A Gardening Journal

The Best Season Ever: Salt Marsh Mallow

Kosteletzskya virginica flower 081115 640

 

Delicate pastel flowers for months—nearly all Summer for me—are reason enough to grow this native mallow. Plus, it's tall and tough, and will grow in brackish water as well as normal garden soil. Yes, the flowers are petite, just two inches across. But a thriving clump will produce hundreds of them over the season.

 

Thanks to prolific side stems, even after the flowers at the tip of the stem have matured to countless seed heads, the floral display continues. Kosteletzkya virginica begins flowering in June—and can still be blooming in September.

 

Kosteletzskya virginica seeds heads 081115 640

 

Small flowers don't mean small plants, though. For me, Kosteletzkya soars over eight feet on thick and sturdy stems that display pointed green leaves the size of many a maple's. In the mid-July picture below, stems of one of my spectacularly misplaced colonies have elbowed their way up through a ginkgo standard into the soon-to-flower stems of trumpet vine. The contrast of the pale pink of the Kosteletzkya and the bright orange of the Campsis will be scary, indeed. 

 

Kosteletzkya virginica overall 071915 640

 

Fortunately, Kosteletzkya is easygoing about being transplanted. Come this Fall, this colony will be welcomed into the congenial colors of the pink borders.

 

Here's how to grow this unique native perennial:

 

Latin Name

Kosteletzkya virginica, also known as Pavonia virginica.

Common Name

Salt marsh mallow, seashore mallow, Virginia mallow

Family

Malvaceae, the hibiscus family.

What kind of plant is it?

Hardy upright herbaceous perennial that many gardeners will mistake for some form of Lavatera, a related genus of mallows native to Europe, Asia, and western North America. Besides L. cachemiriana and (say only some sources) L. thuringiaca, most of those are either tender below Zone 7 or annuals, not a persistent perennial like Kosteletzkya. In eastern North America, choose Kosteletzkya instead. 

Hardiness

Zones 5a - 10b.

Habit

Strongly vertical. Each clump has a few very tall thick stems with many comparatively short side branches on the upper two-thirds. Unlike hollyhocks, which Kosteletzkya somewhat resembles both in habit and in flower, there are very few basal leaves; instead, they are evenly arrayed throughout the upper portions of the stems.

 

In my experience, the stems are admirably self-supporting when they receive fairly even sun all around. The tips of stems that receive light principally from one side don't bend toward the sun but, rather, the entire stem can lean more and more from the base. See the second "How to handle it" box for suggestions on staking.

Rate of Growth

Fast.

Size in ten years

Clumps are much wider when measured two thirds of the way up than at the base. One that's a foot or two wide at ground level can be four to six feet wide higher up. Although my colonies grow terrestrially—i.e., not in the shallow water that this perennial can also thrive in—and don't receive supplemental irrigation, they are still much taller than generally listed: eight to nine feet instead of three to five. Further, my growing season here in New England is weeks shorter than those of sources farther south, too, where typical heights for a given perennial tend to be the maximum. I'm not growing an 'Altissima' cultivar, either—there isn't one. It's likely that clumps growing with full exposure to wind will be shorter than those, such as in my garden, that enjoy substantial shelter. 

Texture

Bushy. Thanks to its height and the large foliage, which is the size and shape of that of the shade-tree maple, Acer pseudoplatanus, and arrayed evenly up the tall and many-branched stems, Kosteletzkya can be dense enough to function as a warm-weather screen. 

Grown for

its tolerance and adaptability: Provided it receives at least a few hours of full sun, and its soil is at least occasionally moist, Kosteletzkya can thrive in a striking range of sites and conditions: from soil that is literally swampy (and even swampy due to brackish water) to that which is heavy and clayey, to that which drains quickly but provides ready water at deeper depths (as in, say, sandy soil at the beach). It will also thrive in sites that are fully exposed to wind as well as those that are still; in climates whose Winter temperatures are stern indeed (down to minus twenty degrees Fahrenheit) to subtropical ones where frosts are mild as well as rare.

 

its easy height: Stems of Kosteletzkya are strong without being brittle, and are usually self-supporting. If staking is needed, it is easy to implement. See the second "How to handle it" box, below.  

 

its long season of bloom: Unusual for a typical perennial, Kosteletzkya is typically in bloom for two or even three months, not weeks. 

Flowering season

Summer: July into September.

