Crossing the Line: When Plants Become Invasive

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Athyrium nipponicum ‘Pictum’ grows with English ivy. Ivy is considered a highly invasive plant.

There is a long history of botanists and horticulturalists traveling around the world in search of new, beautiful and useful species of plants.  It is an essential part of our nation’s history to both send native American species to Europe, and to seek out and grow imported species here. 

You’ll hear wonderful stories of early colonists risking their lives and freedom to bring back some rice, or a tea shrub, or some other potentially productive and lucrative plant encountered on their travels, to put into production here in the ‘New World.’  Tony Avent of Plant Delights near Raleigh is one of many contemporary horticulturalists still importing new plants from elsewhere.

One of the trees imported from Asia was the white mulberry tree, Morus alba.  They were supposed to form the beginnings of a silk industry here in Virginia.  Sadly, the silkworm industry never took off in Virginia.  Worse, the white mulberry became an invasive species, even hybridizing with our native red mulberry.  But who knew that would happen in the Eighteenth Century?

Another Asian tree imported during the Colonial era, to potentially support silkworms, is the paper mulberry, Broussonetia papyrifera, formerly known as Morus papyrifera.  You may have noticed these odd-looking trees lining Francis Street near the Colonial Capitol building.  They are not considered invasive, but the silkworms didn’t care for them.  In China, they were used in the production of early paper products.

It may take only a few decades for a wonderful new plant introduction to cause enough problems in its new environment to find itself reclassified as an invasive nuisance plant. The very qualities that make a new introduction exciting and marketable may also make it harmful to its new ecosystem.

Read more and see more photos of Virginia’s invasive plants on Our Forest Garden. All new posts now go to the new website. Have you followed it, yet?

See Virginia’s Invasive Plant List

Blossom XXXVIII: Akebia quinata

Akebia quinata

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Chocolate vine, Akebia, grows joyfully in a corner of our garden.  It springs back to life early in the season, when many of our other woodies are still resting.  First, the delicate spring green leaves emerge, clothing the long and twisting stem with fresh growth.  Compound leaves emerge in groups of five leaflets, which is how it earned its species name, ‘quintata‘.  And then its beautiful rosy flower buds appear, opening over a long season of several weeks.

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I mail-ordered this ‘chocolate vine’ several years ago to clothe a new arbor we were installing.  I’d never grown it before, and never admired it growing in another’s garden.  But I’m always interested in trying new things; especially unusual fruits.    This vine is supposed to produce an edible pod that tastes like chocolate.

And I only ordered one, not the two necessary for pollination, to first determine whether it would grow well for us.  Does it like our climate?  Will the deer eat it?

Yes, and no.  And from that first bare root twig, it has taken off and begun to take over this corner of the yard!  Yes, I could prune it into better manners.  But I rather like its wild sprawl through the neighboring trees.

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But as much as the vine extends itself, it doesn’t appear to pollinate itself.  We’ve not yet found any edible pods to taste.  I could plant another vine to see if I can make them produce fruit, but that would be unwise. 

Akebia grows so robustly that it can smother out other nearby plants.  It is considered invasive in the mid-Atlantic region and has made the list of regulated invasive species in Kentucky, South Carolina and Georgia.

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We enjoy this vine for its flowers.  It is simply stunning in bloom, filling its real estate with bright flowers.  There are plenty of little dangling stems to cut to add to flower arrangements.

I’ve never noticed this vine growing in the wild in Virginia, and have not heard of it being a problem in native habitats in our area.  It is something of a novelty to us.

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In its native Asia, where both the pulp and the husk of the fruit are enjoyed in cooking, the vines are cut and woven into baskets.  The vines wrap themselves in neat spirals around their supports, laying themselves in parallel layers like a living sculpture.  Akebia was first imported to the United States as an ornamental vine around 1845.

Akebia is a beautiful plant, and you can find it from several good mail order nurseries in the United States and the UK. You will even find named cultivars.   It tolerates shade, is drought tolerant, and grows in a variety of soils.  This deciduous, woody vine is hardy in Zones 4-10.  The color of its flowers blends well with other springtime flowers in our garden.

Ironically, the more resilient and adaptable a plant, the more likely it will eventually make it on to a list of ‘invasive’ plants.   Although this spreads and roots at the nodes, I feel confident that the birds won’t spread it elsewhere, since our vine isn’t producing fruits and seeds.

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I would plant Akebia again, given the opportunity.  It is a useful  vine to cover a trellis, pergola, fence or wall.  But use it with caution, and do keep the secateurs handy.

