Natural Selections

By Janet Allen

John Allen marveling at the luxurious growth of a large patch of knotweed along a road near our home in Syracuse, NY. Each time we pass this knotweed stand, we remark on its continuing growth and, so far, unchallenged spread along more and more of the roadside.

John Allen marveling at the luxurious growth of a large patch of knotweed along a road near our home in Syracuse, NY. Each time we pass this knotweed stand, we remark on its continuing growth and, so far, unchallenged spread along more and more of the roadside.

My husband, John, has an enemy – a persistent, aggressive one, taller than he is – up to 10 feet or more. After battling this foe on our church grounds for an entire summer, he believes he may be conquering it, albeit slowly. That enemy is Japanese knotweed (Polygonum cuspidatum, or Reynoutria japonica) also known as fleece flower, crimson beauty, Mexican bamboo, or reynoutria. Those who know it most intimately call it “killer bamboo.”

Japanese knotweed was introduced from East Asia to the United Kingdom as an ornamental plant in the early 1800s, and from there to the United States in the late 1800s. Despite its “bamboo” characterization, it’s actually a member of the buckwheat family. This upright, shrub-like perennial has smooth stems, swollen at joints where the leaf meets the stem. Its large leaves are somewhat heart-shaped. Its sprays of tiny greenish-white flowers in summer are followed by small winged fruit containing lots of tiny seeds.

Japanese knotweed has invaded disturbed areas of the eastern U.S., some Midwest and western states, and even Alaska. It tolerates a wide variety of conditions, including full shade, high temperatures, and high salinity. Although it tolerates drought, it’s often found near water sources.

It spreads primarily by rhizomes, but it can also spread by water- or wind-borne seeds. It can even sprout from discarded cuttings. It spreads quickly and crowds out native vegetation, even more aggressively than most invasives. It’s extremely persistent. And it’s tough, having been known to push up through pavement or disrupt house foundations. It greatly alters native ecosystems.

Knowing what a nasty plant this is, imagine our horror when we saw it featured in a garden tour a few years ago! A professional landscaper had actually installed this monster – and some garden center had actually sold it! Any of the native alternatives listed in the sidebar would have been at least as beautiful in that landscape.

The USDA’s National Invasive Species Information Center offers an online video at invasivespeciesinfo.gov/plants/knotweed.shtml. (Oddly, the video features Gabriel Fauré’s lovely Pavane as background music; Paul Dukas’ Sorcerer’s Apprentice would have been more appropriate.)

Eradicating knotweed

There are many ways to attempt to eradicate knotweed. A brief overview of some methods is described below, but if you’re preparing for battle this year, it would be wise to further explore the details as you plan your attack. You probably will need to use more than one of these methods and definitely over a long period of time. As one commentator put it, “Prepare to make its eradication your new hobby.” And remember, cuttings can regenerate, potentially spreading the problem beyond your yard, so regardless of the methods you use, thoroughly dry or burn any stalks or rhizomes prior to disposal.

Smothering is one approach. Cut down all the old canes, and cover the patch with a large, sturdy tarp or overlapping tarps. This method has the virtue of being organic and also offering the possibility of gardening in raised beds right on top of the tarps. You might as well garden on top of them. Research suggests that rather than dying, knotweed has the capability of going dormant for up to 20 years or possibly longer.

Another method is to apply glyphosate as a foliar spray in late summer or early fall – or even repeatedly throughout the growing season to slow it down.


 Want to do good AND eat well? Check out this recipe sent in by the great Kimie Romeo for Apple and Knotweed pie. Not even kidding.


A third method is to dig out the rhizomes, attempting to get every bit, since it can resprout from even the smallest piece left in the ground. Of course, it’s not likely you’ll get every bit since the rhizomes of an established stand can spread 12-15 feet and 6-9 feet deep. Some advise against this method since—besides being a lot of work—it spreads the rhizome fragments and disturbs the soil, making it easier for new knotweed to get established.

A local nature center appears to have had some success with another method. They immediately cut down any emerging sprouts throughout the entire growing season, with the goal of starving it to death.

