Virginia Mountain Mint

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The button-like flowerheads of Virginia mountain mint dry to an unusual pewter hue, and will last through the Winter if ice or snow don't crush them. In Winter, Pycnanthemum virgnianum is spare, sophisticated, and eccentric. What a difference from this easy perennial's warm-weather gestalt, which is dense, delicate, and cottagey.

 

The flowerheads' chilly blue-gray would be a winning partner to the chilly green-gray of shield lichen, which, with luck, will volunteer on one of the trunks of nearby ornamental trees for which my colony of this mountain mint is groundcovering.

 

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Here's how to grow this easy perennial:

 

Latin name

Pycnanthemum virginianum

Common name

Virginia Mountain Mint

Family

Lamiaceae, the Mint family.

What kind of plant is it

Herbaceous perennial.

Hardiness

Zones 4 to 9.

Habit

Slender unbranched stems grow in dense and quickly-spreading colonies. 

Rate of growth

Fast.

Size in ten years

Three to four feet tall and, unless restrained, ten feet or more across. 

Texture

Delicate in both leaf and flower.

Grown for

its Summer flowers: Small but profuse heads of tiny white flowers that are dotted with lavender. They dry in place for a second season of interest in Winter.

 

being critter-proof. Mountain mints release their namesake fragrance when brushed. Browsers leave them alone.

 

its vigor: Pycnanthemum virginianum grows densely enough to function as groundcover.

 

its durability: Pycnanthemum virginianum is hardy as well as tolerant. Unless you work at removing it, you'll have a colony for life.

Flowering season

High Summer: July into August. The flowerheads dry in place, and are subtly effective through Winter. 

Color combinations

The green leaves go with everything, but the lavender-dotted flowers suggest partners that are pushing pastels. The flowers are so small that, as long as neighboring colors are muted, it doesn't matter what their colors actually are.

Partner plants

Because the coloring of Pycnanthemum virginianum is modest even when the colony is in full flower, pair with other plants on the basis of its habits more than its aesthetics.

 

As is typical for mountain mints, growth is dense enough to work as groundcover—and, given the plant's height, a fairly tall one. Because the plant's profuse rhizomes spread quickly, your groundcover will, indeed, cover a lot of ground. You might be able to keep the colony from swamping nearby plants that are smaller—see "How to handle: Another option—or two!"—but whenever possible, limit neighboring plants to those that are much taller and whose growth arises from only a trunk or two. Then the mountain mint's roots and stems can both flow harmlessly around them.

 

Avoid near neighbors whose growth is multi-stemmed, even if that growth is strongly upright and comfortably taller than that of the mountain mint. Pycnanthemum will infiltrate those plants' bases; this doesn't harm the "infiltree," but it does look messy. It's best, then, to avoid pairing with any shrubby ornamentals such as lilacs, roses, spirea, summersweet, viburnum, and weigela. Further, even when they are tall enough, the multi-stemmed habits of most ornamental grasses and perennials are likely to be problematic for the same reason. Only "multi-stemmers" of unrivaled groundcovering prowess might be able to keep Pycnanthemum at bay: It would be a worthy experiment to pair mountain mint with butterbur or, on the shady side, massive hostas.

 

Shrubs and perennials with a mounding habit are especially awkward. If the growth of Pycnanthemum doesn't grow under the low canopy and then send stems up through it, it can still grow near enough to shade the canopy out. Even when that isn't a worry, it's not a great look: The mounding shrub will always appear to be at risk of being overwhelmed.

 

In my own garden, one pairing has been unexpected but trouble-free: Danewort, Sambucus ebulis, an unusual herbaceous relative of elderberry that also grows from vigorous and far-reaching rhizomes. Its habit is tall (easily a foot taller than that of Pycnanthemum) and rangy. Compared to the cast-of-thousands march of Pycnanthemum, there are comparatively few stems in a stand of Sambucus ebulis. With only a bit of thinning, it's easy to dial back the colony's presence such that only occasional stems pop up through the outer limits of the Pycnanthemum colony.