I’ll need to give ours a trim this spring, when the flowers have faded, to keep it in bounds.  That said, some of those trimmings will be rooted and shared with gardening friends.

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Woodland Gnome 2018

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Blossom XXXVII: Daffodils, Variations On A Theme

Blossom XXXVI: Crocus

Blossom XXXV: In The Forest

The Arum Affair

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My new-found friends at the Native Plant Society might not approve, but I’m still falling in love with this beautiful Italian Arum.   After six days under the snow, with temperatures falling near zero at night, it still looks this fresh and crisp as the snow melts around it!

Arum leaves hold their vibrant green throughout the winter, as though unaffected by the ice and freezing cold.  The beautiful geometric patterns traced on their leaves in softest cream remain elegant from autumn through to early summer.  They remind me a little of a cold hardy Alocasia.

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Arum growing with our daffodils last February

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Native to Southern Europe and North Africa, Arum originated in a much warmer climate.  But it has a superpower: Arum italicum is thermogenic, capable of producing heat from its leaves and from its unusual flower.  The mitochondria in each cell produce excess heat, which gives the plant some protection from the cold.

A member of the Araceae family, it also has calcium oxalate crystals in its leaves.  These crystals are very irritating to skin and soft tissue… like the tender mouths of hungry deer.   All parts of the Arum are poisonous, including the corm from which it grows; which is the other reason I love these beautiful foliage plants.

Deer, squirrels, voles and rabbits won’t touch them.

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Columbine emerges through a winter ground cover of Arum italicum last March.

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These are a useful ground cover species in our woodland garden.  They grow best in shade and though drought tolerant, grow more prolifically in moist and fertile soil.

While I am thrilled to see these beautiful plants spread through our garden by seed and division, their prolific growth and nearly indestructible nature make them problematic in other regions of the United States.  Areas like the Pacific Northwest consider them invasive and ask home gardeners not to plant them.

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But Arum remain my cold-weather guilty pleasure.  I ordered over 200 of them this fall from Brent and Becky Heath, sharing a little more than half with my gardening friends.

I’ve planted them in beds and pots, beneath shrubs and amongst spring bulbs.  Interplant them with Hosta to keep a beautiful foliage presence in your Hosta beds year round.  Pair them with either hardy or deciduous ferns for delicious spring time associations.

I use them in parts of the garden where we grow Caladiums in the summer.  As we lift the Caladiums in fall, the Arum emerge from their summer dormant period.  Arum die back in early summer as the Caladiums fill in.

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Exotic as they may be, Arum still fill a niche in a North American woodland garden.  They hold and protect the ground against erosion.  They produce both nectar and pollen for pollinators each spring.  Birds eat their seeds in mid-summer.  And, their beautiful leaves make this gardener very happy. 

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Brent and Becky Heath’s display gardens in Gloucester, VA,  feature many blooming shrubs, including this lovely Camellia. The Heath’s call Arum italicum a ‘shoes and socks’ plant because it works so well as a ground cover beneath shrubs.

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I’m still wavering up and down the native plant/exotic imported plant continuum.  I’m hanging out more these days with the native plant enthusiasts and reading the literature.  I understand the nativist point of view, and yet I still believe that there is space in our garden for a population of exotic ‘come here’ plants, too.

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How would I garden without our Camellias and Rhododendrons, Alocasias, Narcissus, Caladiums and Mediterranean herbs?

Basically, if it will grow here and not end up as breakfast for a deer, I’m willing to entertain most any plant for at least a season or two.  And when it makes me happy, I just might explore a more lasting relationship.  Which perhaps explains the Arum affair….

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Arum italicum blooming in our garden last April

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Woodland Gnome 2018

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High Strangeness

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Do you know this plant?

What would you think were you to find this emerging from the Earth sporadically all over your garden?

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This is absolutely one of the strangest things I’ve encountered in this terribly odd Forest Garden we tend.

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There is a bamboo grove at the bottom of the back garden, growing out of the ravine, which sends up new shoots of bamboo each spring.

We try to keep it in its bounds, but that is sort of like keeping an English Setter puppy on its leash at the beach.  If you’ve raised a  hunting dog, you know exactly what such creatures do.

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And this bamboo, in its exuberant spring growth, sent up this massive shoot more than 20 feet from the established stand of bamboo.  Look at its massive girth!  It came up right at the base of a young fig tree, in the midst of a sage plant.  And as if that weren’t enough, there was no sign of this bamboo when I was last tending this bed on Sunday.  This appeared between Sunday afternoon and Wednesday afternoon.