Inspired, my husband faithfully traveled to church with his scythe each week last summer. He scouted for each new sprout popping up and chopped off its little head. As doubts crept in toward the end of summer, he escalated the battle, carefully applying glyphosate on the cut stems.

He has engaged his enemy on the church ground battlefield again this year, (somewhat) confident of eventual victory. And he has changed his method. Instead of cutting down emerging shoots, he’s pulling them out. He claims the knotweed is much less vigorous this year than last and predicts that after this year, he’ll need only to monitor the area occasionally. In fact, he’s already making plans to use this reclaimed area for native plants.

Who will win – my husband or the killer bamboo? Wifely loyalty demands that I bet on my husband, but more objective onlookers may have doubts. Poor guy. I’d better have a nice cup of tea waiting at home for him.

Native alternatives:

New England Aster (Aster novae-angliae)

Blue False Indigo (Baptisia australis)

Sweet pepperbush (Clethra alnifolia)

Silky dogwood (Cornus amomum)

Sweet Joe-Pye-Weed (Eupatorium purpureum)

Queen-of-the-Prairie (Filipendula rubra)

Virginia sweetspire (Itea virginica)

Maleberry (Lyonia ligustrina)

Fragrant sumac (Rhus aromatica)

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Spider flower (Cleome hassleriana) is a common, welcome volunteer. Photo by Larry Decker

Spider flower (Cleome hassleriana) is a common, welcome volunteer. Photo by Larry Decker

By Michelle Sutton   My friend Bill likes to say that, for both people and plants, “Volunteers are happiest.” Every year dozens of volunteer vegetable and flower seedlings emerge in my community garden plot, popping up conveniently in corners and inconveniently in the middle of paths.   Either way, I’d always assumed that as volunteers likely reverting to characteristics of one parent over the other (“reverting to type”), their flavor or beauty would be inferior, and I’d rogue them out. But I’m rethinking that now. Last year, volunteer snapdragons were quite showy, and I had some very tasty butternut squash from a volunteer plant.

Queen Anne's lace in the Coyne/DiNezza garden is embraced as one of the garden's signatures. Photo by Craig Coyne

Queen Anne’s lace in the Coyne/DiNezza garden is embraced as one of the garden’s signatures. Photo by Craig Coyne

With regard to plants of all types, how do we decide the fate of our volunteers? I asked for observations from popular garden writer, consultant, and speaker Sally Jean Cunningham (www.sallycunningham.org); from the co-creator of a multi-acre plant-lover’s paradise in Scottsville, Jim Lesch; and from Rochester Civic Garden Center trustee and owner of Perennial Designs (garden design & consulting), Milli Piccione.

Sally Jean Cunningham: As I have matured as a gardener, I am sadder but wiser about volunteers. I do remember being the young vegetable gardener who cheerfully welcomed a bit of “free” mint (Mentha sp.), imagining mint juleps and believing I had room for a few plants. Truth is: there is no such thing as a little mint.   That’s also true of most volunteer plants. The volunteer maple tree sapling is probably a Norway maple (Acer platanoides, an undesirable invasive plant) and not a coveted sugar maple. The yellow iris that appeared next to the pond is a thug called Iris pseudacorus. And I remember a near disaster when I was working around a free Angelica archangelica (I thought) and a gardening friend pulled me away—as if from an oncoming train—because it was a giant hogweed! So be careful—there is rarely a free, desirable plant.   There are exceptions to my cautionary approach, however. In my companion-style vegetable garden, where flowers and herbs are mixed among the vegetables, I have always allowed several volunteers to remain. Asters (Aster spp.), milkweed (Asclepias spp.), Shasta daisies (Leucanthemum x superbum), and seedlings from last season’s cleome (Cleome spp.), dill (Anethum graveolens), or love-in-a-mist (Nigella damascena) are all great for pollinators or other beneficial insects.   In the Coyne/DiNezza garden in Buffalo (a popular stop on the Snyder-CleveHill Garden View and AAA Motorcoach tours), the gardeners willingly permit Queen Anne’s lace (Daucus carota) to pop up intermittently, quite aware that removing them can be a chore. In this garden, their airy little heads, waving among traditional perennials, have become part of the Coyne/DiNezza garden’s signature.

