By Victoria Wallace and Alyssa Siegel-Miles, UConn Extension

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Regular scouting of lawn and landscape areas for pests, including weeds, is a critical component of a sound Integrated Pest Management (IPM) approach. When plants in the landscape are stressed due to environmental conditions that provide less than optimal growing conditions, weeds can easily establish and compete for nutrients, sunlight, water, and space. The key to managing weeds in the landscape is preventing conditions that allow for weed invasion and implementing proper cultural practices.

The simplest definition of a weed is “a plant growing where it is not wanted.” Weeds can be found in any location; however, many favor and populate an area in greater concentration in specific soil conditions. Prevalent in many landscapes, these weeds are referred to as “indicator weeds,” as they provide clues relating to the health of the soil, nutrients present, growing conditions, and the potential health of the landscape plants. Recognizing the conditions in which they usually grow, and looking within those site parameters to select plant material appropriate to those particular site conditions, is part of a long-term successful strategy that can displace weeds with more favorable plants. Soil conditions that directly affect plant growth include acidity, excess moisture, drought, compaction, low light, and low fertility.

 

To reduce weed infestations, one of two strategies can generally be employed:

1. Ensure that plants in each landscape location are suitable for the existing conditions.

• Desired plants growing in unsuitable growing conditions will lead to poor health and open areas. Weeds will germinate and fill in any bare soil.
• The more ground that is covered by appropriate, desirable plants, or mulch, the fewer spaces weeds will have to infiltrate and establish. Encourage the health of the desired landscape plants to discourage weed populations.
• Challenging areas, such as those that stay wet for the majority of the year, can become a valuable asset when embraced and incorporated into the overall garden design.

 

 

2. The soil can be amended to accommodate desired plants that prefer differing conditions, which will also discourage the current weeds from growing.

• For example, if weeds present in an area indicate that the soil to be planted is infertile or of poor quality, and plants that require higher fertility are desired (e.g., tomatoes, annual flowering plants, roses), the soil can be amended with compost (once the quantity needed is confirmed with a soil test). As the soil fertility is improved over time, it will support the desired plants’ needs and discourage the survival of those weeds that prefer or require a more infertile soil.

The success of any weed management strategy should depend first on the identification and biology of the weed, then coordinating the proper identification with the correct timing and method of establishment.  Understanding the life cycle of the weeds present in the landscape helps to determine the most effective control strategy to discourage their growth.

 

 

 

Low Fertility Soils 

To reduce weeds in an area of low fertility, test the soil to obtain an accurate indication of which nutrients are deficient. If desired plants are those that require a high or more neutral fertility program, amend the soil as needed with compost, cover crops, or organic fertilizers, such as fish meal or bonemeal, to raise the pH and add nutrients.

 

Alternately, plant the area with desirable species that are recognized to thrive with few nutrients.

 

These include:

Ornamental Perennials:

blanket flower (Gaillardia x grandiflora)

coreopsis (Coreopsis spp.)

globe thistle (Echinops ritro)

goldenrod, sweet (Solidago odora)

goldenrod, gray (Solidago nemoralis)

lamb’s ears (Stachys byzantina)

ornamental sage (Salvia spp.)

rattlesnake master (Eryngium yuccifolium)

silvermound (Artemisia schmidtiana)

yarrow (Achillea spp.)

 

Ornamental Shrubs:

American filbert (Corylus americana)

bayberry (Morella pensylvanica)

beaked filbert (Corylus cornuta)

Northern bush honeysuckle (Diervilla lonicera)

fragrant sumac (Rhus aromatica ‘Gro-Low’)

ninebark (Physocarpus opulifolius)

shrubby potentilla (Potentilla fruticosa)

 

 

Solution plants:

Acidic Soils 

Acidic (sour) soils have a pH below 6 (a pH of 7 is neutral, above 7 is alkaline). Most garden plants grow best when the soil pH is between 6.0 and 7.2. At a neutral pH, some of the most important nutrients are most readily available to plants. If the soil pH is too high or low, phosphorus (responsible for helping a plant produce blooms and fruit), and several other nutrients become insoluble and unavailable to plants. Some other nutrients, such as iron, copper, and zinc, are more readily available when the soil is more acidic. Plants that thrive in acidic soils require more of these nutrients. Plants that thrive with high quantities of nitrogen, phosphorus, and calcium, which are more available at a neutral pH, include many introduced, non-native ornamentals and most vegetable plants.

To reduce weed populations in acidic soils, select and plant species, including many natives, that naturally prefer and thrive in an acidic soil. Plantings thick with acid-loving plants will keep weeds to a minimum. Acid-loving plants include:

azalea hydrangea

bleeding heart Japanese pieris

blueberry magnolia

dogwood pine

elderberry rhododendron

ferns (all types) rhubarb

fothergilla viburnum

Alternately, if plants that are challenged to tolerate and persist in acidic soils are desired, such as many vegetable plants and some ornamentals (e.g., lilacs, clematis), amend the soil to raise the pH by incorporating the appropriate amount of dolomitic limestone and compost into the soil (based on soil test results).