We realize now that the bamboo has sent its roots and runners underneath this entire area in the lower garden.  We found other, smaller, shoots coming up in several places far and wide from our “Bamboo Forest.”  A Japanese friend told us we can eat them, but we still have not.  We remove them, marvel at them, and compost them.

When I removed this one today, I was surprised to notice how large the empty cavities are within the stalk.  These cavities, separated by thin membranes,  contain water.  Bamboo is a most useful plant.  And I am sure in regions where it is regularly harvested and used, it is very desirable.  Our particular variety quickly grows to the height of a tree, more than 40 feet tall, in a few weeks.

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Plants become invasive when they upset the balance of life in an area.  When they grow unchecked, taking over the territory needed by other, weaker plants, then they cause a problem.

Many of us don’t think ahead far enough to realize that the beautiful plant we bring home to our garden may one day take over and become an invasive nuisance.  We often barely even consider the mature size of a plant, let alone what may happen with it decades down the road when its seed and roots have spread far beyond where we originally intended for it to grow.

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Our ancient grove of native Mountain Laurel

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Many plants, like ivy, take a few years to get established.  Then once they have grown a large system of roots, they suddenly take off, surprising you with their rampant growth.

My day has been spent in the garden today. 

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A lovely Azalea, planted long ago, nearly swallowed by the shrubs and trees which grow around it now.

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One of my beloved gardening sisters invited me to dig ferns from the steep slope behind her home.  She’s been weeding and tending the slope for long enough now that the ferns have begun to take over.  She has at least six different varieties naturalized, and called me to share in the bounty.

I’ll show you more of that adventure tomorrow, and some of the beautiful ferns she gave me.

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Two of the ferns growing in my friends’ garden. I dug tiny starts of both of these varieties.

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My task, once home, was to clean up the shady bank where I wanted to plant them.  More invasive plants gone wild:  honeysuckle and wild strawberry vines, clumps of grass, unknown yellow flowering weeds, and more had to come out before I tucked the new ferns into moist shady Earth where they may grow and spread.

One man’s weed is another man’s wildflower, so they say.  Gardening is always about making choices about what may grow and what must go!

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Some of the newly planted ferns are visible lower right, dovetailing into the fern garden we’ve been working to establish for the last five years.  The new Rhododendron is just visible top, center. This area is cut with a path.

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But whether “desirable” or not, plants serve their purpose in the garden community.

As I was pulling tall “weeds” from around another fern bed today, there was a beautiful painted turtle hiding in their moist shade.  Those weeds were his mid-afternoon shelter.  He probably eats the insects drawn to them, or perhaps some part of the plant itself.  I quietly left off pulling in that area, and moved on elsewhere to leave the turtle in peace.

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The Rhododendron I brought home in February has finally bloomed! Some may find these electric purple flowers highly strange…..

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Our gardens are always full of high strangeness, when we take the time to observe.  We may find an unusual insect, a new bird, or a beautiful flower in bloom.

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It is never the same from one day to the next, which is why the garden endlessly fascinates me.

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Re-blooming Iris, “Rock Star”

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Woodland Gnome 2015

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Surrounded by Reeds

 

Our creeks, marshes, and ponds lie surrounded by thick stands of reeds.

Reeds are a very large, very tough, very long lived grass.    Found in temperate and tropical wetlands across much of the planet, they have their uses.

But like any grass, they grow from extensive mats of roots and rhizomes, creeping along in the mud.

Some of our reeds are native plants. 

 

Known as Phragmites australis, subspecies americanus;  the native reeds grow across our entire continent from southern Canada south to the Mexico border in the west.

Here on the east coast, they grow as far south as our border with North Carolina.

Another species, possibly native, grows along the Gulf coast.  Phragmites australis subspecies berlandieri may have crept northward from Central and South America at some point.  It has now moved westward and is found in parts of Arizona and California.  Items made from reeds, found in archeological digs in the American Southwest, date to over 40,000 years old.

 

Our native species co-exist with other marsh and aquatic plants.  They were used by Native Americans for food, shelter, and to make useful things.   Every part of the plant is edible.  Spring shoots may be harvested and eaten like bamboo shoots.

But another, hardier species of reed, Phragmites australis, was brought to North America by European ships in the 18th and 19th centuries.  Like so many “exotic” species, it has become invasive, choking out other species which at one time grew along our waterways.

Phragmites australis grow across much of Europe, North Africa,  and the Middle East.  They are an ancient species.  In their own native areas, they aren’t invasive.  And they have been used for many purposes for thousands of years.  But transplanted to North American waters, they behave differently.

