Twin Arnica Plant Care

Twin Arnica (Arnica sororia) belongs to the Asteraceae family within the Arnica genus. Twin Arnica is native to Western Canada and the Western United States. Twin Arnica is also known as Sister Arnica, Arnica fulgens.

Twin Arnica displays a low rosette, clumping growth habit, reaching up to 1.5 ft tall with a spread of approximately 1 ft. Twin Arnica produces bright yellow daisy-like flowers.

Leaf size: approximately 4 inches.

Water a young or newly planted Twin Arnica every 7–10 days, soaking the whole root zone, until it is established — usually one to two growing seasons. Established shrubs mainly need water during long dry spells. In a container, water whenever the top few centimetres of soil are dry.

Twin Arnica thrives in full sun to partial shade.

Arnica sororia tolerates temperatures of 60–75°F. Twin Arnica prefers humidity levels of 40–60%.

Well-draining, loamy soil with good organic content. Good drainage is essential for Twin Arnica to prevent waterlogging, which leads to root rot and fungal issues.

Feed Twin Arnica every 6 months during the growing season with a balanced, slow-release fertilizer at the rate on the label. Established shrubs in good soil often need little extra feeding, so let weak growth or pale foliage guide you.

Stop feeding by late summer so new growth can harden before winter.

The PlantoScan app can remind you when to water and when to fertilize each plant.

Choose a spot with full sun to partial shade and well-draining, loamy soil with good organic content. Avoid low spots where water collects after rain.

Twin Arnica is suited to USDA Zone 4a – 8b.

Plant container-grown or balled-and-burlapped shrubs in spring or early autumn, setting the root flare at soil level, and water well after planting.

Twin Arnica can spread to about 1 ft (0.3 m) and reach about 2 ft (0 m) tall. Space plants about 1 ft (0.3 m) apart so mature crowns don't crowd each other, and plant at least half that distance from buildings, fences and paths.

Planning a row or hedge? Try the plant spacing calculator.

Prune Twin Arnica while it is dormant in late winter: first remove dead, damaged and crossing branches, then thin lightly for shape.

If it flowers in spring, prune right after flowering instead so you don't remove next year's buds. Never take off more than about a quarter of the shrub in one year.

Twin Arnica is hardy down to USDA zone 4a, so once established it can stay outdoors through winter in that zone and warmer ones.

Water deeply in late autumn before the ground freezes, and spread a 5–8 cm (2–3 in) layer of mulch over the root zone, keeping it away from the trunk.

Young and container-grown shrubs need extra protection: roots in a pot freeze much more easily than roots in the ground.

Twin Arnica can be propagated through seeds, division of rhizomes. Similar propagation techniques also apply to doronicum acaule plant care, which shares the same genus.

See all plants toxic to cats and plants toxic to dogs.

Twin Arnica is susceptible to aphids, whiteflies, spider mites. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.

Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.

Twin Arnica grows outdoors in USDA Zone 4a – 8b. It survives winters down to planting zone 4a. Twin Arnica is native to Western Canada and the Western United States.