Jim Lesch: Richard LeRoy and I converted several acres of former farmland in Scottsville to gardens. Behind our property there are still farm fields, hedgerows, and woods. From that reservoir, native plants come unbidden in their effort at succession back to forest. We find volunteer honeysuckle (Lonicera spp.) and dogwood (Cornus spp.) shrubs on a regular basis. We keep a handful of these at the edge of our property to blend visually with the hedgerows in the distance.   In the last five years, junipers (Juniperus spp.) have also appeared; these could be either volunteers from native junipers or our own ornamentals reverting to a parent juniper species. We have relocated and kept most of these. They are a bit rangy, but they do have an interesting bluish cast and tight columnar shape. To us they seem more vigorous and likely to survive on our alkaline soil than the named ornamentals we have introduced.   Besides the “volunteers” coming from the fields (and dandelions from our neighbors), some of our ornamentals also spawn volunteers. For instance, many of our maples have sown profusely. We removed a nearly mature Norway maple to end its invasive ways. A hedgerow of Amur maples (Acer ginnala) and a single paperbark maple (A. griseum) have reproduced widely and are thus weeds as far as we are concerned. On the other hand, we were delighted that one of our miniature Japanese maples (A. palmatum) seeded itself close by. We will dig and site it elsewhere or give it as a gift.

Tall verbena (Verbena bonariensis) can create a beautiful stand if allowed the space to reseed with abandon. Photo by Michelle Sutton

Tall verbena (Verbena bonariensis) can create a beautiful stand if allowed the space to reseed with abandon. Photo by Michelle Sutton

A few of our yews (Taxus spp.) seed themselves. We are often unsure whether the new plants are going to be spreading or upright yews, since we have both in our gardens. Pine (Pinus spp.) and spruce (Abies spp.) seeds also occasionally sprout. It is a joyous feeling to see Mother Nature doing so well on our reclaimed agricultural land, but often we cull these offspring to avoid ending up a forest rather than a garden.   Among perennial flowers that spread, the winners in our garden are undoubtedly the violets (Viola spp.). We remove literally four to six wheelbarrow loads from our planting beds each year. If we did not do this, many other perennials could not survive due to unrelenting competition from the violets.   The short woodland grasses and the Northern sea oats (Chasmanthium latifolium) we’ve planted have volunteered here and there and seem to cheerfully tolerate not just some shade, but dry clay. Last year we removed most of a stand of sea oats to make room for other plants, but we still have some to enjoy. We planted ajuga (Ajuga spp.) in partial shade. It kept sowing itself some feet away in the lawn. Over the years we have removed these volunteers several times to establish ajuga elsewhere.

Milli Piccione: I started gardening in earnest in my early 30s. My naive vision was that the gardens were going to be orderly, wellthought out, and totally under my control. After the first season of obsessed planting and weeding, I started to relax ‘just a bit’ and observe and appreciate the habits of my perennials and annuals.   I also began to realize that Mother Nature’s volunteers could sometimes be my allies, not my enemies. The first volunteer of note in my small woodland area was a magnificent biennial—the 5-foot-tall velvety foliaged mullein (Verbascum spp.). I learned that it attracted seed-eating birds and became a believer the next day watching nuthatches zipping up and down the matured flower stalk feasting on the seeds. What a delight!   As I became more experienced and more observant I left select volunteer perennials and annuals in place.In one little section of my rock garden I had planted the dwarf Solomon’s seal (Polygonatum humile) adjacent to a miniature narrow gold-leaved hosta (Hosta sp.). After two or three years, both started to travel and intertwine, forming an utterly charming combination. I’ve tried to recreate this effect in other gardens, the outcome never as successful as nature’s original. Self-seeded annuals and perennials can soften hardscaping as seeds, amazingly, germinate in the cracks and edges of walks and in dry-laid stone walls. The balance between a softening versus an unkempt look is in the vision of the gardener—your garden, your choice.   Self-seeded perennials don’t usually get out-of-hand. Annuals, however, can take advantage of your generosity. My favorites are forget-me-nots (Myosotis spp.), tall verbena (Verbena bonariensis), and nicotiana (Nicotiana sylvestris). These can work if you’re willing to cull them when necessary, especially when the volunteers have to ‘play well with others’. Forget-me-nots are a favorite harbinger of spring—the diminutive flowers form an exquisite pale haze underneath spring bulbs. About three weeks after they have finished flowering, the fresh foliage turns dry and nasty looking. Rip out every plant once the seed has ripened; as you pull the plants you’re automatically broadcasting seed for the following year.

