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Plants Behaving Badly: Aggressive vs. Invasive

July 28, 2019

tradescantia in bloomAs terrestrial invasive plants have become a more prominent issue, I’ve noticed that many gardeners are confused about what makes a plant “invasive.” Part of the confusion is that gardeners have long used the word “invasive” to refer to plants that behave badly in their gardens. Gardeners also call them “garden thugs,” these plants who don’t play well with others. Whether you invited them into your garden or they showed up uninvited, they quickly shouldered others aside and hogged more than their fair share of garden real estate. But this is not what scientists mean when they call a plant “invasive.” So, to help clear up the confusion lets refer to these plants that behave badly in the garden as aggressive.

Invasive refers to how a plant behaves when it escapes from your garden. To be defined as invasive, a plant has to meet three criteria:

  1. An invasive plant is a non-native plant. Native plants have coevolved with other species (plants, animals, insects, fungi) in our native ecosystems and have long-standing relationships of interdependence with those other species that provide a system of checks and balances. This means that, although a native plant like spiderwort (Tradescantia virginiana) may behave aggressively in the garden, self-sowing rampantly and spreading itself around where it is not wanted, it will not create a problem in the wild.
  2. An invasive plant has naturalized in the wild. This means that the plant is growing where no human being planted it and that the plants are reproducing on their own and spreading in wild places.
  3. A plant is invasive when the naturalized populations of the plant in the wild are causing harm. This usually means harm to native ecosystems because the plant is out-competing native plants for light, water, nutrients and space, creating ripple effects through all the species in the ecosystem that were dependent on the native plants that have been crowded out.

Some plants that behave badly in the wild also behave badly in your garden (they are both invasive and aggressive). A good example is goutweed or bishop’s weed (Aegopodium podagraria). But many plants that seem perfectly well behaved in your garden (not aggressive) create havoc in the wild when they escape from gardens. This is why it is so important to understand the difference between an aggressive plant and an invasive plant. I’ve often heard gardeners arguing that a plant is not invasive by saying, “I’ve had it in my garden for years and it has never spread,” or “If you just keep it pruned, you can keep it under control.” But these assertions focus on how the plant behaves in your garden, not on the chance that it will escape and behave badly in the wild.

Most documented invasive plants in Maine have escaped from ornamental plantings, usually through having their seeds dispersed far from the parent plant by wind or by animals. It’s not just coincidence that many of our most problematic invasive plants have bright berries that are attractive to birds. The birds eat the berries, the seeds are roughed up and prepared for germination as they pass through the bird’s digestive system, and the seeds are then pooped out far from the parent plant, enclosed in a nice little packet of fertilizer to give them a good start in life. The gardener growing the parent plant usually has no idea that the plant has escaped from their garden.shrub honeysuckle berries

There’s a good reason why states adopt lists of invasive plants; landscapers, homeowners, and gardeners are usually not good judges of how likely it is that a plant will escape from an ornamental planting and behave badly in the wild. (To see the Maine list of invasive plants, click here.)

Bottom line: Aggressive (how a plant behaves in your garden) and invasive (how a plant behaves when it escapes from gardens) are not the same thing, and we can’t predict the likelihood that a plant will escape from our gardens and behave badly in the wild from how it behaves in the garden.

Gathering Energy: GBBD, July 2019

July 16, 2019

daylily budsIn mid-July, my Maine garden is in transition. The big flush of early summer blooms – Siberian irises, peonies, Amsonia, Baptisia, and the first flush of rose blooms – have faded, but the big high-summer show of blooms has not quite begun. It is as though the plants are gathering their energy, and all the buds about to burst into bloom are the evidence of that energy.

The daylily bloom that is the highlight of my garden in high summer has been slow to get started this year; most plants are about a week behind last year’s bloom times. But the same cool, wet spring that has delayed daylily flowering seems to have produced an abundance of buds. A few varieties have already begun to bloom, and others look as though they will bloom very soon.

buds about to open1 buds about to open2

While I’m waiting for the daylily show to begin in earnest, there are plenty of other blooms to enjoy.


This is the time of year when the flowers of Spirea japonica ‘Magic Carpet,’ goatsbeard (Aruncus dioicus) and astilbe spill over the retaining wall in the back garden. retaining wall spillover
entrance garden spirea In the entrance garden by the front door, the flowers of Spirea ‘Magic Carpet’ are fading, to be replaced by the hot pink flowers of Spirea bumalda ‘Neon Flash.’

front slope planting 2019On the front slope, which was planted in September, the plants still look miles apart. This was designed as a hot-color planting. Right now, it is dominated by the yellows of three species of coreopsis (C. verticillata, C. grandiflora, and C. lanceolata) and false sunflowers (Heliopsis helianthoides), with hot contrasts being provided by the red flowers of beebalm (Monarda didyma) ‘Jacob Cline,’ the eye-popping magenta of poppy mallows (Callirhoe involucrata), and the first blooms of purple coneflower (Echinacea purpurea).

Front slope plants July 2019

Asclepias tuberosa buds Oranges will soon be joining this mix as orange daylilies and the flowers of butterfly weed (Asclepias tuberosa) open.

