A Gardening Journal

Today in the Garden of a Lifetime: Big-Root Geranium

No temperate garden should be without big-root geraniums. Of all the hardy geraniums with reputed groundcovering prowess, big-root is the most successful where summers can get into the nineties. No wonder: It's deer-proof, fairly shade-tolerant, weed-smothering, shrub-nuzzling, outward-flowing, immortal when happy, and madly floriferous as spring ripens into summer.

 

Geranium macrorrhizum Album 060617 overall 640

 

This is the white-flowered variety of my modest collection: Geranium macrorrhizum 'Album'. The species name—macrorrhizum—literally means big root. Long rhizome would be more accurate: the perennial expands outward via ropy rhizomes that spread over the surface of the soil and only occasionally, as if by reluctance or afterthought, extend actual roots into the soil.

 

Dividing big-root geranium, then, isn't a matter of anything anyone would dignify as actual digging. Instead, you grasp the edge of the mat of foliage and lift it upward, as if you were going to sweep crumbs under the carpet. Cut outer hunks of the rhizomatous tangle free with pruners, pull them apart into more-or-less single hunklets of foliage-bearing rhizomes, and replant by shallowingly covering each rhizome with soil. Spaced two feet apart in good soil, divisions will provide nearly full coverage during the following year.

 

Once you've gotten the feel of big-root geranium mats, you can harvest them "blind," by which I mean chopping perimeter hunks free with a spade without bothering to kneel down and lift up the matted growth first. (A shovel has a rounded bottom edge that comes to a point; a spade has a straight bottom that, as here, can be very effective at dividing clumps of perennials.) While it's easiest to do this in early spring before new foliage has emerged, big-roots will tolerate division at almost any time—even high summer—as long as you provide some shade and water as the hunklets re-establish.

 

This clump of Geranium macrorrhizum 'Album' is four feet across and nearly ten years old. It receives no care at all, and is so vigorous that you'd never know that six weeks ago about a third of it was uprooted and divided up for a local plant sale. New growth had come flooding back, perhaps because the mother clump was, in effect, thinned out for the first time in a decade.

 

Because Geranium macrorrhizum is a snap to divide, why haven't I spread this workhorse garden-wide? Time for a closer look. This perennial's fuzzy green leaves go with anything, but no matter which of the many cultivars you choose, they all celebrate pink. Sure, when the petals themselves are pink or magenta, it's clear that big-root geranium won't be your groundcover of choice for areas of your garden saturated with yellow, orange, or red. 

 

But this is the white-flowered form, the Album of all the cultivars. Regardless, the effect of the blossoms is only moderately of true white because, in detail after detail, they are anything but pink-free.

 

Geranium macrorrhizum Album 060617 fingers closer 640

 

Look at the close-up below: Veins of pink extend outward from the base of the petals. The white stamens turn pink just before they terminate in the tan bean-like anthers. And at the top of the picture, see what has happened after those petals are shed? The pale pink tips of the stamens have intensified to Hawaiian Punch, while the flowers' raspberry-pink calyces have become fully revealed.

 

Geranium macrorrhizum Album 060617 fingers closer still 640

 

Regardless that its petals themselves are—for a big-root—comparatively white, there is so much pink in the overall floral performance that Geranium macrorrhizum 'Album' looks best when its playmates avoid yellow, orange, and red. Instead, this "white" big-root can calmly accompany only neutrals such as green and burgundy; the only hues it can truly embrace are overtly pink-centric ones such as raspberry, rose, purple, and, well, pink. 

 

My gardens have substantial pink-friendly areas—a pair of pink borders each sixty feet long—plus some all-green stretches where pink couldn't clash: My Album is planted on the shady north side of my hedge of American beech, with no other colorful ornamentals within twenty feet.

 

But, still, pink is one of the most limiting colors to highlight in any temperate-climate garden, because so few plants with any pink in them at all have it anywhere other than in their flowers. And hardy plants tend to be in flower just for days or weeks, not months.

 

Quick: name even one pink-leaved plant besides pink-leaved coleus or caladiums. Both of them are tropicals that can only function in temperate climates as warm-weather annuals. Here are five of the very few pink-foliaged plants, all in my pink borders, that are hardy in Zone 6 or colder: pink-leaved chestnut, Flamingo boxelder, variegated Japanese clethra, pink-leaved Chinese mahogany, feather-leaved Japanese oak, and dappled willow. Plus, there's a Japanese maple cultivar that flirts with pink; it, too, is named Flamingo. There's a variegated red maple, Snowfire, whose new leaves are pink; I'll profile this tree this summer. And there's the tricolored European beech, whose purple leaves have a slender edge of pink that's visible at close range.

 

All of these hardy pink-foliaged plants are thrilling, but in mostly subtle ways. Plus, they are all deciduous, so bring no pink to the garden from fall into spring. Worse, not a one of them has the brash season-long pink energy that, say, gold-leaved Scots elm gets from its yellow foliage, or purple smokebush gets from its burgundy. Worse still, there are scarcely any other options for hardy pink-foliaged plants. There are many other choices for hardy plants, both deciduous as well as evergreen, whose leaves are vividly and durably yellow (or burgundy). How about this gold-leaved conifer? Or this one? This gold-leaved holly? Or this one?

 

In my book, then, pink is rightfully and strategically relegated to sideshow status. It's a bit player on the vast stage of any comprehensive garden that can't possibly succeed without the all-hands-on-deck participation of colorful foliage at every turn. And the great majority of those "hands" flaunt yellow or burgundy, not pink. So even an otherwise perfect perennial such as white big-root geranium has only a walk-on role.

 

 

Here's how to grow another easy hardy geranium, Anne Thompson. She is hardy "just" to Zone 4, whereas big-roots are hardy down to Zone 3 (which is Ottawa, folks). Anne's plum-petaled flowers and chartreuse foliage gain her entry into the garden's widespread areas that are, by choice as well as necessity, yellow-friendly. But her lacy, far-ranging growth doesn't have the groundcovering ability of a big-root.

 

 
 
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