 

Acid-loving weeds:

USE THESE WEEDS TO IDENTIFY ACIDIC SOILS:

Common Name (Botanical Name)	Life Cycle
Bentgrass (Agrostis spp.)	Perennial
Broadleaf plantain (Plantago major)*	Perennial
Silver cinquefoil (Potentilla argentea)*	Perennial
Hawkweed (Hieracium spp.)	Perennial
Knapweed (Centaurea spp.)	Summer Annual
Lady's-thumb smartweed (Polygonum persicaria)*	Summer Annual
Prostrate knotweed (Polygonum aviculare)*	Summer Annual
Red (sheep) sorrel (Rumex acetosella)*	Perennial
Sowthistle (Sonchus spp.)	Perennial

 

Wet Soils 

Wet areas in the landscape are a valuable asset when they are embraced and incorporated into the overall garden design. Efforts to change the soil conditions are likely to be costly and labor intensive, but often are not successful. Design wet areas to serve as “natural” rain gardens. Planted with desirable species that thrive with “wet feet,” rain gardens allow rainwater runoff to infiltrate and be absorbed into the soil. They clean, slow the rate of infiltration, and reduce the volume of stormwater. Specific, appropriate plants, which can withstand the extremes of moisture and concentrations of nutrients (particularly nitrogen and phosphorus) often found in stormwater runoff, are utilized.

Plants that thrive in a rain garden include:

  blue flag iris (Iris versicolor)

  cardinal flower (Lobelia cardinalis)

  curly willow (Salix matsudana)

  dogwood (Swida spp., previously Cornus spp.)

  joepye weed (Eutrochium purpureum)

  pussy willow (Salix discolor)

  river birch (Betula nigra)

  soft rush (Juncus effusus)

  swamp milkweed (Asclepias incarnata)

  white turtlehead (Chelone glabra)

For more information, download the Rain Garden app developed by UConn’s NEMO Program.

 

USE THESE WEEDS TO IDENTIFY WET SOILS:

Common Name (Botanical Name)	Life Cycle
Annual bluegrass (Poa annua)*	Winter Annual
Common chickweed (Stellaria media)*	Winter Annual
Curly dock (Rumex crispus)	Perennial
Horsetail (Equisetum arvense)	Perennial
Lady’s-thumb smartweed (Polygonum persicaria)*	Summer Annual
Mouse-ear chickweed (Cerastium virgatum)*	Perennial
Pennsylvania smartweed (Polygonum pensylvanicum)	Summer Annual
Yellow nutsedge (Cyperus esculentus)	Perennial

*Found in multiple categories.

Drought-Prone Soils 

The soil’s ability to retain water dictates how, and at what pace, water moves through the soil. A drought-prone soil is a soil in which water moves quickly though the soil profile. The composition and texture of the soil (e.g., sand, silt, or clay) influences the soil’s ability to hold water. Soils high in clay, silt, and organic matter hold water more readily than others. Soils that are sandy or low in organic matter are more prone to drought, drying out quickly (within a few days) when evaporation and transpiration rates are high due to heat, dry air, and wind.

• A soil in good health has a higher capacity to retain water for optimal lengths of time for healthy plant growth. Soil management practices that improve soil quality and enable plants to tolerate periods of drought include:
• Add organic matter to the soil, such as leaf mulch and compost. Among other benefits, organic material will encourage beneficial microbial activity, which improves rainwater infiltration and root development. The amount of organic matter applied should be determined based on soil test results, to ensure that nutrients, especially phosphorus, are not overloaded.
• Maintain soil pH at the appropriate level for the plants being grown.
• When plants are grown in soil with inappropriate pH levels, root growth is restricted. Plants with a smaller root system are unable to access available water that is lower in the soil profile
• Control erosion by ensuring that soil is covered by mulch or plants at all times. For example, grow cover crops or mulch bare soil in vegetable gardens overwinter. Under tree canopies, reduce bare soil with appropriate groundcover plants, such as white wood aster (Eurybia divaricata).
• Potassium nutrition is closely linked to soil’s ability to retain water. Optimum levels of potassium supplied in the soil improve plants’ ability to withstand drought stress (Heckman).
• Alleviate soil compaction, which negatively impacts soil quality and limits root growth.
• Avoid heavy foot or vehicle traffic on areas where plant growth is desired.

 

Drought-loving weeds:

USE THESE WEEDS TO IDENTIFY DROUGHT-PRONE SOILS:

Common Name (Botanical Name)	Life Cycle
Black medic (Medicago lupulina)	Summer Annual
Crabgrass (Digitaria spp.)	Summer Annual
Goosegrass (Eleusine indica)*	Summer Annual
Plantain (Plantago spp.)*	Perennial
Silver cinquefoil (Potentilla argentea)*	Perennial
Prostrate knotweed (Polygonum aviculare)*	Summer Annual
Red (sheep) sorrel (Rumex acetosella)*	Perennial
Spotted spurge (Euphorbia maculata)*	Summer Annual
White clover (Trifolium repens)*	Perennial
Virginia pepperweed (Lepidium virginicum)	Perennial
Woodsorrel (Oxalis stricta)	Perennial

*Found in multiple categories.

USE THESE WEEDS TO IDENTIFY COMPACTED SOILS:

Common Name (Botanical Name)	Life Cycle
Annual bluegrass (Poa annua)*	Winter Annual
Bindweed (Convolvulus arvensis)*	Perennial
Broadleaf plantain (Plantago major)*	Perennial
Common chickweed (Stellaria media)*	Winter Annual
Chicory (Cichorium intybus)	Perennial
Corn speedwell (Veronica arvensis)	Winter Annual
Dandelion (Taraxacum officinale)	Perennial
Goosegrass (Eleusine indica)*	Summer Annual
Mouse-ear chickweed (Cerastium virgatum)*	Perennial
Path rush (Juncus tenuis)	Perennial
Prostrate knotweed (Polygonum aviculare)*	Summer Annual
Spotted spurge (Euphorbia maculata)*	Summer Annual
Wild garlic (Allium vineale)	Perennial

*Found in multiple categories.