Weeds
can be found in a wide range of locations. Some weedy plants are
more likely to be found in specific environmental conditions. These
plants are sometimes called indicator species because their presence
provides clues about the existing environmental conditions, such as
soil compaction, acidic soil, excess moisture, dry soils, low light,
and low fertility. While indicator plants can grow in other
conditions, their presence might be a sign for you to investigate
soil and environmental conditions.
There are two main strategies to reduce weed infestations. The first
is ensuring the right plant is in the right conditions to thrive.
The second is to amend the soil or conditions to create a less
favorable environment for weed growth.
It is essential to identify weeds so they can be correctly
controlled. Once the weed is identified, some research will provide
information on its life cycle to help determine the best methods to
discourage growth.
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Low Fertility
Plants such as the common mullein (Verbascum thapsus), plantain (Plantago
spp.), and white clover (Trifolium repens) can be indicators of low
fertility. A soil test is an excellent way to verify this.
Low-fertility soil can be modified by adding organic matter through
cover crops, compost, or organic fertilizers such as bone or fish
meal.
Another option is to select plants that thrive in low fertility
conditions to out-compete the weeds.
Perennials
Coreopsis (Coreopsis spp.)
Globe thistle (Echinops ritro)
Goldenrod, sweet (Solidago odora)
Ornamental sage (Salvia spp.)
Blanket flower (Gaillardia x grandiflora)
Rattlesnake master (Eryngium yuccifolium)
Yarrow (Achillea spp.)
Shrubs
American filbert (Corylus americana)
Fragrant sumac (Rhus aromatica Gro-Low)
Ninebark (Physocarpus opulifolius)
Wet Soils
Certain weed species indicate excess moisture. Species such as
annual bluegrass (Poa annua), common chickweed (Stellaria media),
Pennsylvania smartweed (Polygonum pensylvanicum), and yellow
nutsedge (Cyperus esculentus) hint at too much moisture in that
area.
These areas can be a good spot to add native water-loving plants for
a natural rain garden. Rain gardens give water a place to infiltrate
the soil, which also cleans the water and reduces runoff. [to top of second
column] |
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These plants thrive in wet conditions:
Blue flag iris (Iris versicolor)
Cardinal flower (Lobelia cardinalis)
Dogwood (Swida spp.)
Joe Pye weed (Eutrochium purpureum)
River birch (Betula nigra)
Pussy willow (Salix discolor)
Swamp milkweed (Asclepias incarnata)
White turtlehead (Chelone glabra)
Soils that dry quickly
Soils prone to drought do not retain as much water as other soils,
creating a favorable environment for weedy species such as crabgrass
(Digitaria spp.), plantain (Plantago spp.), prostrate knotweed (Polygonum
aviculare), and woodsorrel (Oxalis stricta).
Improve soil health using soil-friendly garden practices and add
organic matter to help the soil better hold onto water. Control
erosion by leaving plants or mulch on the soil. Use soil tests to
monitor soil fertility, paying close attention to potassium levels,
which can be low in drought-prone soils.
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Compacted Soils
Bindweed (Convolvulus arvensis), broadleaf plantain (Plantago
major), chicory (Cichorium intybus), dandelion (Taraxacum officinale),
and prostrate knotweed (Polygonum aviculare) can be indicators of
soil compaction. Reduce compaction by adding organic matter,
redirecting foot traffic, or core aerating the soil to make a less
favorable environment for these species.
Plants can adapt to a range of conditions, and it is important to
note that some species can thrive in more than one environment, so
using weeds as indicators of conditions is just one way to read the
hints a garden is giving. Use the clues to dig deeper and create a
less favorable environment for weedy invaders. This approach is not
foolproof, but it is a place to start to reduce weed infestations.
Nicole Flowers-Kimmerle is an Illinois Extension horticulture
educator for Fulton, Mason, Peoria, and Tazewell counties. Gardeners
Corner is a quarterly newsletter from gardening experts around the
state. Each issue highlights best practices that will make your
houseplants, landscape, or garden shine in any season. Join the
Gardeners Corner email list at go.illinois.edu/GCsubscribe for
direct access to timely tips.
[Nancy Kreith, Extension Educator,
Horticulture, University of Illinois Extension ] |