Does Fertilizer Kill Weeds? What You Need to Know!

Isn’t it nice when a product or tool does more than one job?

Two-in-one shampoos,  Swiss army knives,  mop slippers, hats with headphones, sporks, bottle openers in just about everything…

The problem is, they can be hit or miss when it actually comes down to how useful or practical they are.

The same can be said for fertilizers that also contain herbicides.

Does fertilizer kill weeds? Yes and no – is the answer.

In this article, we take a look at the pros and cons of using weed and feed combos, or if you should just stick to a dedicated product for each job.

Without further ado, let’s get started.

Will Fertilizer Kill Weeds? The Quick Version

Time, as they say, is money. And in the interests of saving you both, here’s a brief summary of this article for anyone in a rush.

Fertilizers are designed to stimulate plant growth, so anything green can enjoy a health boost, develop stronger roots, lush, vibrant leaves, and – if applicable, bear a quality yield of fruits/vegetables.

lawn fertilizer in bag

And that includes weeds. As such, most fertilizers will not prevent weeds from growing – but rather do the opposite.

A fertilizer that kills weeds doesn’t exist, but rather incorporates a weed-killing formula with the food.

I am, of course, talking about the many popular weed and feed products that claim to help desirable plants, simultaneously preventing or killing the unwanted stuff.

But do they actually work? Stay with us, as we take a look in more detail.

Weed and Feed Products – What Are They?

Sometime in the late winter/early spring, you’ll see them appear in big box stores and garden centers.

Shelf after shelf overflowing with products claiming to feed your flowers/lawn – and kill or prevent weeds at the same time.

Companies like Scotts, Spectracide, BioAdvance, Miracle Gro, and Preen are some of the most popular – and they offer several variations of the same thing – enough to make your head spin.

Designed for use on lawns, flower beds, or vegetable patches, weed and feeds are all the rage as they try to kill two birds with one stone.

Or rather, let one bird live and “take care” of the other.

Most of them will contain synthetic plant fertilizers, AND a pre-emergent, selective, residual herbicide – depending on the type of product.

This means that it’s designed to prevent new weeds from growing, without harming existing or future desirable plant life, and that it works by remaining in the soil for an extended period of time.

Pre-emergent weed and feed products work by forming a barrier after being activated by water. This barrier stops undesirables from poking through.

As such, weed and feeds are typically applied in the spring, before the main growing season has begun.

However, products are available with selective post-emergent herbicides (with feed) that eliminate weeds that have started to show above ground later in the year.

At the same time, weed and feeds contain a plant food that typically offers a mix of nitrogen, phosphorus and/or potassium – at various percentages relative to each individual product.

The option you choose will depend on many factors – but most importantly the type of soil and grass you have in your region.

This article on the different types of lawn fertilizers will tell you more, and go here for a full guide on the different types of weed killer if you need to brush up on your herbicide jargon.

person in yellow gloves holding granual fertilizer

Weed and Feed Advantages

It’s not rocket science here –  the main plus point for using weed and feeds is the time and effort they’re going to save you from laying down two separate products.

And we all like things that make life easier, right?

Aside from that, you’ll also save a decent amount of money – which is a major advantage when striving for a beautiful lawn and garden, as costs can quickly add up.

But does lawn fertilizer kill weeds? Are they going to actually do the job we purchase them for?

Read on to find out.

Do Weed and Feeds Products Work?

Used correctly, weed and feeds can be beneficial to some homeowners and might show less than impressive results to others.

Either way, if you’re starting a new flower bed, or trying to give your lawn a boost, it might be worth trying a weed and feed early in the season.

It can be very effective at controlling broadleaf weeds, for example, before they’ve had a chance to rear their unwanted heads.

This piece on tackling dandelions in your lawn might also give you some species-specific tips for dealing with those pesky plants.

However, for weeds like crabgrass, you need to choose something more specific. Alternatively, you can check out this article on how to deal with crabgrass naturally.

Regardless of the weeds you’re looking to prevent/control, there’s no doubt a weed and feed is going to give your lawn a quick boost at the start of the season – from the fertilizer point of view.

But therein lies the problem.

Weed and feeds are generally designed to achieve fast results, but they can fail to get to the “root” of the issue. Turfgrasses, for example, need long-term help to see them through the season.

Not just a quick fix at the beginning of it.

Ask any wife/girlfriend/lover/professional hairdresser which is better – a two-in-one shampoo/conditioner, or a dedicated bottle of each?

I’ll bet my bottom dollar it’s the latter. Heck, if I tried to convince my wife otherwise, I’d probably be murdered.

As such, I highly recommend choosing a separate product for each requirement in your garden, treating as and when necessary throughout the year, and not just relying on a brief health boost in the spring.

Pick up a proven, dedicated lawn fertilizer – with the sole job of improving lawn health. Look for something that breaks down slowly to feed your lawn the nutrients it requires over time.

And then choose/try a weed-control method that you think would work best for your particular needs.

But that being said, by all means, try a weed and feed at the start of the season, and there are some top tips coming up for how best to do so.

person fertilizing lawn with liquid fertilizer

Weed and Feed Tips – How to Get the Best Out of the Combo

If you’d prefer to go down the weed and feed route, I’ve included a few extra tips and tricks for getting the most out of your two-in-one product.