Why should we care about which reeds grow along the creeks and in the marshes?

It all comes down to biodiversity.

 

When lots of different types of plants grow together in a community, many types of animals find food and shelter.  A greater number of species can live together in harmony in a place.  Their relationships are rich and complex.  The whole community becomes stronger and better able to withstand fluctuations in climate.  The ecosystem remains in balance.

When an invasive species gets a foothold, it often grows stronger and faster than the native species it replaces.  It has fewer animals which use it.  Soon the invasive species takes over, creating a monoculture, spreading, and changing the community so that fewer species can live in that place.

And that is exactly what is happening to our waterways across much of the United States.

The area where we live, around the Chesapeake Bay, is one of the few areas in North America where the native species of reed still lives.  And the natives are crowded out, more each year, by the invasive Eurasian reeds.

Now, these reeds, known as Phragmites (pronouced “frag-mahy-teez“), gobble up real estate along waterways.  They can grow to  over 15” tall.

 

Like bamboo, their system of underground roots and rhizomes grow many feet each year away from the clump, to cover new territory.  These roots and rhizomes grow many feet deep below the surface.

At the surface, stolons, or horizontal stems, grow many feet each year.  New plants emerge at each joint in the stolon, and each of these new plants sends down new roots.  The result is a very dense, thick mat of growth at and below the surface.

Thick, dense vertical growth of the actual grasses grow anew each spring.  They are so dense and so tall that they shade out any other plant which tries to grow in their midst.  The stems of each plant are hollow.  Large leaves grow at nodes along the length of the stem, much like the leaves on a stalk of corn.  The plant is crowned with a very large plume of flowers, which produce thousands of seeds each season.

It is easy to see why these Phragmites spread so quickly!  They not only spread out with their rhizomes and stolons each year;  but those seeds travel by air and water to colonize new areas.  Very few species of birds use the seeds.  Very few species of animals make their homes among the Phragmites in a marsh.  And currently, we aren’t harvesting and using these reeds in any substantial way.

Phragmites die back each winter, but are perennial and re-emerge each spring.  The previous year’s stalks stand all winter long.  Silt accumulates around them, and the water becomes progressively shallower each year.  They eventually form a wall between the shoreline and the water, blocking the view and creating a dense barrier for anyone trying to access the water for fishing or boating.

Invasive Phragmites emerge early in the spring, before the native species and before many other aquatic plants.  They grow taller and with more vigor than our native  Phragmites australis, subspecies americanus.

They have grown into a hot topic of debate among those of us who live along the waterways they choke.

Many would like to get rid of them.  But from what you now know about Phragmites, you probably understand why this is difficult and expensive.  Their extensive root system allows them to regenerate after harvesting or burning.  They must be burned for several years in succession to eventually destroy the roots.

There is experimentation with herbicides.  But how will broadcast herbicides affect the birds, fish, amphibians, reptiles, and other plants living in marshes and shallow creeks?  Herbicides are a  controversial solution.  Permits are required, and the herbicide must be sprayed during the period of active growth in late summer or early fall.  The sprayed herbicides will travel, like the Phragmites’s seeds, in the air and water for many miles.

And who will pay for the herbicide, even if a community decides to go that route?

This is one of those slowly creeping problems which eludes an easy fix.

But Phragmites, though invasive, remain a useful plant. 

They are sometimes planted to filter and clean waste water.  They help catch run-off, trap harmful chemicals in their biomass, and remove other waste products so the water can be used again.

Phragmites also filter our air.  They filter excess carbon from the air, using it to grow.  Carbon, a major greenhouse gas, is removed from the air and returned to the soil through their efforts.  While filtering carbon, they also remove other polluting gasses from the air we breathe, releasing pure oxygen and water vapor.

Phragmites stop erosion.  Because they grow in any moist soil, they can hold areas which might otherwise erode from run off , tides, and flooding.  They can tolerate brackish, salty, or fresh water.  Tidal flooding doesn’t bother them.

These are wonderful plants with many uses and benefits.  We don’t value them because we no longer need them as a natural resource for making things.   We no longer eat them as a staple of our diet.

As with so many things, it is our own point of view which defines “nuisance” as opposed to “resource.”

Perhaps the solution to our problem can lie more in creativity and less in destruction of the growing world around us.

 

Words and Photos by Woodland Gnome 2014

 

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For More Information:

Phragmites Field Guide

Invasive Species of the Chesapeake Bay

Guide to the Control of Phragmites, Maryland Department of Natural Resources