Color combinations

The clear pink of the flowers limits the straight species of Kosteletzkya to contexts that celebrate pastels of almost any shade, as well as the pink-friendly colors (in any degree of saturation) of white, rose, blue, violet, and burgundy. Steer clear of red, orange, and deep yellow. Because flowers with hot colors are easy to achieve in the warm months when the pastel-pink flowers of Kosteletzkya are out, take care to site both color "camps" with plenty of separation by neutral green.

Plant partner

Whether growing in damp ground, aquatically, or in normal garden soil, Kosteletzkya is easy to combine with plants that provide contrasts in texture and form, while still being clearly pink-friendly in coloring when the mallow is in flower through the Summer.

 

In ground with reasonable drainage year-round, all forms of Eupatorium provide large heads of tiny flowers, usually in shades of pink. Flowers of PG hydrangeas are a bit larger and, whether in their initial cream coloring or the shades of pink that creep in, harmonize beautifully. Flowers of pink dahlias, cannas, Crinum, or perennial hibiscus can be much larger (and in all shades of pink), and can emphasize the comparatively small blooms of Kosteletzkya.

 

In wetter or even aquatic sites, there are pink-friendly water cannas and crinums; most eupatoriums and perennial hibiscuses will be happier than ever, too. If you can establish a colony of lotus nearby—and keep it from smothering Kosteletzkya—its mammoth flowers would be the ultimate contrast. Most forms of lotus have pink-friendly flowers. The tall stems of Kosteletzkya would place its small blooms at the same height as those of the lotus, too.  

 

As is true with almost any color, burgundy is a strong yet congenial contrast. You can achieve it in normal soil with forms of Japanese maple, ninebark, and smoke bush, or those few forms of canna that combine dark leaves with pink flowers, such as 'Raspberry Truffle' and 'Skyhawk'. In wet ground, look toward forms of taro, such as Colocasia esculenta 'Red Stem Rhubarb'  or 'Dragon Heart'. 

 

Because its flowering season is longer than most hardy plants, and even many annuals and tropicals, it can be most successful to pair Kosteletzkya with plants that bring color through foliage, not flowers. All of the plants that supply burgundy, above, do so via foliage, so will be able to synergize with the pink mallow flowers no matter when in the season they appear. Here's one exception to consider: Hibiscus moscheutos 'Heart Throb', whose immense flowers are described as true maroon. I'm establishing a colony in my red garden—the flowers will go just as well with orange and red as pink—and hope to be able to post pictures of the flowers in 2016. Its peak of bloom will be in August, along with that of Kosteletzkya.

 

The large green maple-shaped Kosteletzkya foliage is also worth highlighting. It is just as good a contrast with burgundy-foliaged plants as with those whose leaves are variegated with cream or white. In normal ground, consider almost any of the variegated forms of miscanthus, and in wet ground, striped giant reed

 

Your need might not be contrast of texture or color at all, but of size: This tall clumping perennial will always benefit from something knee-high and mounding in front. As long as the flowers (if any) don't contrast, and the foliage isn't also maple-like, all options are open. If the location is on the shadier side of mallow, almost any hosta whose leaves are not celebrating yellow will work. On the sunny side, consider amsonia, whose feathery foliage would highlight the comparatively large Kosteletzkya leaves.

Where to use it in your garden

Its comparative lack of basal leaves makes Kosteletzkya perfect for siting amid medium or even tall herbaceous neighbors: There's no need to worry that the colony's lower reaches will be cast into shade by surrounding growth. That said, direct sun right at the base early in the season will encourage sprouting and quicker growth, so don't surround clumps with shrubs or evergreens that would block most low-elevation sun in the Spring. See "Plant partners," above.

 

Although it has skimpy basal foliage, Kosteletzkya doesn't demand to be sited in back of a lot of "fronters" on account of its bare ankles and shins. Its thick stems are green right to the ground, and the species' rarity in gardens, unusual height, and long season of bloom all make it worthy of a more center-stage spot. That said, these very qualities also make it an easy success even far back in the deepest, fullest borders. Another option would be to line a walkway with clumps planted three or four feet back from its edge, to form a striking Summer hedge.

 

Because Kosteletzkya shares with its perennial Hibiscus cousins the ability to grow in shallow water as well as in normally dry soil, it can thrive in rain gardens and drainage swales—let alone in ground permanently saturated with water (either sweet or brackish), as implied by its various "marsh" and "seashore" common names. Next season, I'll be digging up one of my clumps, dividing it, and trialing it in some of my different water-garden habitats. By keeping a clump in a large pot, I could place it just for the season in one of my water-filled horse troughs. I could sink another pot entirely in my reflecting pool to test and, I hope, confirm the species' ability to thrive, as is reported, when the base of the clump and its roots are all permanently submerged in shallow water.

