How to Identify Weeds

Many gardeners have difficulty determining what is a weed and what is a vegetable. We all love growing plants and just about any sign of new green is welcome. The idea of unnecessarily pulling, digging, or spraying a valuable garden plant is painful. In an effort to positively identify the suspect, we’ll let it grow to large size through delay and procrastination. A major problem arises because bigger plants can often present bigger problems like large roots, reseeding potential, interference with companion plants, and difficulty in removal.

Can you spot the weeds among the lettuce?

Weeds can dominate a gardener’s chore list if not dealt with early in their life cycles. It’s easier to pluck small, tender seedlings than it is to remove a long taproot that can grow into new plants if not completely eliminated. Spraying herbicide on weeds will often kill them, along with neighboring plants that you wish to keep alive. The whole world of weeds is a pain in the overalls especially when we think we don’t know how to tell which plants are weeds.

Weed identification begins with garden plant identification. There are thousands of plants that we typically consider weeds, but you don’t need to learn even a fraction of them. There are far fewer plants that we cultivate in our gardens; it is much easier to learn what they look like. Learn what a cucumber, corn, squash, pea, radish, lettuce, and carrot seedling looks like and you’re well on your way to learning weed identification.

The basic premise is that you become familiar with the plants you’re intentionally growing. If anything else pops up next to your chosen few, it’s a weed.

These three little plants are not asparagus or rhubarb

Use my definition:  A weed is any plant growing where you don’t want it. You’ll find other sources that classify weeds as “wild” plants competing with “cultivated” plants, but I think that is too limiting. If something is growing where you don’t want it to, you need to move it, remove it, or kill it; it’s a weed.

How do you know what a cucumber seedling looks like? The answer is to sow cucumber seeds in a discernible pattern. As they grow you’ll see the small plants lined up as you planted them. Those are the cucumbers.

Cucumber seedlings

Want to learn about green beans? Grow green beans. You’ll see a collection of plants growing at the same rate because you planted them at the same time.

Green bean seedlings

Weeds don’t follow the same guidelines of cultivation. They grow haphazardly. They grow to different sizes and shapes and colors. They’ll often be grouped into a small space where their seed pod landed. Or they’ll be widely scattered. There is no recognizable pattern to weed growth, which makes them easy to spot if you design your plantings in a recognizable pattern.

As you care for your seedlings, transplants, and established plants, remove any invaders before they become established. It may be Milkweed, Spurge, Purslane (my nemesis), Sorrel, or Thistle that moves in. While experienced gardeners can often identify such culprits it really doesn’t matter as they are plucked from the soil. Pull them early and pull them often. Keep your garden bed for your intended plants only.

Eventually, as you maintain this basic regimen, you’ll become familiar with which plants are the most common weeds in your garden. You pluck them from your beans and peas and then you’ll see them among your daisies and poppies. You won’t have to struggle deciding if it’s a weed or not, you can be confident in eliminating the threat.

Of course keeping up with the attack of weeds can be daunting. Use that to your advantage. When one of your beds is overrun, remember what the attackers look like when you eventually deal with them. This can help in their identification in other beds.

The weeds to the left of raspberries are common in my garden (some are in the lettuce above)

While you can handle the anonymous weed threat forever, there may come a time when you need to learn more about pernicious attackers. A few years back I had an infestation of a particular weed that consumed great amounts of my time. While I try to avoid using herbicides in my garden, they can be effective when needed. But specific herbicides are only effective against specific types of plants. That’s when you need to identify your weed.

The internet, reference books, local Extension offices, and experienced gardeners can all help you identify a plant. In my case I learned that my weed nemesis was “Purslane”. The waxy leaves, low growth pattern, and green-purple color became very easy to spot in the garden. I learned that purslane is edible and is often cultivated by gardeners as a salad plant. I also learned that it is resistant to many of the herbicides I would have used on it. The best method of eradication was pulling or cutting it before it seeded.

Purslane among onion seedlings

When I moved to a new house,  I started a new garden with many transplants I dug up from my previous garden. Before long I noticed the tell-tale Purslane emerging among some of these plants. I acted quickly and mercilessly. No Purslane was allowed to live and my garden is now completely Purslane-free. The problem was eliminated because I only allowed specific plants in my beds and I learned to identify a specific threat.

Pay attention to everything in your garden. We typically don’t sow seeds in our garden paths. If something begins popping up between our stepping stones or through the mulch, it is a wild plant that was sown by wind or birds or was lying dormant in the soil for untold years. Take a few seconds to make a mental image in your mind and store it in your brain’s “weed file”. The next time you see that plant in a garden bed you won’t need to hesitate. It’s a weed.

Even plants you place intentionally can become weeds. Remember, a weed is any plant growing where you don’t want it. You want them in your garden, but they can self-sow or spread to an area that isn’t part of your plan. Once they interfere with other plants and you don’t like their location, they’re weeds.

You’re probably more familiar with this category of plant so identification can be easy. My Lamb’s Ear (Stachys byzantina) is nice to look at and fun to feel, but one section has overrun my Knautia and Salvia. It’s turned into a weed and needs to go. Lucky for me I can easily tell the offending plant from the others I’m trying to save because it’s one I planted on purpose. The Knautia in this bed is also beginning the march into other areas. Right now it’s a valued plant but I recognize that it will become a weed once it escapes into nearby plantings.

This Lamb’s ear has become a weed

You don’t need to know the name of the weed you confront. We all know what Dandelions look like, but many of us don’t know the name Prostrate Knotweed, a plant that many gardeners have and instantly pull as a weed. I have it, I pull it, and I only recently learned the name.

Identifying weeds can be quite easy, but identification doesn’t imply knowledge about the nomenclature, history, cultivation, and life cycle of a plant. You don’t need to know the name to identify a plant as a weed.

Don’t delay dealing with a problem plant while you learn about it. Know the plants you want in your garden. Learn about their cultivation and maintenance needs; know their nutrition and fertilization requirements; know their names. Realize that any plant interfering with your garden is a weed. You can learn its name after you remove it.


2 responses to this post.

  1. great post


  2. Have a look at this program identfying weeds. It is by far the most comprehensive guide on weeds compared to any book. It is on a Botany Professor’s site and it’s called Recgnizing the 1200 Weeds of America and Canada.


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