Understanding Weeds

Weeds may sometimes seem to have extraordinary capabilities compared to other plants, but this is their “competitive edge”. Weed seeds may have arrived in your neighbor’s lawn via a multitude of pathways: wind, water, ballistically, in animal scat, or they were already present in the soil’s seed bank. These dispersal methods were genetically favored over time and increased weedy plant’s overall competitive fitness. Another favored characteristic of weeds is their ability to germinate in the most adverse conditions; water, light, and nutrients may be limited, but the plant will persist. Once the weed seed has found its new home and has begun the germination process, it will grow vigorously until it reaches maturity. Some weeds have the unique trait of self-compatibility, meaning that these plants have both male and female reproductive structures. This is an emergency response mechanism in case the rest of the population dies out, this living plant can repopulate by itself. Mature plants will disperse hundreds of small seeds that house themselves in the soil. The accumulation of weed seeds in the soil is called the “soil seed bank”. These seeds can be eaten by soil-dwelling organisms, decay, germinate and unsuccessfully establish, or will germinate and successfully emerge. While you may have a good track record of keeping your lawn clean, unlike your neighbor, the weed seeds are still present within the soil waiting for the opportunity to establish.  

What is your neighbor looking to achieve? Most likely a uniform, green, pest free, and overall healthy lawn. For plants to live, they carry out fundamental processes requiring sunlight, water, and nutrients. Turfgrass managers supplement stands with irrigation, fertilization, and mowing. All three of these cultural techniques feed the turf, allowing it to grow vigorously. As soon as one of these cultural management techniques is neglected, such as mowing, you will see an over-grown lot like the other neighbor’s lawn a few doors down. Unfortunately, weeds will always be an uphill battle for turfgrass managers due to the ample amount of irrigation and fertilization these stands receive.

You can see that your neighbor has weeds in their lawn, but what specific weeds are they combating? It is critical to identify what weeds are at play because some weeds only respond to certain herbicides, while others may have no effect at all. Additionally, if your neighbor researches the weed’s characteristics, they can determine the best time of year to manage it and how it repopulates.

The first step in turfgrass weed identification is to determine its morphology: is the weed a grass or a broadleaf?

• Grassy weeds:
  • Monocot: One cotyledon coming out of the seed upon germination.
  • Parallel vein structure on the leaf.
  • Fibrous roots
  • Examples: Annual bluegrass (pictured below), sedges, crabgrass

• Broadleaf weeds:
  • Dicot: Two cotyledons coming out of the seed upon germination.
  • Netted or webbed vein structure on leaf.
  • Taproots
  • Examples: Dandelion, clover (pictured below), chickweed

Another way to identify weeds are by their lifecycle. Weeds can be characterized into three lifecycles: annual, biennial, and perennial.

• Annual: One growing season
  • Summer annual: Emerge in spring, die in the fall
  • Winter annual: Emerge in the fall, die in the spring
  • These rapidly deplete surrounding nutrients compared to other weeds and should be managed immediately.
  • Examples: Crabgrass, chickweed, common mallow (pictured below)

• Biennial: Two growing seasons
  • First year of growth, vegetative structure is formed
  • Second year of growth, reproductive structures are formed
  • Typically rosette-shaped
  • Examples, Common mullein, thistles (pictured below), poison hemlock

• Perennial: Two or more growing seasons
  • Can reproduce vegetatively and via seed
  • Creates a taproot for long-term nutrient storage
  • Examples, Buckhorn Plantain (pictured below), dandelion, Queen Anne’s lace

A multitude of university extension programs, online identification guides, and phone applications exist to help you and your neighbor figure out what is causing a nuisance on their lawn. These tools will ask if you know the weed’s lifecycle or morphology, in addition to that, they will ask if you can spot some other defining features such as where you found it, how it grows, hairs or spines present, or flower characteristics. Once the weed is correctly identified, some light internet research will provide you a laundry list of management methods. Generally, you will find that results simmer down into weed prevention, control, eradication, and management.