There are some cool spots in my garden at this time of year.

The Blues Border beside the front door features cool blue shades of Tradescantia virginiana (spiderwort). blues border tradescantia
lavender walk 2019 Blue spikes of Lavandula augustifolia ‘Hidcote’ and ‘Munstead Strain’ are blooming along the Lavender Walk.
And a few beautiful spires of delphinium ‘Cobalt Dreams’ are gracing the back of the Blue and Yellow Border Cobalt Dreams

As July continues, these cool blues will yield to the vibrant colors of daylilies. I leave you with the advance guard of the daylily parade, the five varieties that were blooming when I took photos yesterday. (By this morning, four more varieties had joined these, and I expect a few more each day for the next week or two.)

early season dayliliesGarden Bloggers’ Bloom Day is hosted on the 15th of each month by Carol at May Dreams Gardens. Visit her blog to see the dizzying variety of flowers blooming at this time of year.

Early Summer in Maine

June 24, 2019

Pink patio bloomsLate June may be my favorite time of the year in Maine. Today was a perfect late June day, with clear blue skies, temperatures in the seventies (F), soft breezes, and long hours of light.

Side slope June blooms 2019By this time in June, we have made the transition from late spring to early summer. In my garden, plants that got off to a late start this year are making up for lost time. The garden looks lush and fresh, and it is full of beautiful flowers and of possibility. (Peak bloom here won’t happen for another month.)

back slope irises 2019Siberian irises, which are now at their peak, have been exceptionally prolific this year; all that spring rain made them happy. Most, like these that have self-sown down the back slope, bloom in various shades of blue. The side slope display also includes some white ones (‘White Swirl’), and this lovely wine color flower of ‘Carrie Lee’ is blooming in the deck border.

side slope irises Carrie Lee 2019

circular bed pastelsAt this time of year, the garden blooms primarily in shades of blue and pink, with the low contrast giving a feeling of lovely calm. The circular bed at the turn into my driveway is a study in pastels.  The blue and yellow border is in its blue phase, with contrasting yellows still to come.

blue and yellow blues

Biokovo with bumblebeeWith such a bounty of late June blooms, pollinators are plentiful and busy. As I walk through the garden, I see several types of native bees, bee-like flies, hummingbirds, and several species of butterflies. The bumblebee queens have been exceptionally numerous and large this year; they look a bit like flying school buses!  Among the early summer butterflies, the tiger swallowtails are the showiest. I love the way a pair of them will circle round one another in a spiral ascent up into the trees. They have been visiting many different flowers, including Siberian irises and allium. I managed to capture this pair nectaring together at a clump of Allium ‘Globemaster.’


Iris with swallowtail 2019 Globemaster balls with swallowtails

In late June, I feel as though I’m living in a lovely dream.

June patio blooms

Springing Into Summer: GBBD, June 2019

June 15, 2019

spilling rhododendron flowersBecause of our long, cool, wet spring, my Maine garden is lagging behind where it would normally be in mid-June and is just beginning the transition from late spring to early summer blooms.

My big sprawling rhododendron on the back slope would normally look like this about two weeks earlier; its flowers are just starting to fade. Other spring flowers that are still blooming include bluets (Houstonia caerulea) and moss phlox (Phlox subulata).

bluets still blooming moss phlox June

There are still quite a few flowers on the wild strawberries (Fragaria virginiana), but they’ve now been joined by their frequent companions, the later-blooming dwarf cinquefoil (Potentilla canadensis).

strawberries still blooming strawberry and cinquefoil

The flowers of the lilacs (Syringa vulgaris) are fading fast, but the roses have begun to bloom.

lilac fading Rose Therese Bugnet

weigela bloomingAmong the shrubs I added to my garden last year, the Fothergilla and the pinkshell Azalea (Rhododendron vaseyi) have finished blooming, but Weigela ‘Alexandra’ has just begun, and the maple-leaf viburnums (Viburnum acerifolium) are loaded with buds.

When I look around, I see so many plants about to burst into bloom. Along the walkway to the patio, the flower spikes of Heuchera x ‘Raspberry Regal’ have just begun to open. When they are fully open, these will be a magnet for hummingbirds, and I saw my first ruby-throated hummingbird of the season checking them out today.

raspberry regal opening raspberry regal flower spike

Other flowers that have begun to bloom this week include creeping thyme, Dianthus x ‘Firewitch,’ Tradescantia virginiana ‘Zwanenburg Blue,’ and Lady’s mantle (Alchemilla mollis).

creeping thyme firewitch
first tradescantia flowers alchemilla flowering

I am thrilled to have our native sundial lupines (Lupinus perennis) blooming on the front slope. I planted these from seed last year. Today, the first of the Siberian irises (Iris sibirica) opened, two weeks later than last year. These plants have loved all our spring rain and are loaded with buds. They should provide a lush display in the next couple of weeks.

Sundial lupine2 first siberian irises 2019

The display of hardy geraniums is also just beginning. So far, two varieties of G. maculatum, G. sanguineum, and G. x cantabrigiense ‘Biokovo’ have begun to bloom; but there are many more yet to come.