Nicotiana (Nicotiana sylvestris) is one of garden designer Milli Piccione's most valued volunteer annuals. Photo by Milli Piccione

Nicotiana (Nicotiana sylvestris) is one of garden designer Milli Piccione’s most valued volunteer annuals. Photo by Milli Piccione

Tall verbena and nicotiana are 3 and 5 feet tall, respectively, and are both prolific self-seeders. Choosing which seedlings to keep depends on their neighbors and the final effect you want in your garden. The verbena is narrow with delicate purple flower heads that appear to float; it attracts monarch butterflies and other pollinators. Tall verbena is easy to tuck into existing beds, taking up little horizontal space. The opposite in its demands is the nicotiana—one plant can be 5 to 6 feet tall with 2-foot-long leaves and fragrant tubular white flowers. If you have the space they are magnificent as long as you are merciless when thinning, because they can easily shade out smaller plants.

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Natural Selections: Birches & Their Kin

by janem on March 17, 2014

Andrew Fowler

Story and images by Andrew Fowler

Birches (Betula spp.) are among the most cold-hardy of deciduous trees, being natives of the northern boreal forests alongside firs and spruces. During the glacial periods, birches remained close to the glaciers’ edges, and once those glaciers retreated birches became the pioneer species. Today they prove themselves good colonizers of disturbed soils, highway cuts and abandoned agricultural fields, and can serve as nurse trees for other species. They are usually short-lived, except perhaps for the yellow birch (B. alleghaniensis), which maintains its presence with beech and maple among climax forest communities along the Appalachian chain and throughout the northeast and Great Lakes.

Birches are noted for their colorful, peeling bark, with white being the most commonly associated feature. It was this asset that brought birches into the gardeners’ world—unfortunately, the European white birch (B. pendula) became the birch of choice, while the native species were all but ignored. The problem with most birches is that they are denizens of cold northern forests, and placing them in manicured landscapes and lawns is almost inevitably going to stress them. The European white birch soon proved to be highly susceptible to the bronze birch borer, a native beetle that feeds on the cambium of stressed trees and generally proves fatal. The native paper birch (B. papyrifera), also a white-barked species, is less susceptible to the beetle. However, this species likes a cool, moist acid soil, a rare commodity in most landscapes. The determining factor in bronze birch borer resistance is the presence of the chemical rhododendrol, produced in stressed and dying bark tissue in all white-barked species of birch, which is a strong attractant to egg-laying female borers. There are two native birches that do not produce rhododendrol and are thus resistant to the borer: the sweet birch (B. lenta) and the river birch (B. nigra). Leaf miners are also a major problem on white-barked species, but not for sweet and river birch.

All birches have alternate, ovate, pointed leaves with finely serrated margins on thin reddish-brown branches. Fall color is usually a golden yellow. All are monoecious with separate male and female flowers formed in the fall but remaining tight until spring. The female flowers are upright and enclosed in a bud. When open they look like small cones. Male catkins are pendulous and clearly visible through winter, looking like little tails hanging from the branch tips. Flowering takes place in April, when the catkins expand and open to shed the pollen, which is windborne and can be an allergen for some people. The seeds are small and winged and are dispersed during the winter as the small cones disintegrate.

Birches prefer moist acid soils that remain fairly cool. They have fibrous root systems, which makes for easy transplanting. Fall transplanting is not recommended, however, because their thin bark and abundant twigs make water conservation through the winter difficult. Transplanting in the spring before bud break is the best time. However, they readily sprout from the base if cut down, and can be rejuvenated this way.