 

Pycnanthemum has broader use as filler at the front of ornamentals whose growth arises from a trunk, or a very few main branches. In my garden, a pollard of Acer negundo 'Violaceum' is at the back of the colony, an archway of Cornus kousa 'Wolf Eyes' to one side, and a bluestone walk at the front. Only the other side provides sunny encouragement for expansion into nearby perennials—but that's the side that's given over to Sambucus ebulis. Other ornamentals with upright habit and few trunks include Clethra barbinervis and almost any tree, such as Alnus glutinosa 'Imperialis' or Salix babylonica 'Crispa', that you've decided to grow as a pollard.

 

The big opportunity for planting Pycnanthemum where it can explore at will would be in a more casual or even naturalized context, where dense growth of all the participating ornamentals can intermingle however they're able. All the better for them, too, in that their growth—which is, literally, "interleaving"—can synergize into a fearless groundcover.

Where to use it in your garden

Easiest as an informal but effective filler on the sunny side of larger shrubs and even trees, provided that they don't cast enough shade to thin out the growth of Virginia mountain mint to a less-than-effective density.

Culture

Part to full sun, in almost any reasonable soil. Revels (but also runs) in rich soil with bountiful water. Easy!

How to handle it: The Basics

This tough and tolerant perennial can be planted in Spring or Fall. If planted amid much larger neighbors, the colony can be allowed to spread ad libitum, to form an effective and large-scale groundcover.

 

Because self-seeding is not (at least in my experience) a problem, stems can be left in place through the Winter. Before new stems emerge in the Spring, cut last season's to the ground at your convenience.

How to handle it: Another option—or two?

The innumerable outward-bound stolons of Pycnanthemum virginianum are shallow and easy to dig out as long as they haven't infiltrated into any neighbors whose growth is multistemmed, from which its wandering growth would be maddening to extract. See "Partner plants," above for practical as well as pleasing suggestions for near neighbors. 

 

If possible, site where the colony can be restrained without further effort. Plant alongside paving or walls, or back the colony up to fresh water. If some or all portions of the colony need to have access into as-yet-uncolonized areas of a bed, edge the colony at any time in the season.

Any (other) quirks or special cases?

None.

Downsides

In favorable circumstances—decent soil, full sun or nearly so, and plenty of water—Pycnanthemum virginianum can spread outward with daunting vigor. See "How to handle it" and "Where to use it in your garden" for practical tips. On the other hand, this species doesn't self-seed, at least

in my experience, despite being both native and patronized by all possible pollinators.

Variants

There are about twenty species of Pycnanthemum, all native to North America. The genus is notable in producing almost no new forms; to my knowledge, there is only one named cultivar (see below) in the entire genus. Even so, there's enough variety that any garden could welcome several forms of mountain mint without worrying about repetition. Certainly, no garden should be without at least one of them, because the flowers are mobbed, even besieged, by every pollinator in the neighborhood, including bees, butterflies, wasps, and who-knows-what else. A colony in full bloom will be visited by many hundreds of eager insects, all in a seeming frenzy of feeding. It is a joyful and noisy highlight of Summer.  

 

The first species to welcome into your garden, and into the lives of so many communities of insects in your neighborhood, is Pycnanthemum muticum. Each of its small buttons of tiny white flowers is flanked by a pair of silvery-white bracts that, en masse, exponentially expand this species' visual presence. A large colony shimmers even at a great distance. You'll hear the jubilant mega-buzz of the colony's uncountable hoard of pollinators long before you're close enough to appreciate any in detail.

 

The foliage of Pycnanthemum tenuifolium is so narrow that, before it flowers with typical small heads of tiny blossoms, the clump is readily mistaken for an unusually-large form of the thread-leaf of coreopsis, C. verticillata. The flowers of P. tenuifolium 'Cat Springs' are larger than usual (although no Pycnanthemum blossom could be called sizable), and are pure white.

 

Each of the tiny flowers of Pycnanthemum flexuosum is lavender, and emerges from a white calyx with long projecting thread-like lobes that give this species' flowers a texture and prominence unique to mountain mints. This species is also notably less "spready" than is typical.

 

Visually, Pycnanthemum pilosum is not notably different from P. virginianum; its flowering season is reported to be even longer, from July through August.

 

Availability

On-line.

Propagation

By division. You could germinate the seeds of this species, but the plants are so vigorous, stoloniferous, easy to divide, and (seemingly) loathe to form new forms that it's much simpler to propagate vegetatively.

Native habitat

Pycnanthemum virginianum is native to eastern North America.  

 
 
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