Indicator Weeds Provide Insight into Growing a Better Lawn

“Right plant. Right place.” It is an adage that gardeners turn to when choosing plants for the landscape. If plants are matched to their preferred conditions, such as light, moisture, soil pH, and nutrients, their success is better assured. This adage works for those plants we don’t choose as well—weeds. Weeds are opportunists. If given the conditions that they tolerate, they will take the opportunity to germinate and spread. Weeds can thrive under fairly favorable conditions and under pretty adverse conditions, too. Most turfgrass species, blends, and mixes that are successful in Pennsylvania are cool-season varieties that prefer a sunny site with nutrient-rich soil that drains well and has a pH between 6.0 and 7.2. Starting with the right soil conditions and then utilizing the correct cultural practices can increase the vigor of turfgrass and create a density that won’t allow weed seeds the sunlight or nutrients to get established. Understanding the conditions under which different weeds flourish can dictate how to change those conditions in your lawn and suppress those weeds without relying continually on herbicides. Provide the conditions that your grass needs and weeds will not succeed.

Indicators of Improper Mowing

White clover (Trifolium repens) is a weed that indicates that the mowing height for turf is lower than desired. Mowing heights of at least 2 inches (3 inches is better for some species) will create a taller canopy of grass, decreasing the penetration of sunlight to the soil and the germination of the waiting bank of weed seeds. A tall canopy also leads to deeper roots, creating a turf that can more easily thrive when hot and dry conditions arise. Another important aspect of mowing is to have sharp blades. Sharp lawnmower blades make clean cuts, reducing the potential for diseases that may start in wounded grass tips and lead to weakened turf areas. Mow as often as the grass needs it. One rule is to not remove more than 1/3 of the leaf blade at any time. During rapid growth in the spring, lawns may need mowing more than once per week. During the heat of the summer, especially when dry, you may not need to mow more than once every two weeks. Using a mulching mower and leaving the clippings on the grass will basically deliver free fertilizer—reducing supplemental fertilization needs by as much as half.

Indicators of High Acidity and Low Fertility

Plantain (Plantago major), red sorrel (Rumex acetosella), crabgrass (Digitaria sanguinalis), and prostrate knotweed (Polygonum aviculare) are indicator weeds for acid soils. Submit a soil test to Penn State for your turfgrass areas and use the lab’s recommendations to adjust the pH of your lawn. Penn State labs will also make recommendations for fertilization. Follow their recommendations even though the prevalence of different weeds may have already led you to believe that the soil was infertile. Plantains, red sorrel, crabgrass, and white clover also indicate low-fertility soil. White clover indicates infertile soil that is wet. Yarrow (Achillea millefolium) indicates dry infertile soil.

Indicators of Excessive Fertility and Moisture

Follow the recommended schedules for annual fertilization and heed the recommended pounds of fertilizer for the turf area. More is not better and may just lead to weeds that prefer high-fertility soils. If the soil is too fertile, the lawn might become plagued by purslane (Portulaca oleracea), dandelion (Taraxacum officinale), lamb’s-quarters (Chenopodium album), henbit (Lamium amplexicaule), or yellow woodsorrel (Oxalis stricta). If the soil is both wet and too fertile, yellow woodsorrel, henbit, and curled dock (Rumex crispus) may be the weeds that rule it.

Indicators of Poor Drainage

A lawn plagued with mosses indicates that it is wet and drains poorly. Additional weeds may also indicate those conditions, such as common chickweed (Stellaria media), ground ivy (Glechoma hederacea), mouse-ear chickweed (Cerastium vulgatum), yellow nutsedge (Cyperus esculentus), and violets (Viola spp.).

Indicators of Compacted Soil

Compacted and heavy soils can be indicated by dandelion, chickweed, plantain, mouse-ear chickweed, and prostrate spurge. To improve drainage and reduce compaction, lawn aeration may be warranted. This process is best performed while the grass is actively growing in the spring or fall. A machine will remove the plugs of the existing soil. Overseeding after the aeration will help create a denser turf.

Indicators of Dry Soil

Black medic (Medicago lupulina), prostrate spurge, and red sorrel indicate dry soil. If rainfall isn’t sufficient, supplemental irrigation may be warranted. Remember to water thoroughly and deeply. Research shows that watering just as the grass begins to wilt and applying 4 to 6 inches of water is ideal. Alternatively, use a soil probe to monitor the level and depth of soil moisture. Roots follow moisture. Frequent shallow watering creates shallow root systems. Deep watering creates deep root systems that will be able to better withstand the next dry spell.

Indicators of Excessive Shade

Turfgrass generally prefers the sun. In shaded areas, the turf will thin, and you may see indicator weeds like common chickweed, ground ivy, and mouse-ear chickweed. Limbing up the shrubs or trees may reduce the shade. Alternatively, choose another groundcover to grow in that area or reseed with a variety of turfgrass that will tolerate some shade.

Removing Weeds in Turfgrass

To reduce weed populations, mow before they set seed. Hand pull or hoe weed patches, trying to remove as much root as possible. If herbicide use is warranted, always follow the instructions on the label and remember that more is not better.

The weeds in your grass can indicate that their preferred conditions are being met instead of those that the turfgrass prefers. Cultural methods—mowing, watering, amending, and fertilizing—applied correctly to grass can go a long way toward remedying the conditions that make it easy for weeds to infiltrate your lawn.

Valuing Diversity in Lawns

This article has addressed the creation of a healthy lawn that is relatively weed free without the use of herbicides. Many gardeners desire plants like white clover and violets in their lawns to support pollinators and other wildlife. Learning to value a diversity of plants within an expanse of grass is not only beneficial to the environment, but it is also a lot less work, time, expense, and worry for the gardener.