Birches are “bleeders” and should not be pruned in late winter or spring, but rather right after leaf drop in the fall. They can be tapped in the spring for their sap, which is used to make birch beer. Often frozen sap can be found during the winter months hanging from storm-broken twigs, and these make good popsicles.

As mentioned above, the white-barked species are particularly prone to problems due to environmental stress, notably attacks by birch bark borer and birch leaf miner. However, there are two species, native to the eastern United States, which are fairly resistant to both pests. These are the sweet birch (B. lenta), also known as cherry birch or black birch, and river birch (B. nigra).


   Sweet BirchSweet Birch

Native from New York to Maine and down the Appalachian chain to Georgia, the sweet birch is hardy to Zone 3, and is better adapted to cultivation in warmer climes than the white-barked species. This species is a fast grower and reaches a height of perhaps 50’ and a span of 35’, and is distinctly upright in youth. The bark is a rich red-brown with prominent horizontal lenticels, reminiscent of cherry bark, becoming almost black and scaly with age. The young stems are thin and reddish brown and strongly smell and taste of wintergreen when bruised or chewed, which makes for easy identification. Yellow birch (B. alleghaniensis) also has a wintergreen odor but is not nearly as strong. The leaves of sweet birch are ovate, sharp pointed and finely serrated. Glossy green in summer, they turn a rich golden yellow in the fall, perhaps the best of all the birch leaves for fall color. The male flowers form in the fall and persist through winter hanging from the terminals, expanding and opening in April before or with the unfurling leaves. The pistillate flowers are held upright lower on the branches and open in time to receive pollen in the spring. The pistillate flowers develop through the summer into strobiles, resembling small cones, holding the small winged nutlets, which are dispersed through the winter.

This species does well on moist, fertile, acidic soils with good drainage, but will also tolerate dry soils once established. Full sun is best but it will also tolerate a modicum of shade. Poorly drained soils should be avoided.

The lack of papery, peeling bark has relegated this species to obscurity, resulting in a complete lack of cultivars, but I find it has a charm of its own, and certainly has the best fall color of any birch. It is definitely worthy of more attention.

River birch barkRiver Birch

The river birch is the only birch native to the warmer regions of the eastern United States, ranging from Massachusetts to Florida and west to Texas. It is a denizen of riverbanks and floodplains subject to periodic flooding. This makes it a good choice for wet areas of the landscape, but the species can also tolerate dry soils, at least for short periods. Its heat tolerance also makes it more easily incorporated into urban landscapes. Soils should be on the acidic side, or chlorosis can develop. The bark of this species is creamy and shiny on young stems, becoming papery thin and peeling off in curls, revealing pinkish and orange red patches underneath. It is perhaps the most colorful of the birches. The leaves are wedge-shaped, coarsely serrate or lobed, and pointed. The fall color is yellow, but is rather dull compared to the sweet birch, and the leaves often drop very early. It grows quickly to a mature height of about 60’, being pyramidal in youth. It is commonly multi-trunked, which serves to show off the bark.

Because of the widespread adaptability of the species, there are a number of cultivars now available. Probably the most frequently encountered is Heritage® (‘Cully’), which is a patented selection from Heritage Trees Inc. of Illinois. It displays increased vigor, with larger, glossier leaves and whiter bark than the average river birch. Other notable cultivars are Fox Valley® (‘Little King’), a compact, bushier grower to about 15’, and ‘Shiloh Splash,’ a variegated shrubby form to about 10’, with white edges to the leaves.

Like sweet birch, river birch is essentially immune to birch bark borer and highly resistant to leaf miner, and makes an excellent landscape specimen. Of course, as with any monoculture, the more they are planted, the more likely a pathogen is to appear. Diversity in the landscape is the key.

There are a few other members of the birch family (Betulaceae) worth considering for the garden. These include hornbeam (Carpinus spp.), and hophornbeam (Ostrya spp.).

