Identify Grass Weeds

R. L. Rhodes
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A weed can be any invasive plant that forces its way into your landscape, occupying space that could be inhabited by other plants. Some weeds are broadleaf; those with narrower leaves are often called grass weeds. When tending your lawn, some of the most persistent and difficult to spot weeds are those that resemble or are, themselves, species of grass. In fact, some can even be desirable grasses when they’re not invading an already established lawn.

Structural elements

When identifying grassy weeds on your lawn, it helps to be familiar with the structure of turfgrass in general. From the ground up, the body of a grass plant is made up of its roots, stem, leaves and seed head.

Image: Ed Luschei

Spike-type seed-head on yellow foxtail.

Image: Matt Levin

Panicle seed-head on bentgrass.

The seed head can be helpful in identifying grass types, but usually gets lopped off when you mow your yard, so may not be available. If some portion of the grass in your yard is full-grown, you can look for differing types of seed head described as panicle, spike and receme. Foxtail, for example, is easily identified by its characteristically bushy seed head. That structure, with its cluster of seeds called “spikelets,” is referred to as a spike. Panicle seed heads are like miniature trees—a central stem with the spikelets growing at the end of branches. By contrast, the spikelets on the raceme type seed heads grow unbranched.

The leaves make up most of what we think of as turfgrass, and they can be divided into three parts: the sheath, the collar and the blade. Differences in the shape of the blades can help us distinguish between varieties. If you place a blade of grass on a flat surface, some will lie flat while others are keeled like a boat. Some are glossy underneath while others are matte. And some have a single mid-vein running down the length of the blade while others are ribbed with multiple small veins.

Image: Harry Rose

A grass stolon.

Botanists use the word “vernation” to describe the growth and arrangement of new leaves on a plant. In cool-season grasses, vernation can be either folded or rolled. You can check the vernation of your grass by cutting a cross-section and looking at the newly formed leaves beneath the collar, or by trying to roll a shoot of grass between your fingers. If the shoot flattens, it likely has folded vernation.

Finally, we can talk about how grass plants propagate. Some use rhizomes, underground shoots that spring up elsewhere to produce new plants. Others use stolons, which are a like above-ground rhizomes that put out roots at intervals along its length. Some use neither rhizomes nor stolons, but reproduce in tufts-like bunches.

Keeping those structural features in mind will help you distinguish between different types of grassy plant.

Weedy grasses

Below are some of the most common types of grassy weeds found in the United States. Use this table to help you identify some of the invasive grasses in your landscape.

Type of grass

Seed head

Leaves

Vernation

Propogation

Annual bluegrass Panicle Ribbed, keeled, pointed blades Folded Bunches
Barnyardgrass Panicle with hairy spikelets Smooth, flat, with a thick mid-vein and rough edges Rolled Bunches
Bentgrass Panicle Narrow, ribbed, flat Rolled Stolons
Crabgrass Multiple, fingler-like spikes Wide, pointed blades Rolled Bunches
Quackgrass Spike Smooth, broad, pointed blades Rolled Rhizomes
Witchgrass Broad, broom-like panicle Flat, hairy, pointed blades Rolled Bunches
Yellow foxtail Yellow “foxtail” of spikelets Flat, base fringed with whitish hairs Rolled Bunches

If you’re unsure whether or not your sample matches, or suspect that you have a less common variety of grassy weed, take some samples in to your nearest Extension Service office and let the experts take a look.

Once you’ve identified a grassy weed in your lawn, head to the Home Depot for weed-fighting solutions. And keep current with the Garden Club for more articles in our series on the right lawn care for your grass type.

Got questions about this article or any other garden topic? Go here now to post your gardening ideas, questions, kudos or complaints. We have gardening experts standing by to help you!


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