Everything You Need To Know About Grassy Weeds

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Grassy weeds, a common sight in many Arizona landscapes, are more than just an aesthetic nuisance. These pesky intruders compete with desirable plants for resources and can negatively affect the health of your garden or lawn if left unchecked. Understanding the characteristics of grassy weeds is the first step toward effective weed management. This guide aims to equip you with the knowledge to identify and control grassy weeds in Arizona.

What Are Grassy Weeds?

Grassy weeds are weeds that appear to look like grass. They are typically plants that are part of the part of the family called Poaceae, which includes common grass species such as Bermudagrass and St. Augustinegrass. In other words, grassy weeds are the same as any other grass you can find, including the grass that makes up your lawn. The difference between weeds and healthy grass is a matter of where and how they are growing.

For example, Bermudagrass is used as turfgrass in warm climates like ours, but it could be considered a weed if it found its way into a cool-season lawn in northern regions of the country. Grasses that grow in areas they are not acclimated to will behave differently (aggressive growth, more nutritional needs, etc.), which will disrupt the normal growth cycle of the existing grass in a lawn. Other grassy weeds can pop up anywhere in the world in undesirable soil conditions, making proper lawn care that much more important if you want to keep these unsightly grassy weeds out of your yard. Below are some of the most common grassy weeds found in Arizona:

  • Barnyardgrass
  • Annual Bluegrass
  • Nutsedge
  • Johnsongrass
  • Perennial Ryegrass
  • Wild Oat
  • Crabgrass
  • Foxtail

How To Identify Grassy Weeds

Grassy weeds pose a significant challenge when it comes to identification, as their appearance closely matches that of desirable lawn grasses. The subtle differences in texture, color, or growth patterns can be imperceptible to untrained eyes, making it hard to distinguish between the weed and the grass. The growth habits of grassy weeds may vary depending on the climate, soil conditions, and the presence of other vegetation, adding another layer of complexity to proper identification. After all, most grassy weeds are just other types of grass that belong to the same family as your lawn, so it takes a keen eye to spot the difference!

Despite these difficulties, there are a few strategies that can help the identification process. You can observe the growth pattern of the suspected weed. Grassy weeds may exhibit an unusual growth pattern, such as spreading rapidly across the lawn or appearing in bunches, which distinguishes them from common lawn grass. Homeowners can also look for variations in color and texture. Grassy weeds often have a different hue or feel compared to the rest of the lawn. Below are some of the easiest ways you can identify a grassy weed invasion.

Look For These In Your Lawn:

  • Taller growth than the surrounding grass
  • Quicker growth rate
  • Brighter or darker leaf blades
  • Different leaf shapes (rolled, pointed, etc.)
  • Discolored or thin patches of grass
  • Prominent seed heads
  • Shallow, invasive roots
  • Bunching or clumping growth pattern

What Causes Grassy Weeds?

Grassy weeds can emerge and spread due to a variety of reasons. Some of the most common reasons include overwatering, inadequate soil conditions, and improper fertilization. Overwatering, for example, can lead to an increase in weed seeds, and many weeds have high moisture requirements that benefit from excess water. Improper fertilization can cause weeds to grow aggressively since it may cause the grass to become thick and lush, making it more challenging to control the weeds. Grassy weeds also tend to have higher nitrogen requirements, which is why overfertilization can so frequently lead to a weed invasion. Below are some of the most common areas/conditions in which you may find grassy weeds in your yard.

Common Sites Of Grassy Weeds:

  • Shady spots in a yard
  • Areas with poor drainage
  • Overly fertilized lawns/soil
  • Compacted lawns
  • Near sprinkler heads
  • Underneath trees & shrubs
  • Untended borders & beds
  • Generally struggling lawns

Life Cycle Of Grassy Weeds

Like all types of plants, grassy weeds have a life cycle. Understanding the weed's life cycle is crucial in eradicating them and preventing them from ruining your lawn. Certain weeds are spread by rhizomes (underground stems) and/or stolons (aboveground stems), while others are spread primarily through seed proliferation. Grassy weeds can have deep taproots, shallow and fibrous roots, or a combination of both. Understanding how and when these weeds develop will help you anticipate and prevent them!

Annual Grassy Weeds

Annual grassy weeds complete their life cycle within one year. They tend to have a short germination period and can quickly invade a lawn, growing rapidly in the warm months before dying off in winter (in cooler climates). Most annual grassy weeds produce seeds that are dispersed every season and remain dormant in the soil until the right conditions are present for germination. These plants tend to thrive in areas with ample sunlight, fertile soil, and plenty of water. Annual grassy weeds only survive for one season and do not have enough time to develop overly complex root systems.

Perennial Grassy Weeds

Perennial grassy weeds live for two or more years, and they can often thrive throughout multiple seasons. While some perennials can survive unfavorable conditions, such as drought or freezing temperatures, others thrive under more favorable conditions with plenty of sunlight and moisture. Perennial grassy weeds often reproduce by using underground root systems to spread from one area to another. Surviving through multiple seasons means these weeds have more time to develop deeper roots and stems that spread all across your lawn. Many perennials spread by both roots and seeds, making them a very formidable foe!

How To Prevent Grassy Weeds


Preventing invasions of grassy weeds is the ultimate goal for any homeowner who cares about their lawn. The most successful approaches in preventing weeds include regular maintenance, good drainage, and proper fertilization. Proper lawn care will make it more difficult for weeds to establish themselves when done consistently. Tasks as simple as proper watering and regular mowing help keep weeds in check because most weeds seek out properly maintained lawns and soils. Below are some of the best practices for avoiding weeds, and be sure to check out Little John's Lawns for the best defense against weeds in Arizona!

Weed Prevention Tips:

  • Fertilize Properly - Too much nitrogen in your lawn is a common cause of grassy weeds, which is why fertilizing properly is so important.
  • Water Deeply - The shallow roots of grassy weeds get first access to water, so longer watering sessions give your lawn a chance to hydrate.
  • Mow High - Allowing your grass to grow slightly taller than normal can help crowd out any weed seedlings that try to emerge.
  • Aerate Compacted Soil - Aeration decompresses compacted soils, which allows your lawn to thrive and crowd out harmful weeds.
  • Overseed - If your lawn develops thin or bare patches, overseeding can create dense growth that can withstand an invasion.
  • Use Mulch - Mulching your garden beds and soil can help to reduce the spread of grassy weeds by preventing them from emerging.
  • Apply Pre-Emergent - Pre-emergent is best applied in spring when young seeds are still germinating.
  • Utilize Lawn Care Services - Professional lawn care and weed removal is always the safest and most effective way to maintain a healthy lawn!