Hornbeam in FallAmerican Hornbeam

The most common hornbeam in landscapes is the European or common hornbeam (C. betulus). Long used in Europe for hedges and screens, it takes pruning very well and is sometimes pleached into pergolas and arbors. It retains its brown dead leaves through winter, like the European beech (Fagus sylvatica), thus adding to its value as a screen. The fastigiate varieties are also highly prized. The native American hornbeam (C. caroliniana), on the other hand, is virtually ignored by the gardening public, while offering many of the same features as the European species. Native to the eastern half of the United States from the Great Lakes to Florida and hardy to Zone 3, the American hornbeam also goes by the names musclewood, blue beech and ironwood. An understory species of wooded lower slopes and floodplains and commonly associated with witch-hazel (Hamamelis virginiana), it is usually a multi-stemmed tree that can reach 30’, but can be trained as a single trunk. The stems have a fluted sinuous look, resembling well-muscled arms, and the smooth blue-gray bark accentuates this. The leaves are ovate and pointed with a doubly serrate margin. New leaves tend to be bronzy to reddish, becoming dark green in summer and turning yellow, orange and red in the fall. It has better autumn color than the European species, but does not hold its dead leaves through the winter.

The male flowers are in catkins hanging from the tips of twigs, like birches. Female flowers are low on the branches and are short, each ovary set in a papery three-lobed bract. These become nutlets arranged in a hanging infructescence, 2 to 4” long, which resemble hop fruits. The fruits gradually disintegrate through winter, spreading their papery seeds.

Hornbeam barkThe wood is very hard and was used to make tool handles and mallet heads. It can be polished very smooth to resemble horn. The name hornbeam probably derives from this characteristic, while “beam” comes from the German word “baum,” meaning tree.

Hornbeams like deep moist acidic soils, even seasonal wet sites, but can adapt to drier soils and those with a higher pH. Although shade-growing in nature, they can also grow in full sun, where they will be much fuller branched. Generally, they are pest-free, although fusarium cankers can be an issue with stressed trees. They have a deep, coarse root system, consequently fall transplanting is not recommended; springtime is best. A delightful small native species, the American hornbeam deserves more attention from gardeners.

 

 

 

Hophornbeam barkAmerican Hophornbeam

In the same woods as the American hornbeam, in the higher, drier slopes, the hornbeam disappears and American hophornbeam (Ostrya virginiana), the other ironwood, appears. Covering the same geographic range as the hornbeam and hardy to Zone 4 (possibly 3), the hophornbeam is usually a single trunk, growing straight and tall to about 40’. Unlike the smooth gray bark of hornbeam, the bark of hophornbeam is shiny dark brown on young stems and shaggy gray on older trunks, which makes for easy identification. The leaves are similar to birch and hornbeam, although a little wider, with doubly serrate edges. The fall color is a muted yellow and rarely effective. The flowers are like those of the other species discussed, with male catkins, grouped in threes, hanging from the tips and smaller female flowers hidden below in the foliage. In the fall, a nutlet is formed, enclosed in a papery pod, several being strung together to resemble the fruit of hops; hence the common name. These dry and persist through much of the winter and can also be used to identify the tree. The fruits have tiny hairs, which can irritate the skin.

Like the birches and hornbeams, the hophornbeam is a bleeder, so pruning should be done in fall or winter. Like most trees, moist acidic soils are preferred, but the hophornbeam can also tolerate dry soils. It’s a tap-rooted species, so container-grown trees are easier to establish. Full sun will produce a dense canopy, while in shady situations an airy open structure is more usual. The wood is extremely hard and strong, resistant to ice storm damage, and has been used for making airplane propellers and sleigh runners. Hophornbeam makes for a tough, dependable small tree, with very few pest problems

The birch family provides opportunities for most garden situations, from dry shade to open sunny areas and even wet soils. Winter interest is available in the colorful barks of some species and the hanging catkins. Fall colors come in reds, oranges and yellows. The fruits of these species provide food for small birds, such as chickadees, and small mammals.

Andrew Fowler operates Holmes Hollow Farm nursery and Christmas tree farm in Victor, NY.

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