Siam Mahonia Plant Care

Siam Mahonia (Mahonia siamensis) belongs to the Berberidaceae family within the Mahonia genus. Siam Mahonia is native to China and the Himalayas.

Siam Mahonia displays an upright, spreading shrub growth habit, reaching up to 6 ft tall with a spread of approximately 4 ft. Siam Mahonia produces clusters of fragrant yellow flowers in late winter to early spring.

Leaf size: approximately 12 inches.

Water a young or newly planted Siam Mahonia every 7–14 days, soaking the whole root zone, until it is established — usually one to two growing seasons. Established trees mainly need water during long dry spells. In a container, water whenever the top few centimetres of soil are dry.

Siam Mahonia thrives in partial to full shade. The optimal light range is 100–500 lux. Avoid placing Siam Mahonia in direct, harsh sunlight for extended periods, as this can scorch the foliage.

Mahonia siamensis tolerates temperatures of 45–75°F. Siam Mahonia prefers humidity levels of 40–70%.

Moist, well-draining acidic soil with added organic matter. Good drainage is essential for Siam Mahonia to prevent waterlogging, which leads to root rot and fungal issues.

Feed Siam Mahonia every 8 months during the growing season with a balanced, slow-release fertilizer at the rate on the label. Established trees 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 partial to full shade and moist, well-draining acidic soil with added organic matter. Avoid low spots where water collects after rain.

Siam Mahonia is suited to USDA Zone 11b.

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

Siam Mahonia can spread to about 4 ft (1.2 m) and reach about 6 ft (2 m) tall. Space plants about 4 ft (1.2 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 tree spacing calculator.

Prune Siam Mahonia 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 tree in one year.

Siam Mahonia is frost-tender (hardy to USDA zone 11). In colder areas grow it in a container and move it to a bright, frost-free place before the first frost.

Siam Mahonia can be propagated through seeds, division of rhizomes.

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

Siam Mahonia is susceptible to aphids, scale insects, 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.

Siam Mahonia grows outdoors in USDA Zone 11b. It survives winters down to planting zone 11b. Siam Mahonia is native to China and the Himalayas. In cooler regions, grow Siam Mahonia as a houseplant or bring it indoors before the first frost.