Prevent Weeds with Pre-Emergent Fertilizers

By: Ken Wilson

Weeds are fast growers; if you see a few in your lawn, you’ll likely get a lot more. Weeds are resilient and grow quickly, so keeping them from sprouting is essential. One solution to get rid of them is using a pre-emergent fertilizer. But what is a pre-emergent fertilizer, and how can homeowners use it to eliminate weeds?

Pre-emergent fertilizers are herbicides that prevent weeds by stopping the enzyme that controls germination. This fertilizer does not stop germination entirely but does prevent the weeds from popping up on your lawn. This product is also often referred to as weed and feed.

Weed and feed are popular options for homeowners who want to take a proactive approach to killing weeds. Pre-emergent fertilizers do not kill existing weeds but keep them at bay. The key to using this fertilizer is to use it at the right time. When applied to your lawn during the wrong season, you may be left with a yard full of weeds and a product you can’t use.

What is a Pre-Emergent Fertilizer?

This type of weed killer is a combination between a herbicide and a fertilizer. It’s also called a pre-emergent herbicide or weed and feed. Pre-emergent herbicides aren’t always combined with fertilizers, so it’s important to check that you’re purchasing the right product to eliminate weeds.

Weed and feed generally contain dithiopyr, nitrogen, phosphorus, and potassium. It’s available in liquid or granule form and sometimes has additional ingredients. It’s a dual-purpose product aimed at killing weeds before they reach the surface while fertilizing your lawn at the same time.

This weed killer kills broadleaf weeds like chickweed, dandelions, and clovers, but you may need to apply additional products for other weeds, like crabgrass. Before applying a pre-emergent herbicide, it’s essential to check if it’s suitable for your lawn. Not all products are ideal for all grass types; purchasing the incorrect product can damage your grass.

Pre-emergent vs. Post Emergent Fertilizers

A pre-emergent fertilizer inhibits weed growth before germination, and it’s a preventative approach to stopping weeds. Once weeds have sprouted, this type of inhibitor can’t kill them.

Post-emergent herbicides are used to get rid of surface-level weeds. This herbicide is applied during the spring and summer seasons to keep the lawn free from weeds.

Do Pre-Emergent Fertilizers Work?

This combination of herbicides and lawn feed can work if it’s applied during the right time. Most homeowners use weed and feed in the Spring, but it can be tough to get the timing right since you’re trying to achieve two things: fertilize your lawn and kill weeds.

If you apply it too early, you’ll have a well-fertilized lawn with many weeds. Apply it too late, and you’ll be left with a lawn that hasn’t had enough time to get the nutrients it needs to thrive during the summer.

When is the Best Time to Weed and Feed?

The most suitable time to treat your lawn with the pre-emergent is springtime. If you need to re-apply, don’t re-apply during the Spring or summer. Instead, wait until Fall so your grass has time to recover. If your lawn has been seeded recently, it’s best to avoid weeding and feeding; this will kill the newly sown seeds.

Stick to using pre-emergent products twice a year. Treating your lawn multiple times a year can lead to weed resistance and a chemical build-up in your lawn.

Why a Pre-Emergent Fertilizer Doesn’t Work

There are a few reasons why this weed prohibition may not work. These include the following:

  • Your lawn has become resistant to a particular weed-killing product.
  • The incorrect product is being used for your type of grass.
  • The weeds have already germinated.
  • Not applying the pre-emergent correctly.
  • Applying the fertilizer and herbicide in the incorrect season.
  • Spreading without a proper spreader.
  • Choosing inferior products to use on your lawn. (The cheapest isn’t always the best.)
  • Applying water before or after spreading the weed and feed waters it down and becomes less effective.
  • Pre-emergents only kill broadleaf weeds; if you have other weeds like crabgrass, it won’t work.

How Long Does a Pre-Emergent Last?

This type of weed killer usually lasts between 3-5 months, but some can last longer depending on the type of weed killer. The most effective approach to using the pre-emergent is to apply it and then wait at least two months to re-apply. This ensures maximum effectiveness.

Should You Water After Applying a Pre-Emergent Fertilizer?

You will need to apply water after using a pre-emergent but should avoid watering straight after you spread it on your lawn. Instead, water it within three to five days.

Different types of fertilizers also require different amounts of water. The granules need more water to soak into the lawn, while the liquid variety requires less water. Pre-emergents should also never be applied to a wet lawn. Avoid watering and wait until your grass is dry before using the pre-emergent herbicide.

Tips on Using Pre-Emergent Fertilizers

Using weed and feed is easy as long as you follow the manufacturer’s guidelines. But there are a few other things you may want to keep in mind before using it on your lawn:

18-24-12 is used to enrich phosphorus-deficient soils, and it is also effective in establishing strong root systems, which, together with the nitrogen content, makes it such an effective new lawn fertilizer.

  • Check the weather before you apply the fertilizer and herbicide. Pick a clear, warm day and avoid spreading on windy or rainy days.
  • Use a drop or broadcast spreader for better precision instead of spreading by hand.
  • Keep children and pets away from the lawn after using the weed and feed.
  • Avoid applying lawn seeds before or after you cover the lawn with the herbicide and fertilizer combination.
  • Start at the perimeter and work towards the center when spreading the herbicide. Make sure you move forward and backward in parallel lines.
  • Avoid watering straight after you apply the pre-emergent to your grass.
  • Rotate the types of products you use to combat weed resistance.
  • Make sure your spreader is calibrated correctly to ensure accurate application.

Final Thoughts

Pre-emergent fertilizers are effective in killing weeds when applied at the right time. It’s essential to choose a good brand of weed and feed and rotate between products so you don’t end up with weeds that are resistant to herbicides. To get the most out of this weed killer, follow up with a post-emergent fertilizer to keep your lawn weed-free.

About the author 

Ken Wilson

Long time career in the home services industry from remodeling to patio construction. Currently residing to in SWFL and active contributor to multiple home & garden publications.