Healthy lawns offer strongest defense against weeds, says K-State horticulture expert

 

Proper mowing, watering and soil care can help homeowners prevent weed invasions

 

At a glance: Proper maintenance and a healthy lawn may be the best defense homeowners have against invasive weeds, said Kansas State University horticulture expert Matt McKernan.

More information: Matt McKernan, hortsupport@ksu.edu

Related: K-State Horticulture Newsletter

A healthy lawn is the best defense against weeds, says K-State horticulture expert Matt McKernan.

June 5, 2026

By Pat Melgares, K-State Extension news service

MANHATTAN, Kan. — A healthy lawn may be the best defense homeowners have against invasive weeds, said Kansas State University horticulture expert Matt McKernan, adding that proper maintenance can prevent many common weed problems before they begin.

“Weeds invading a home lawn can feel like an ongoing battle,” McKernan said. “Instead of constantly applying chemical treatments, homeowners should focus on growing strong, vigorous turfgrass that naturally crowds out weeds.”

McKernan said healthy grass competes with weeds for sunlight, water and nutrients, making it harder for unwanted plants to take hold. He noted that many weed problems stem from common lawn care mistakes that weaken turfgrass and create opportunities for weeds to spread.

One of the most common problems is mowing grass too short. McKernan said scalping the lawn weakens turfgrass and allows more sunlight to reach weed seeds, encouraging germination. He recommends mowing at the proper height for the grass species, keeping mower blades sharp and avoiding mowing when grass is wet.

Watering practices also play a significant role in lawn health. Frequent, shallow watering encourages shallow root systems and can increase weed pressure, McKernan said.

Instead, homeowners should water deeply and less often to promote stronger roots and improve drought tolerance. During spring, irrigation should only occur when necessary.

Other factors that may lead to an unhealthy lawn include:

• Improper fertilizing.Fertilizing too much or too little or at the wrong time may benefit weeds more than grass. Only fertilize during the recommended months, only apply what is needed, and conduct a soil test to better understand fertilizer needs.
  
  
• Compacted soil.Soil compaction is a hidden stress on the turfgrass root system. The grass is unable to compete effectively with weeds. Core aerate lawns at least once per year to reduce compaction.
  
  
• Excessive wear.Turf areas used for recreation, sports and pets are subject to wear and compaction. Core aerate to reduce compaction in these areas, and temporarily fence off areas when establishing new grass seed.
  
  
• Wrong kind of grass.The wrong variety for the location will gradually decline and be invaded by weeds. Always check the grass seed label before purchasing to evaluate the types of grass seeds included in the bag. Purchase only recommended types of turf, avoiding cheap fillers.
  
  
• Environmental stress.Weeds often take over a lawn after it has been weakened and thinned from weather-related stress. Water appropriately during times of drought and avoid overwatering in the spring and fall. Evaluate irrigation water quality and soil nutrient levels by testing.
  
  
• Thatch. Excessive thatch causes shallow-rooted grass, limits water infiltration and contributes to insect and disease problems. Regularly monitor thatch accumulation and remove excessive thatch when necessary.

McKernan said a proactive approach focused on lawn health is more effective and sustainable than relying solely on herbicides.

“A dense, healthy lawn is the first line of defense against weeds,” he said.

McKernan and his colleagues in K-State’s Department of Horticulture and Natural Resources produce a weekly Horticulture Newsletter with tips for maintaining home landscapes and gardens.

Interested persons can subscribe to the newsletter, as well as send their garden and yard-related questions to hortsupport@ksu.edu, or contact your local K-State Extension office.

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K‑State Extension is a short name for the Kansas State University Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the wellbeing of Kansans. Supported by county, state, federal and private funds, the program has county extension offices statewide. Its headquarters is on the K‑State campus in Manhattan. For more information, visit www.ksre.ksu.edu. K-State Extension is an equal opportunity provider and employer.