Culture

Full sun and almost any soil that is reasonably moisture-retentive or has access to moisture at deeper levels. Because Kosteletzkya will thrive in standing water, there's no need to worry about providing good drainage. Even heavy clay soils, then, should be welcome. This is no surprise given that such heavy, low-oxygen, poorly-draining soils are often encountered throughout the heart of this species' native range: Virginia to Texas.

How to handle it: The Basics

Kosteletzkya needs little attention after establishment other than cutting down old canes any time that is convenient from Fall to early Spring. In my experience, colonies don't need periodic division to maintain their vigor; nor do they need dead-heading to prevent volunteers.

How to handle it: Another option—or two!

In case your clump doesn't receive even sun all around, it's likely that some stems will lean toward the light. There are several ways to help right them. Most proactively, place a peony hoop over the clump in early Spring. Because the stems could grow six feet and more above a hoop with legs just tall enough to handle peonies, consider pounding three five-foot segments of rebar into the ground—leave them in year after year—so that you can either tie the peony hoop's legs to them; or, even simpler, guide them up through the hoop's grid and tie them directly to the hoop's rim. You'll have a peony hoop that's between three and four feet above ground, not eighteen inches.

 

Guide three or four young stems through the hoop as they grow; with their prolific side branches, they alone can form a respectably full display. If you enjoy the show too much to sacrifice outer stems, you can lasso each loosely to the outside of the hoop's rim individually. They are sturdy and their upper portions are unlikely to snap; their side branches will soon hide their connection to the high-altitude peony hoop, let alone the hoop itself.

Another option—again, by using permanent heavy stakes that have been pounded in deeply—is, simply, to tie twine from stake to stake each season, for an informal corral for the central stems. Lasso individual outlier stems to the corral or the stakes.

 

Stems can be staked individually, too. Whichever option you choose, keep in mind the clump's shallow, thick, far-reaching roots. It will be difficult to detect them when putting in stakes, so all the better to place two or three permanent stakes when the colony is young.

Quirks and special cases

Kosteletzkya is likely to resprout from root fragments left behind during transplanting or dividing. If your goal is to remove a colony entirely, not just expand it, take care to follow the thick roots out as far as possible when you loosen the soil around the center of the clump. Possibly because this plant thrives in soil that is wet or heavy or both, roots don't penetrate deeply; there's no need when all the water you could want is right at the surface. So it's relatively easy to dig up everything. In this regard, Kosteletzkya is a welcome contrast to, say, horseradish, whose thick roots penetrate deeply and, seemingly, resprout from the smallest tips left behind, so that it is difficult to eradicate a colony without resorting to Round Up.

Downsides

Until its white cultivars became available—see "Variants," below—the pink flowers of the straight species of Kosteletzkya limited its range of companion plants (at least to those with sensitive eyes) to other plants that are also pink-friendly in the Summer. Many hardy plants that flower in Summer (in particular, many daisies with the exception of Echinacea) have flowers in clashing shades of deep yellow. 

Variants

The flowers of 'Immaculate' are pure white; this cultivar is reported as starting into bloom much later than the species—September, even—and continuing into October. Its size, handling, and hardiness are similar. Probably the same as K. virginica f. alba.

Availability

On-line.

Propagation

By seed: Despite its "nativity" to eastern North America, and the prolific seed set, I've never noticed self-seeding in my Rhode Island garden.

 

By division: In my experience, the thick and wide-ranging roots don't lend themselves to tidy handling. Almost inevitably upon digging, the clump separates into bare-root sections. No problem! They re-establish readily, and make it all the easier to create a swath of Kosteletzkya instead of a discrete colony. Plant shallowly—an inch or so of soil is plenty. As growth resumes, new roots will find their own ideal depths. Because Kosteletzkya is so hardy, division can be done in Fall as well as Spring in Zone 6 and warmer. In Zone 5, it is probably best to dig only in Spring.   

Native habitat

Kosteletzkya virginica is native from coastal New York down the eastern seabord into Florida, then along the Gulf Coast to Louisiana and Texas. 'Immaculate' was discovered in Louisiana.

 
 
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