Steps to identify a weed

by Stephanie Suesan Smith on May 4, 2011

One of the things I spend a lot of time doing every spring and summer is identifying weeds for people.  Now, a weed is just a plant that is growing where it is not wanted.  Sometimes, though, it has to go, and until you know what it is, you do not know how to get rid of it.

Eliminating weeds is important when growing vegetables.  Weeds take up nutrients the vegetables need as well as scarce water.  They shade your vegetables and sometimes produce soil toxins to keep the plants around them from growing so the weeds can steal all the nutrients available.  Finally, weeds such as nettle make harvesting your vegetables a misery.

Weeds in the garden are not usually shrubs or trees, and vines overlap several categories, so I am going to discuss the three most common categories of weeds and how to tell them apart.  In the days ahead, I will cover how to get rid of them so your garden has a chance to grow the plants you want it to grow.

To identify a weed, first try to find one that has flowers on it.  Pull the weed up roots and all if you want to remove it, or at least examine it from head to toe. Try to answer these questions.  You may not be able to answer them all, but each gives clues to finding the plants identity.

  • What do the leaves look like? How are they arranged on the stem?
  • What does the stem look like?
  • Is it woody or green and soft?
  • What do the flowers look like?
  • Is there one flower, or a cluster, or dozens?
  • What color are they?
  • Is there fruit, berries, or other seed pods?
  • What do they look like?  How many per plant?
  • What do the seeds look like?

Once you have all your data, you can classify the plant into one of three broad categories:

  • Grasses — this seems like a no brainer, but consider that grasses range from bamboo to bermuda grass, and that a popular “grass” is actually a broadleaf plant.  Grasses have hollow, jointed stems and long leaves with the vein running the length of the leaf.  Flowers are usually small and hard to see.
  • Broadleaf weeds –Saint Augustine “grass” is actually a broad leaf plant.  Most other weeds fit in this category, too.  They have showy flowers, leaves with veins that run throughout the plant, and the stems are often pithy.
  • Sedges and Nutgrass — the stems of sedges are triangular in shape and have leaves coming from all three sides.  These plants are hard to kill.

If all you want to do is kill it, that is generally close enough.  If you actually want to know what it is, now you begin to refine your search.  The National Agricultural Library, maintained by the United States Department of Agriculture,has a page of resources to help you identify plants.  Aggie Turfgrass has a nice section on identifying lawn weeds that will help you identify weeds in your garden, as well.

One thing that should be noted is that many herbicide products that are labeled for lawn use are not allowed in the vegetable garden.  Because you are going to eat the produce, the products have to meet a higher safety threshold to be used around your vegetable plants.  Always read and follow product labels before using.  You do not want to end up poisoning yourself and your family in an attempt to kill the weeds.

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{ 8 comments… read them below or add one }

Julie May 4, 2011 at 5:27 pm

I can really appreciate your post. I’ve been learning about gardening, invasive plants, lawn care, etc… for the past three years because I write a weekly newspaper garden article with the director of our university’s Garden during the spring/summer. I by no means have a green thumb, but I’d say it’s slowly turning green. The topic of the week here is the brown marmorated stink bug. I’m not looking forward to that insect’s arrival!
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Stephanie Suesan Smith May 5, 2011 at 6:50 am

Sounds like a fun job. I enjoy writing about gardening or dogs the most, but write about any nonfiction topic, so understand the learning curve you are climbing.

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Alexandra May 8, 2011 at 7:36 am

Glad I discovered your blog! I just posted, yesterday morning, a photo of my garden. Now I’m working on the veggies. You are so right to point out that herbicides can be dangerous. In fact, I have learned to avoid them altogether. We have a sole-source aquifer on Cape Cod and anyone using herbicides endangers drinking water. Academic science shows that even traces can be dangerous to humans and pets. Have you seen the documentary A Chemical Reaction about a town in Canada that banned herbicides for landscaping purposes? That was 20 years ago. A similar ban was enacted elsewhere in Canada and two years later the water in streams, rivers and ponds is of better quality. The chemical industry wants to sell its products but they are not really any better for people than for weeds. “Cides” comes from the Latin TO KILL. I look forward to reading more. Like, for instance, something has been eating the leaves that have sprouted on my gaura. Any suggestions of how to deal with that problem? Thanks.
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Stephanie Suesan Smith May 8, 2011 at 7:48 am

You need to find the pest and identify it. That will give you an idea of what to do to kill it. Even organic methods rely on knowing what pest is causing the problem to deal with it.

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jay west June 10, 2011 at 12:22 am

Your best bet against weeds is to cultivate a healthy lawn. Proper watering, sufficient nutrients and regular aeration are the keys to a strong and healthy lawn; a weed puller can do the job well too.

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Stephanie Suesan Smith June 10, 2011 at 7:19 am

I agree with that. However, I am always getting questions about how to identify a weed, or how to kill one, so people need to know what they are trying to crowd out.

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Jimmy July 30, 2011 at 9:50 am

You know, not being able to properly identify weeds is actually the main reason why I never got into vegetable gardening. The first time I tried to grow my own vegetables, all the weeds came up too and I had no idea which was a good plant and which was a weed and the weeds eventually just took over. I should probably give it another go. I hate giving up. It’s too late this year though.
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Stephanie Suesan Smith July 30, 2011 at 9:54 am

You can plant a fall garden if you want.

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