head off invasive weed, garlic mustard, and divide perennials
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[APRIL 18, 2006]
A new weed problem has reared its ugly head
in the Logan County area. Garlic mustard is making its presence
known in many wooded, or formerly wooded, areas. No, garlic mustard
is not exactly new, but it is expanding its range at a very speedy
Garlic mustard is considered an invasive species, and some
states have declared it a noxious weed. Illinois hasn't declared
it such, at least not yet. The problem with garlic mustard is
how quickly it spreads. It spreads so quickly it tends to choke
out much of the desirable undergrowth in timber areas.
mustard is a cool-season biennial herb with stalked, triangular
to heart-shaped, coarsely toothed leaves that give off an odor
of garlic when crushed. First-year plants appear as a rosette of
green leaves close to the ground. Rosettes remain green through
the winter and develop into mature flowering plants the
following spring. Flowering plants of garlic mustard reach from
2 to 3 1/2 feet in height and produce buttonlike clusters of
small white flowers, each with four petals in the shape of a
Control of garlic mustard is somewhat difficult. Seeds can
remain viable for at least five years in the soil. Small amounts
can be pulled up (including the roots). Garlic mustard can
regrow from root material. With herbicides, glyphosate (Roundup)
is the most often recommended. Remember, glyphosate kills
broadleaves and grasses it gets on. There has been some success
with 2,4-D LV400 where there aren't concerns with other
understory plants. Very large patches have been controlled with
fire, but that completely destroys the understory of timbers.
Remember to monitor areas for at least five years due to the
seed dormancy period.
Some action at this early time may help prevent larger
problems down the road. It is much easier to control small
patches than large ones.
A common maintenance chore in a perennial garden is that of
dividing. There is no set rule as to when to divide perennials.
Some may need division every three to five years, some eight to
10 years, and some would rather you not bother them at all.
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Perennials will send signals to let you know that they would like
to be divided. The signals to watch out for include these: flowering
reduced, with the flowers getting smaller; growth in the center of
the plant dies out, leaving a hole with all the growth around the
edges; plant loses vigor; plant starts to flop or open up, needing
staking; or it just may have outgrown its bounds. These are the
signs to look for and not a date on the calendar.
If division is indicated, spring is the preferred time to divide.
Some fleshy-rooted perennials, such as poppy, peony and iris, are
best divided in the late summer to very early fall.
Division is usually started when growth resumes in the spring.
The process starts by digging around the plant and then lifting the
entire clump out of the ground. Then, using a spade or sharp knife,
cut the clump up so that each portion is the size of a quart- or
Discard the old, dead center and trim off any damaged roots. The
divisions should be kept moist and shaded while you prepare the new
planting site. After replanting, water well and protect the
divisions from drying out.
Division is no more complicated than this. Some perennials may be
more difficult to divide than others because of their very tenacious
root system. Division has as its primary goal the rejuvenation of
the perennial planting so it can continue to perform the way it was
intended. Many home gardeners have found that the process of
division is more traumatic to them, the gardener, than it is to the
Fulton, unit leader,
University of Illinois Extension,
Logan County Unit]