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Mulch can help keep the weeds down, but it can’t halt weeds entirely or stop them forever. That’s when you might have to resort to weed killers like Roundup, but when most hear that brand, there are a lot of negative connotations.
Would Roundup hurt the flowers if it’s sprayed on mulch? Would it reach the weeds? Can you use Roundup on mulch at all?
Roundup is best sprayed approximately 6 inches away from valued plants and at least one week before applying mulch. If Roundup is used on top of mulch, the weedkiller may not reach the soil, run off into the roots of good plants, or contaminate mulch for subsequent years.
It can be a little nerve-racking to use any chemicals you’re unsure of on your flower or vegetable beds that you worked so hard to keep healthy, and we get it. Keep reading to see if using Roundup on mulch will have the effect you want.
Can Roundup be Used on Mulch?
If you have plastic mulch, you should never use Roundup on it, especially if you are reusing it from a previous year and had used weedkiller then. This is common practice with large farms because it helps to stretch the dollar, but it can be risky.
Only Gramoxone is recommended for use on mulch because the sunlight can break down its chemicals. Roundup, however, can be okay if it reaches the soil because it’s usually immediately absorbed into the soil and then broken down slowly.
The issue with plastic mulch is that the Roundup doesn’t easily wash off and may make contact with the root balls of anything you intend to plant in it the following year. Even with organic mulch, such as woodchips, the material is porous and can trap the Roundup or other weedkillers.
That is a result of spraying the weedkiller broadly across the mulch. You might try spraying in between rows, far enough from your valuable plants. Roundup should never be used on food crops like vegetable mulch beds.
The Roundup label should show that the company states not to use Roundup on food crops intended for human consumption. So, if you are using some mulch on your vegetable bed, you’ll need some alternative way to get rid of your weeds to keep your crops safe.
What Happens if I Spray Roundup on Mulch?
Using Roundup on mulch comes with a few complications. For one, the added mulch layer tends to get in the way of your spray, so it can be tempting to spray down the Roundup to an excessive point to make you get to the roots.
You’ll want to resist that temptation, though. On Roundup’s directions, they say right on the label, “do not spray to the point of runoff.” In other words, don’t spray to the point where the excess spray is creating drops and running. That’s an excellent way to get the weedkiller to drip where you don’t want it to go.
A second problem with spraying on mulch is you may end up hurting the wrong plants in the long run. You would want to be careful not to spray the mulch just before the rain would come or on a windy day. The rain can cause the weedkiller to run into your valued plants, and the wind can blow the weedkiller into those same plants while you’re spraying.
When Should I Use Roundup in Mulch Beds?
So, spraying Roundup on top of your mulch won’t have the positive effect(s) you might have been hoping for. If spraying on top of mulch beds isn’t a great idea, what about spraying before applying mulch?
Yes, before applying mulch. This way, there’s no opportunity for the mulch to become contaminated or accidentally spread to plants you don’t want to affect once there’s heavy rainfall.
It’s recommended that you apply Roundup a week before you put on your mulch, spraying about 6 inches away from your valued plants. You’ll need to hand weed if weeds are closer than 6 inches to your plants.
This might sound like a problem if you’ve already laid down your mulch. In that case, you might rake off your mulch, take care of the weeds, and then either reapply your old mulch or apply a new layer.
If that doesn’t excite you, there are a few alternative means of getting rid of your weeds in the section below.
Alternative Ways to Get Rid of Weeds in Mulch
Don’t feel discouraged if removing your mulch is a little more work than you can handle or have the time for right now. Several alternative ways to get rid of weeds from your mulch beds exist.
Using a Hand-Weeding Tool
This first idea isn’t the easiest when there’s mulch in the way, but hand-weeding tools such as the weed puller will pull the weeds up by the roots. With the right tool, there won’t be any need for kneeling on the ground, bending low, or tugging out the weeds.
Using a Black Tarp
Cutting large pieces or strips of black tarp and putting them over weeded areas is effective. Under the tarp, the sun will shrivel up anything underneath. It’s a good short-term solution, but you’ll want to remove the tarp after a few weeks.
You’ll also want to be careful not to accidentally cover the plants you want to keep or shrivel the tops of your plants with the sun’s reflection from the tarp.
Using Boiling Water
If you can get to the weeds when they’re small and more vulnerable, you can kill them with nothing but boiling water. Getting them early is important because the roots won’t be too deep yet. This is a trick commonly used among homeowners to kill weeds that grow between pavers.
What’s the Safest Way of Applying Roundup?
The best way to apply Roundup is carefully! The label on the back will give you more complete instructions, but you want to use the glyphosate with a sprayer, preferably one with an attachable guard. If you have a sprayer that doesn’t come with a guard, you can make one out of a plastic milk carton and a zip tie.
The guard’s point is to help ensure you are spraying where you intended. Glyphosate doesn’t distinguish between weed and flower, so having one of these helpful attachments is almost priceless.
Like we said earlier, you want to spray far enough away from the plants you want to keep alive. Try also to spray close to the ground to prevent the unnecessary spread of the spray. Finally, please don’t turn the nozzle so that the spray comes out as a mist or will blow around too easily. You want a slightly heavier drizzle.
You can see more about applying Roundup safely in the video below.
In Short
Maybe mulch on its own won’t get rid of weeds as you hoped, but the combination of Roundup before applying your mulch will just about obliterate your weed problem. You’ll have to remember to spray the soil around your plants before you put down the mulch layer. Happy gardening!
Sources
- Weed control in flower beds and lawns
- Better Homes & Gardens (bhg.com)
- Lawn Care Forum
- Roundup in my mulch!
- round up on mulch (houzz.com)
- bestmulchingtips.com
- (houzz.com)
- Eco Family Life
- Plant & Pest Advisory (rutgers.edu)