  • Get the timing right - apply the product around the same time that your lawn needs its first cut of the season. The last week of March is a rough guide to shoot for.
  • Ensure good coverage - one of the reasons weed and feeds fail is that not enough or too much product is laid down. Use a broadcast spreader or one of these tow-behind spreaders for larger areas.
  • Remember to “activate” the product by watering it in - but not so much as to wash it away.
  • Don’t overfeed - a second application isn’t going to help control weeds you’ve missed, and will damage the area. Either use a post-emergent weed killer correctly or wait until fall.
  • Always follow the instructions for the latter.
  • Manage your expectations - make sure the product you choose is designed to kill/control the weeds you have, or will potentially have if left untreated.

Finally, be patient. Remember that weeding and feeding is a cyclical, long-term process, and achieving your dream lawn can take several seasons.

Should I Fertilize or Kill Weeds First?

When you’re putting together your lawn-care/garden maintenance schedule, it’s important to get treatments in the right order.

And if you’d rather use two separate methods for killing weeds and boosting your lawn health, then you should always be weeding BEFORE feeding.

Remember, a good plant fertilizer is going to nourish anything green - which includes weeds and undesirable vegetation.

It stands to reason that you need to remove or kill what you don’t want before feeding whatever remains. So be smart about choosing the right option from the different types of weed killers available.

How to Fertilize Your Lawn and Kill Weeds

A dedicated lawn fertilizer won’t kill or prevent weeds on its own, but it can be a very powerful weapon in keeping them at bay - with the right technique.

The more healthy grass your lawn has, the less likely you’ll see a weed infestation - as the soil won’t be big enough for the both of ‘em.

Think of it as an arms race. You supply the grass with weapons, while denying the weeds supplies.

Use grass fertilizer to create healthy, strong roots, promote thick growth, and the grass will crowd out other plant life. Your lawn will become a hostile place for weeds - and they should stay away.

Thus winning the turf vs weed war.

But should you use a liquid or a granular fertilizer for your lawn? Thank link will tell you everything you need to know.

granual lawn fertilizer

And there are alternatives to using chemicals or other liquids/granules on your lawn.

Another excellent method for weed control in your lawn is to aerate it. Lawn aeration is an often-overlooked practice that is an essential part of the care schedule for the very best lawns.

It can help with surface drainage, and boost nutrients to the grassroots - which in turn will strengthen the plant and increase its chances of choking out undesirables.

This article on the top seven benefits of aerating your lawn will tell you more and go here to explore the best aerators if you’re already convinced, and you want to get started.

When NOT to Apply Weed and Feed

As well as offering advice on when and how to apply weed killers and fertilizers, it’s also worth noting when you should NOT apply them.

As a rule of thumb, you shouldn’t be doing either more than twice a season. Unless, of course, you’re spot treating weeds with a post-emergent herbicide (follow that link for some good options).

Even then, you need to wait at least two months between applications - or risk overloading the area with chemicals, and causing environmental damage.

And with fertilizer, you can have too much of a good thing, and end up “burning” your desirable plants.

This article on how often to apply fertilizer will tell you everything you need to know, so you don’t end up overfeeding your garden.


Can you apply weed killer and fertilizer at the same time?

That’s a great question - and it depends on the product. Some products can be used at the same time, such as some synthetic lawn weed killers and dedicated, slow-release organic fertilizers.

But as a rule of thumb, you should always try to separate the application of products that are designed for different purposes.

You’re not going to miss out on much by waiting a week after dispensing a herbicide before applying your fertilizer.

For more info, watch the informative video, below.

Does fertilizer go bad?

Gardeners are always concerned about the shelf life of different products, in order to understand if they should apply them in a timely fashion, or if they can sit in the shed for a couple of seasons.

But does fertilizer go bad? Follow that link to find out.

How do I get rid of my lawn full of weeds?

It can be pretty heartbreaking, seeing what could be a lush lawn overtaken by undesirable growth.

Thankfully, there are many methods, techniques, and products you can use to reclaim your grass.

You can also head over to this article on the best lawn care tools for equipment to help you with the process.

But one of the best methods for weed control in lawns is to practice overseeding. Follow that link to learn how.

How long does it take for fertilizer to kill weeds?

So long as you’re using a weed and feed fertilizer (fertilizer on its own is going to help weeds as much as any plant), you should see results within a week.

However, it depends heavily on the product used, the type of weed, the extent of the infestation, the conditions, and other factors.

You might not see total eradication for several weeks, and/or after several applications. And in some cases, the product might not work at all.

Trial and error, my friends, trial and error.


Does fertilizer kill weeds?

Yes and no - it can be useful at certain times during your garden-maintenance calendar - providing you’re using a weed and feed combination. But fertilizer on its own is going to feed anything green.

If you really want to kill weeds and feed lawns - you need a dedicated product/method for each.

Let us know your thoughts on the subject. Have you had success with a two-in-one formula? Which method works best for you? Reach out in the comments, below.

In the meantime, stay safe out there - and happy weeding and feeding!

Andy Gibson

My name's Gibson. Andy Gibson. I like to think of myself as the Bond of the backyard, that is if yard work ever became sexy. I write about everything about indoor and outdoor gardening and the dread-it-but-still-need-to-do-it chores around the yard, like cleaning out the gutter guards.

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