Early geraniums

Garden Bloggers’ Bloom Day is a virtual garden party hosted on the 15th of each month by Carol at May Dreams Gardens. Visit her blog to see a dizzying array of June blooms from other bloggers’ gardens.

Slowly Springing: GBBD, May 2019

May 17, 2019

daffodils 2019Spring in Maine is usually a flash in the pan, but unseasonably cold temperatures this year have brought us an unfolding so slow that it is sometimes imperceptible. But when it seems as though nothing is happening and spring will never arrive, I look around and realize that a lot has changed in recent weeks.

entry garden new growth side slope new growth

All over my garden, ground that was mostly bare a month ago is now mostly covered with new green growth. When I look up, I can see that the deciduous trees are starting to sport the lacy look they get when fading flowers combine with new leaves.

spring new leaves

In my garden, the crocus and hyacinth flowers have now faded, but daffodils are still in bloom. The little slips of forsythia that I transplanted outside my study window five years ago have finally gotten big enough to make a cheerful yellow display.

forsythia light yellow forsythia strong yellow

And as these flowers fade, the little pin cherry tree (Prunus pensylvanica) nearby is just beginning to bloom.

This is a season for spring wildflowers, both in and out of the garden. The lovely bluets (Houstonia caerulea) are blooming, and the sweet white violets (Viola blanda) have begun to open.

bluets 2019 sweet white violet

Along my rural dirt road, I see flowers of Epigaea repens (known locally as “mayflower” and further south as “trailing arbutus”) and of Viburnum lantanoides.

wild mayflower wild viburnum flower

Although only a few spring flowers are currently blooming in my garden, there are many promises of blooms to come once seasonably warm weather gets here.  There are fat buds on the rhododendron that covers the back slope with its flowers each May, on the lilacs along the front of my property, and on the maple-leaf viburnums (Viburnum acerifolium) planted last year. And in the new front slope planting, moss phlox (Phlox subulata) plants are showing tips of hot pink flowers about to open. spring flower buds

Garden Bloggers’ Bloom Day is hosted on the 15th of each month by Carol at May Dreams Gardens. Visit her blog to see what other gardeners have blooming in May.

Spring Clean-Up

May 2, 2019

April crocusesApril was the month for spring clean-up in my garden. I do little garden clean-up in the fall. Autumn is a busy time of year for me, with garden projects to be completed and firewood to be stacked; so, unless I have some disease or pest problem that demands action, I take in garden furniture, containers, and plant supports and leave the rest for spring.

Several inches of new snow in the first ten days of April delayed the start of spring clean-up, but by mid-April, flower beds were emerging from under the snow. As they did so, I got to work cleaning them up. (Because I live and garden on very sandy soil, I don’t need to worry about soil compaction from working in wet garden beds.)

deck border before 2019 deck border after 2019

I find spring clean-up a very satisfying activity. You start out with a messy tangle of stems, debris and matted leaves and end up with areas of bare soil and fresh shoots of new growth.

back slope before 2019 back slope after 2019

After a long winter, that new growth is a welcome sight. I never get tired of the lovely pleated new foliage of Lady’s  mantle (Alchemilla mollis), or the fresh mounds of green leaves on Geranium and Heuchera. The new foliage of Allium and goatsbeard (Aruncus dioicus) foretell flowers in the weeks to come, and the new growth of daylilies (Hemerocallis) holds out the promise of high summer.

new spring growth

Best of all, though, spring clean-up reveals a hillside of flowering crocuses.

side slope crocus blooms

Finally Spring: GBBD, April 2019

April 18, 2019

March crocus PickwickI’m even later than I normally am for Garden Bloggers’ Bloom Day. Blooms are sparse in my mid-April garden, but spring has finally arrived. In Maine, it is usually April that comes in like a lion and goes out like a lamb. As fellow Mainer Gary commented on an earlier blog post, April in Maine is “like a battle of two seasons.” In the first half of April, it can seem as though winter is winning that battle, and I can begin to wonder if spring will ever come. By the second half of April, though, spring is ascendant.

This year, the first ten days of April brought a series of small snow storms that re-covered any garden areas that were free of snow. This is what it looked like on April 10.

april 10 snow

Less than a week later, however, temperatures had gotten up into the sixties for the first time in more than six months, and the snow was melting fast.

melting snow 2019

fading foundation crocusIndeed, the early-blooming clumps of Crocus vernus ‘Pickwick’ by the south foundation of my house (photographed at the top of this post when they were at their peak) are already fading. Happily, though, many more crocuses are yet to bloom.

crocus budscrocuses emerging

spring cleanup back gardenIn the back garden, I have begun spring clean-up, revealing hyacinth buds about to open and new foliage of Lady’s mantle (Alchemilla mollis).

hyacinth buds 2019 new alchemilla foliage

Garden Bloggers’ Bloom Day is hosted on the 15th of each month by Carol at May Dreams Gardens. Visit her blog to see what’s happening in gardens where spring has truly sprung.