Louis on the Loose

Rough-leaved Hydrangea

Surprise!  This staggering beauty, normally thought to be hardy only in mild climates, thriving in the sterner hills of Connecticut, at one of the great East Coast nurseries, Broken Arrow.  See more in The Gardening Journal.

Here's how to grow this fuzzy-leaved beauty:

Latin Name

Hydrangea aspera 'Rocklon'

Common Name

Rough-leaved Hydrangea


Hydrangeaceae, the Hydrangea family.

What kind of plant is it?

Deciduous shrub.


Zones 6 (5 if you're lucky) to 9.  Much hardier than the 7 - 9 originally thought.


Broadly upright and full.

Rate of Growth

Fast when it's happy.

Size in ten years

Six feet tall and five feet wide.  Eventually ten feet tall or higher, eight to ten feet wide.


The conspicuously large, smooth-edged, and come-stroke-me felted leaves give this bulky shrub a people-person personality.  If a bassett hound had hundreds of ears—oddly, but in a pleasant Alice in Wonderland way—and had been—also oddly, but in a pleasant Alice in Wonderland way—turned into a flowering shrub, the hound would be this hydrangea.

Grown for

the foliage!  The leaves can be ten inches long, and are irresistibly fuzzy.

the stems!  The young ones of 'Rocklon' are fuzzy purple.

the flowers!  'Rocklon's start as massive branched pink clusters as big (and, seemingly, as heavy) as your first, that open into enormous one-foot mandalas of mauve-blue flowers surrounded by large white bracts.

Flowering season

Late Summer into Fall: August to hard frost in October.


Rough-leaved hydrangea has been fooling most of us for years, nurseryfolk and mad gardeners alike, as the epitome of mild-climate fussiness:  No chilly winters, no gusty winds, no strong sun.  And, in truth, it thrives in such pampered locales.  But it also thrives (on occasion) in stern central Massachusetts, which is Zone 6 only when you squint your eyes and mulch like hell.  See "Louis on the Loose" for a voluptuous and unstinting specimen extremely happy in the high hills, fully exposed, of Connecticut, where there's not a whiff of Zone 7 around.  This is the 'Macrophylla' cultivar, not 'Rocklon', true, which may be a bit hardier.

No matter where you garden, this is a plant for full sun if you can give it great soil that doesn't lack for moisture, especially in the hot months.  Afternoon shade is wiser if you're less confident.  I hear that the foliage is even larger when the bush gets some shade, which seems like all the encouragement needed to provide dappled sun instead of the straight stuff.

How to handle it

I keep my 'Rocklon' in a pot so it can winter, leafless and dormant, in my moist dirt-floor basement, and summer, leafy and in wind-free total shade, under the pergola in the Red Garden.  Beyond that cycle of schelp-in, schlep-back-out, I've been a neglectful Rocklon steward.  The bush repays me in kind, with foliage that's half the size it should be on a shrub that's barely growing.  This is my year to repot it extravagantly, water it conscientiously, give it more sun, and, in general, demonstrate that I care.  And next Spring is my chance to plant it in my Pink Borders.

For hydrangea-specific care, keep in mind that H. aspera needs the same pruning as a mop-head hydrangea.  It blooms only at the tips of the stems it's been growing this season, as long that those stems arose from older stems it grew last season.  Stems that grow directly from the base of the shrub won't bloom their first season.  Each Spring, wait until the shrub has started to leaf out, so it will be obvious which stem tips (or, indeed, entire stems) have been winter-killed.  Prune just those down to the first pair of green leaves, and then let the bush grow and flower on its own while you attend to its diverse needs for shelter, moisture, shade, and, in general, the life of Reilly. 

This large and riviting shrub demands close viewing, and the velvety leaves and stems are irresistible for stroking, too.  So despite its eventual size, plant it within reach of the front of the bed.  Otherwise you and all your friends will just tromp right through the bed to get to it.  Partner with fern-leaved or narrow-leaved groundcovers.  Ferns and liriope: done!  Or even astilbes if they get enough water through the hot late-Summer weeks, when the hydrangea is at its peak.  And to the side, or even at the back, pick up the dusty pink of the stems and buds (and, of course, the flowers that follow) with, say, a pollarded Acer negundo 'Flamingo', whose pink-flushed leaves and three-leaflet foliage will coordinate well.

As usual with a plant whose hardiness is still not confirmed broadly, planting on a slope, no matter how gentle or how small, maximizes whatever Winter hardiness your individual plant actually has.  If there's a fence or building or big spreading conifers to the north, even better.


There's still confusion about just how hardy this shrub is, so you're taking your chances in Zone 6 and you're intrepid, indeed, in Zone 5.  On the other hand, the more gardeners who try this shrub at the lower margins of its supposed hardiness, the sooner we'll all be certain of just how tough the plant is.


Hydrangeas are as much of a "whole world" as roses, orchids, grasses, hostas, daylilies, succulents, dwarf conifers, alpines, viburnums, or lilacs:  As with all of these specialties, there are a lot of species and uncountable hybrids and cultivars.  There's a modest range even of H. aspera, too, of hardiness and leaf size (bigger is better, fuzzier is better).  While most of us could be content with just one H. aspera, few gardens can be credible without a generous array across the range of hydrangea species.  I aready have (gulp) over two dozen hydrangeas—and I don't mean just different colors of mopheads, either—and look forward to more.




By cuttings.

Native habitat

The straight species is native to the Himalayas; 'Rocklon' itself is from England.

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