One disadvantage of some perennials is that they are invasive--they
spread where you don't want them and are difficult to control and
keep in gardens. They may spread by roots, as in the case of mints,
or by seeds, as in the case of Purple Loosestrife. Those spreading
by roots can be useful if in a confined situation, or used in rough
areas, such as slopes, to control erosion. In perennial beds, the
root-spreaders can kill less vigorous species and take over most
the bed. Those spreading by seeds may be useful--as with many field
wildflowers--yet some, such as Purple Loosestrife, colonize wet
areas, eventually destroying them and the wetland wildlife habitats.
Purple Loosestrife and other similar invasive perennials are banned
from sale in many states for this reason.
invasive nature of perennials is relative. Many on the following
list may not even be hardy in certain areas, therefore acting neither
as perennials nor problems in these areas. Or they may be hardy,
though not vigorous or a problem, in many areas. Others, especially
the root-spreaders, may be less or not invasive, depending on factors
such as culture and soil types. Those invading by seed may not be
a problem in northern areas if the short growing season keeps them
from going to seed (such as some silver grasses).
term "invasive" is itself relative. To some, this means any plant
spreading at all. To others, an invasive perennial is one that not
only spreads but is also quite vigorous and difficult to control.
Those that spread but can be controlled by yearly cultivating or
dividing are termed either "spreading" or "aggressive," depending
on how fast they spread.
than cultivating, dividing and weeding out seedlings, root-spreading
perennials may be controlled by planting them in containers either
in or on the ground. If in the ground, make sure roots do not exit
the drain holes or go over the top. If you want to keep these perennials
from year to year, they may need to be divided and repotted annually
to keep them from dying out. Systemic herbicides may also be used
to control root-spreading perennials; several applications may be
necessary to provide control. Herbicides that act by merely burning
back the foliage are not very effective with vigorous perennials,
which merely resprout from the roots. If using any herbicide, read
and follow all label directions.
The following list is only a beginning of some of the more common
perennials listed as invasive by some, in some areas of the world.
Others, especially those that "self sow" once they go to seed, may
be in this group as well. Some species or cultivars of a perennial
may be invasive, and others not--the listing of a genus below does
not mean that all of its members are invasive. This list should
be used only as a "red flag" to check closer into a particular plant
or genus of perennials before planting.
Anemone x hybrida
Artemisia ludoviciana and cv's
Aster (certain species e.g., ericoides)
Euphorbia amygdaloides var. robbiae
Filipendula rubra 'Venusta'
Persicaria virginiana 'Painter's Palette'
Phalaris arundinaceae var. picta
Verbena cultivars (e.g.,
Creeping St. John's Wort
from Leonard P. Perry, University of Vermont Extension, 2000