How to Grow Castor Aralia — Kalopanax 

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Kalopanax–commonly called castor aralia or tree aralia–is a deciduous tree with a spreading, round habit. Kalopanax bears large palmately lobed leaves that can exceed one foot (30cm) in width. Kalopanax also bears large terminal, umbel-like tiny white flower panicles in late summer. Tiny black fruits follow the flowers and are quickly eaten by birds.

Kalopanax has a tropical look but is Hardy to USDA Zone 5. Kalopanax grows to 30 feet (10m) tall and wide. Kalopanax has a spiny trunk and spiny branches; it has relatively few branches. Spines eventually disappear from the trunk and larger branches.

Kalopanax is a genus of one species. It is native to forests in East Asia.

Leaves of a castor aralia, Kalopanax septemlobus
Leaves of a castor aralia, Kalopanax septemlobus

Get to know Kalopanax 

  • Plant type: Deciduous tree 
  • Growing zones and range: Zones 5 to 9
  • Hardiness: Hardy to Zone 5
  • Height and width: To 30 feet (10m) tall and wide 
  • Growth rate: Fast 
  • Form and habit: Spreading, attractive, rounded habit 
  • Foliage: Large, in variably shaped, palmately lobed leaves, which are arranged alternately and vary from hairless to very hairy beneath 
  • Flowers: Large, terminal, umbel-like panicles of usually white, 4- or 5-petaled flowers 
  • Fruits: Spherical, tiny, blue-black fruit 
  • Bloom time: Late summer 
  • Uses: Specimen tree 
  • Common name: Castor aralia, Tree aralia 
  • Botanical name: Kalopanax 
  • Family name: Apaliaceae 
  • Origin: East Asia 

Where to plant Kalopanax 

  • Plant Kalopanax in full sun or partial shade, preferably sheltered by other trees and shrubs. 
  • Plant Kalopanax in fertile, moist but well-drained soil. 

When to plant Kalopanax 

  • Sow Kalopanax seed in containers in a cold frame in autumn.  

Planting and spacing Kalopanax 

  • Plant Kalopanax 30 feet (10m) apart. 
  • Plant Kalopanax deep to accommodate the tree’s long root structure. 

How to water and feed Kalopanax 

  • Give Kalopanax regular water. 
  • Feed Kalopanax with an all-purpose organic fertilizer in spring. 
Spiky trunk of Kalopanax
The very spiky plant stem of the Kalopanax, also known as Castor Aralia.

How to care for Kalopanax 

  • Prune young Kalopanax trees at any time during the spring; old trees rarely require pruning.  

Kalopanax pests and diseases 

  • Pests and diseases are infrequent.  

Kalopanax propagation 

  • Take Kalopanax greenwood cuttings in early summer. 
  • Sow seeds in a container in a cold frame in autumn.

Kalopanax varieties to grow 

  • Kalopanax pictus, Castor aralia, spreading, deciduous tree with spines on the trunk and shoots, and variably shaped, shallowly to deeply 5- to 7-lobed, dark green leaves, to 14 inches (35cm) or more across, which vary from hairless to very hairy beneath. Large, umbel-like panicles, 8-12 inches (20-30cm) long, of small, 4- or 5-petaled white flowers, .06 inch (2mm) across, are borne in late summer, followed by spherical, blue-black fruit, .13 inch (3mm) across. To 30 feet (10m) tall and wide. China, Korea, Russia (South Kurile Islands, Sakhalin), Japan (Ryukyu Islands). 

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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