps that expand over time but remain easy to control. It can also thrive in denser shade. Fearing root competition, avoid planting it at the base of trees and bushes.

Non-invasive, take advantage of its unique qualities as a ground cover to enhance a cool, shaded rockery, a pathway border, a shady slope, the edges of a water feature, to fringe a perennial bed, or brighten a light woodland edge. It’s an excellent plant for beautifying the north-facing side of a house. It also proves useful for covering the base of a rose bush.

When to Plant It?

Planting takes place in spring from February to April or in autumn from September to November, avoiding frost and extreme heat periods.

How to Plant It?

Space the young plants about 40 cm apart and allow for 5 plants per square metre to create a lush ground cover. Add gravel to improve drainage if necessary.

• Dig a planting hole 2 to 3 times wider than the root ball
• Place the plant in the centre of the hole
• Fill with a mix of good potting soil, garden soil, and a handful of compost
• Firm the soil
• Water regularly to encourage establishment

→ Check out our tips for planting a perennial correctly!

Chrysogonum virginianum and Stachys thunbergii (© Peganum)

Maintenance and Care

Hardy and vigorous, the Chrysogonum virginianum requires almost no care once well established.

It prefers a soil that does not dry out too much in summer. It needs sufficient moisture at the base, especially in summer or if rainfall is scarce. Ensure regular watering during the first year of cultivation, then 1 to 2 times a week during hot spells. It can tolerate temporary drought once well rooted. A mulch (straw, leaves, etc.) spread over the stump to limit evaporation will help.

If your soil is poor, a spring application of compost at its base will be beneficial.

Remove faded flowers to encourage the development of new ones.

In autumn or late winter, pull out excess leafy stolons to control the plant’s spread. Divide clumps every 2-3 years to keep them vigorous.

The Chrysogonum virginianum is never diseased and is immune to parasitic attacks. However, in spring, follow our advice to protect its young foliage from slugs and snails.

Multiplication

The Chrysogonum naturalises easily thanks to its underground rootstocks and self-sowing. If you have harvested its seeds at ripeness, you can sow them in buckets or trays in spring, placing them under a cold frame. Dividing the clumps in spring before flowering or in early autumn is simpler to achieve. To propagate it, you can also simply separate the stolons and replant them immediately in the garden in moist soil.

Division

• With a garden fork, lift a portion of the stump
• Divide it into several sections, each with roots and the beginnings of leaves
• Replant immediately in the ground and monitor watering to ensure successful establishment

Associate

The Chrysogonum virginianum is an interesting ground cover to brighten up the cool, shaded areas of a garden with its long, sunny flowering. It pairs well with perennials that thrive in cool soil and partial shade. It fits effortlessly into a natural garden or water gardens.

It thrives in cool but not waterlogged soil along the edges of ponds or water features, alongside the Ligularia dentata ‘Dark Beauty’ with its yellow-orange flowers and the Carex elata ‘Aurea’ for a very luminous composition.

Arums, hostas, meadowsweets, Virginia bluebells, and hardy geraniums such as the hardy geranium ‘Bob’s Blunder’ and the hardy geranium ‘Gravetye’ will also make excellent companions.

A cool-soil association featuring Chrysogonum, Tradescantia, a Ligularia dentata, and some beautiful hostas

It can also accompany summer flowers in non-scorching sunlight, provided the soil remains cool. It can be used to fill gaps in a perennial border alongside Knautia, masterworts, or blue Phlox such as the Phlox divaricata ‘Chattahoochee’. It can also adorn the base of roses alongside other ground cover perennials, such as Heucheras like the Heucherella ‘Stoplight’ with its yellow to lime-green foliage and creeping Bugles.

→ Discover more ideas for pairing with Chrysogonum with Virginie’s tips!