University of Vermont Extension
Department of Plant and Soil Science
Dr. Leonard Perry, Extension
University of Vermont
We're not talking here about
gardeners that are bullies, rather plants that many refer to as thugs
bullies. Knowing which to avoid, or
proper placement, can prevent the gardener turning into a bully on
unwanted plants and perhaps losing the battle.
The problem with our anthropomorphic
characterization of these aggressive plants is that it really isn't
fault, but ours. Plants aren't
inherently evil, they didn't grow up trained or conditioned to be
bullies. They are just responding to their genetic
makeup and environment.
All plants have a right place or
habitat, the problem is when WE put them in the wrong place or they
respond as WE would like where they are planted. So the key is to
realize what we want out of
a plant, then choosing the right plant, or if we have a plant to know
"behavior" or growth needs and to place it properly. An example is
the aggressive root spreaders which, when put in a garden, can overtake
plants and become the garden. However,
place these same plants in a poor site, or between a rock and a hard
literally (such as surrounded by pavement) and they will stay in place.
Plant thugs can be placed into at
least 4 groups, according to consultant Kerry Mendez (www.pyours.com).
If not thugs against other plants, they may
be against our time and desires, so I like to refer to them as "plants
with issues". These groups include
those that reseed, those that spread by roots, those that take lots of
time, and those that are short-lived so need frequent replanting.
Reseeding can be good if you want
more of a cottage garden look (just weed out the unwanted seedlings),
naturalistic garden. (Or if you end up with such plants and their
these themes with those viewing your garden.)
Yet if you want a neat and tidy garden, reseeding can be an issue.
Cultural controls begin with removing flowers once done, before they go
seed, but this can be time-consuming. A
heavy layer of mulch, perhaps with a ground fabric beneath in the case
annual flowers, prevents seeds from reaching the soil. Of course
can use good old-fashioned
weeding if the time.
If a plant reseeds into a wild area,
displacing desirable native plants, it is said to be invasive.
happens with herbaceous plants such as
purple loosestrife, and several woody ornamentals. Keep in mind, too,
depending on climate and soil, some plants may reseed in one area and
not another. A good example of both these points is the
Miscanthus grasses, which go to seed in warm climates (such as below
York city area) but not in colder climates where they are not invasive.
Some potential perennial reseeders
include the 'Golden Jubilee' hyssop, some rudbeckias, tall garden
bluets, blue cardinal flower, spurge, yarrow species (not many
hybrids), and mallows. Some common
annuals that may reseed are amaranths, the balsam impatiens or
(touching the seed pods makes the seeds explode out), cosmos, cleome,
larkspurs, old-fashioned petunias (not the hybrids you usually find),
(in some areas), the tall vervain, flowering tobacco, some black-eyed
and violas. Foxgloves are biennials that often reseed.
In another group are those that
spread by roots. My definitions are if
they spread and can be controlled by a yearly hoeing, they are
spreaders. If they need several yearly hoe attacks to
keep in bounds they are aggressive. If
once you plant it you have it forever, I call this an invasive root
spreader. Examples of the latter include
goutweed, Japanese knotweed or bamboo, and silver
Other perennials most consider too
root invasive to plant in gardens are the yellow and gooseneck
blue lyme grass, mints, spotted bellflower, ladybells, Chameleon plant,
Japanese anemone, plume poppy, snow-in-summer, perennial periwinkle
warm climates), spotted deadnettle (can make a nice groundcover in
bugle, artemisias and some evening primroses.
A red flag word to watch for in catalogs and plant descriptions is
"vigorous". Watch the cultivar
descriptions as some cultivars may not be spreaders. While the
loosestrife is aggressive,
'Alexander' with its variegated leaves is a clump former. While most
spread, 'Silver Mound' is just that and a non-spreader.
As with the reseeders, some root
spreaders are less a problem in some areas, as in poor soils with low
fertility. Placement is a key point with
these. I have a plume poppy for
instance, which placed between a mown path and a brick wall is no
the birds love it for perching near the adjacent feeders. (The
leaves look great too against the
red brick wall.) Another key point is if
weeding them out, don't throw just anywhere.
Such plants can be thrown on top of a mature field, and end up taking
hold and becoming the field. Definitely
keep from waterways where the smallest root pieces can wash down
then take over.
One method many use to contain such
spreaders as mint and bee balm that you may want, is to plant them in
pots, then sink the pots in the ground.
Roots will reach the pot sides, then begin to circle. This can go
for a year or two before
plants die out, so if you want to save them you'll need to repot every
two. Beware of the holes through which
roots (such as of the mint) can escape their confines and colonize the
surrounding bed (as I learned the hard way).
The third group includes those that
take more time than we want to spend on them, such as
with frequent dividing, staking, and deadheading (pinching off) spent
flowers. The latter just may be
aesthetic, or it may relate to preventing self-sowing. Luckily,
new annuals are
"self-cleaning", dropping their flowers naturally and not needing to
be deadheaded as in the past. Instead of
cultivars that need staking, look for shorter versions. Or prune
late-season bloomers like asters,
false sunflower, even tall garden phlox, back about a third in early
summer to promote
branching and lower growth without staking.
Related in issue to the last group
are those perennials that are short-lived, requiring more time to
replant than we want or have to give.
Some in this group include delphiniums, cardinal flower, blanket
flowers, some pinks or dianthus, lupines, and columbines. As with
other groups there are exceptions,
both in plants and from climate and soil conditions.
Of course if a plant starts getting
out of bounds, chemical herbicides can be used.
There are synthetic and organic ones that just burn back the leaves--
good for annuals. If you're trying to
control the roots too, you may need a systemic herbicide-- one such as
glyphosate that is translocated through the plant system. If
these "big guns", be sure
and follow all label directions, keeping in mind they are usually
non-selective. This means they can kill
desired plants just as well as the target ones if not applied properly.
invasive root spreaders, several applications over several years may be
to keep them under control.
If such spreaders have taken over
your garden, you may want to consider either removing the desired
giving in to the thugs (easy solution, as I've done in some beds), or
in a backhoe to remove and replace all the soil (extreme solution).