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Controlling Weeds with Herbicides

Spring is rolling in. Trees are starting to bud. The grass is starting to turn green. You're getting the mower ready. You go out there for the first mow... and you're cutting nothing but wild onions and weeds.

You're probably thinking, "I can't wait for another month when my lawn will be lush and onion free." Weed prevention takes a lot of work, and we know how intimidating all the herbicides lined up at Lowes, or your local Co-op, can be. We're here to give you a little more confidence in tackling your weeds and picking out the right herbicide.

We're going to give a brief overview of the most common weeds, the difference in all the herbicides on the shelf, and when to apply what to help you achieve a healthy, weed-free yard.

Types of Weeds

Let's go to the root of the problem. A weed can be any kind of vegetation. There's nothing out there that specifically says which species of plants identify as weeds and which don't. By definition, a weed is any plant that is unwanted and growing in a certain area. For the purpose of this article, we are going to talk about types of weeds that most people find in their yards:

  • Broadleaf weeds like dandelions
  • Grassy weeds like Crabgrass
  • and Grass-like weeds such as wild onions

Types of Herbicides

There are a lot of herbicides out there. Lowes has a whole aisle dedicated to it in fact. So which one is best for you? Let's break them down into different categories so you can better understand them.

Systemic Herbicides - When you see this word, it means that the active ingredients in the herbicide are absorbed through the roots and foliage of the plant. This kills the plant from the inside out. Systemic herbicides may take a little longer to take effect but will end up killing the entire plant, from the flower to the roots.

Contact Herbicides - Opposite from the Systemic type herbicides, contact herbicides kill the plant from the outside in. When applied, the active ingredient prevents the plant from feeding itself through photosynthesis. This attacks the vegetation of the plant and still leaves the root system alive. Most people like contact herbicides because that are fast acting. Some brands like RoundUp have a combined formula of Systemic and Contact Herbicides.

Selective Herbicides - Selective herbicides are one of the best ways to treat weeds that are occurring in your already established yard. This type of herbicide is primarily designed to kill broadleaf plants like dandelions. Just like the name suggests, they specifically target certain plants. One of the most common selective herbicides is known as 2-4-D. Note: new grass that is not completely established yet can still susceptible to broadleaf herbicides.

Nonselective Herbicides - The opposite of selective herbicides, nonselective herbicides target every kind of plant they come in contact with. This type of herbicide is ideal for preparing an area for planting a garden or attempting to establish a completely new lawn.

Pre-emergent Herbicides - Used to target plants before the seed begins to germinate. It's ideal for early spring application before everything starts to green up. Always read the label; pre-emergent herbicides can damage some ornamental grasses that are desirable.

Post-emergent Herbicides - Can you see a trend yet? The opposite of pre-emergent herbicides is the opposite of post-emergent herbicides. They are designed to attack already established plants. Fun Fact: all contact herbicides are post-emergent herbicides. Apply later in the growing season but make sure it's before the weeds go to seed!

Pro Tip: Timing is key to pre-emergent and post-emergent herbicides. If timed properly, you'll only need one during the year. Usually doing both is a waste.

Timing Your Weed Control

You're now basically the smartest person about weed prevention at the neighborhood BBQ. You know all the technical terms, the different weeds, and what each herbicide does. But let's talk about timing, because we know timing is everything.

Early Spring

So it's early spring. You spot the smallest bit of green coming up after a dark gray winter. Time to inspect. Take a look at your yard and see what is going on. No weeds yet? It's probably a good time to go ahead and get some pre-emergent herbicide mixed with fertilizer to apply with a broadcast spreader. This should take care of annual weeds like crabgrass that usually begin to grow in the spring. A good rule of thumb is to apply pre-emergent before the dogwoods begin to bloom.

Late Spring

The grass is green now and you've already knocked out a could of mowings. Inspect your yard. You may have accidentally missed some spots with your pre-emergent and have some new weeds coming up. That means it may be time to get out the post-emergence herbicide. If the weeds you see are not broadleafs, then you may have to resort to removing them by hand.


After having a good-looking yard for the mowing season, it's time to treat your yard one more time with a selective herbicide. This will help prevent as many weeds coming up next spring.

Pro Tips:

  • Avoid spraying herbicides when the temperature is about 90°F; and below 40°F;
  • Avoid spraying herbicides on windy days
  • Avoid spraying herbicides with rain called for in the next 48 hours
  • Always read the label

Weeds can come up for all kinds of reasons. Underwatering, high traffic, compaction, and poor nutrients can play an important role. Taking some weed preventing precautions will help you save money on some of the herbicides listed above.

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