Castor Aralia



This is Maximowicz’s castor aralia, with the arm-length Latin name of Kalopanax septemlobus var. maximowiczii.  The "Terminator"-like buds of the young branches perch, reach to strike, atop impregnably-thorned stems.  Yes, sometimes "interesting" also means beautiful, and I'm into beauty.  Just wait until my wisterias are in bloom. 


But sometimes "interesting" means unsettling.  And sometimes, for certain folks, me included, unsettling can be beautiful in itself.


Castor aralia's buds and thorns are (to me) so interesting that I'll even forgo the tree's striking late-Summer flowers if it means more thorns, more buds.




All I need to do to inspire the plant to be at its thorny and well-budded best—a thorny and well-budded beast— is to inspire it to produce more young stems.  And that, of course, means pruning.  Aralias are always all too happy to respond by letting their many side buds spring into growth. 


(Geek Alert:  Buds at the end of branches produce a hormone that usually inhibits the growth of buds farther down those branches.  Makes sense: The growth at the tip is getting the most sun, and is out of the way of ground-level predators too.  The plant should put its energy into growing those favored branch-tips taller instead of producing side shoots in its shade that are also more vulnerable to predation from below.  Pruning removes these terminal buds, and therefore the growth-inhibiting hormone they produce.  So the buds further down the stem are now free to grow.  And they do: The branch branches.  It bushes out.)


See the little bud at the end of my finger?  It's almost at the bottom of the trunk, and yet is starting into growth even though the trunk above it isn't even pruned off.  And, if you look closer and longer, you'll see another bud or two even lower.




Imagine how joyfully they'll grow without the hormonal kibosh from the buds above.  This is a species just calling out for a tall guy who travels with loppers at the ready. 


In a minute, the deed is done.  The stump will branch out the moment the weather becomes even passably warm.




Notice another aralia characteristic:  Stems that sprout directly from the roots.  Like all of this tree's young stems, they are amazingly thorned.  Nice!




Here's another, on the back side of the trunk.




What with the root sprouts and the sprouts directly from the trunks, both of which are "freed" by lopping off the trunks above them, taking this caster aralia down to stumps each Spring will soon transform it into a thick colony of fierce stems. 


The annual massacre also seriously limits the plant's overall size, which is always a plus in my only-an-acre-and-a-half.  My guess is that a "Spring-lopped" kalopanax won't get over five feet tall or wide.  Ever.  A free-range kalopanax grows as big as—and, indeed is—a shade tree.


For the gardener that hopes to try just about everything—and to grow as many of them as possible—smaller is always better.  For this gardener, fierce is fabulous at any size.




Here's how to grow this proudly-protected tree:


Latin Name

Kalopanax septemlobus var. maximowiczii

Common Name

Castor aralia.  ("Castor" from the leaves' tropical size and resemblance to the castor-oil bean, the unrelated Ricinus communis.  "Aralia" from the club-like and (when young) aggressively thorny trunks and branches, plus the large and complex Summer flower clusters.)


Araliaceae, the aralia family

What kind of plant is it?

Hardy deciduous tree


Zones 4 - 8


Upright, usually single-trunked.  Large palmate leaves look tropical in a temperate-garden context.  Young stems are impressively as well as colorfully thorny.

Rate of Growth

Fast when young; moderate when older.

Size in ten years

Fifteen to twenty feet tall, ten to fifteen feet wide.  Eventually to thirty or forty feet tall and twenty-to-thirty wide, i.e., of shade-tree size.


Depending on your priorities, the large foliage can look either lush or coarse.  Branching itself is sparse and heavy.

Grown for

Unusually large and "tropical" foliage.  Unusually late Summer flowering of very large (to two feet across!) and complex clusters of round heads of small white flowers.  Which bees adore.  Developing at the very tips of the new growth, the flowers are fully exposed, and are backed beautifully by the large leaves.  Young (as well as coppiced) plants are extremely thorny, which, again depending on your priorities, can be exciting or horrifying.  The overwintering buds for next Spring's foliage at the tips of young branches are impressively determined-looking.

Flowering season

High Summer: July and even August, when almost no other hardy trees are in bloom.


Full sun, any soil that's well-drained. 

How to handle it

As a shade tree, just plant it and stay out of its way.  The lower branches, and the trunk itself, gradually grow out of their juvenile thorns.  Or, coppice in early Spring to keep as a large shrub that celebrates the fierce thorns but doesn't bloom.




Maximowiczii has the most dramatically "fingered" leaves, with (usually) seven distinct lobes.  The species (as well as individuals) can be less fingered.


Thorniness of young plants usually dissuades all but the cognoscenti from buying this.  Too bad!  Head for "destination" specialty nurseries, or shop on-line.


Grafting and seeds, and as well as an early-Spring chop-out of the occasional root sprouts from the mother plant.

Native habitat













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