RM18 Vs. Roundup: A Head-to-Head Battle of Weed Killers

I’ve spent countless weekends battling weeds in my garden, and I know the struggle of picking the right herbicide to keep those pesky invaders at bay. In this article, I’m comparing two heavy-hitters in the weed-killing world: RM18 and Roundup.

My goal is to break down their features, strengths, and weaknesses to help you decide which one suits your needs. From effectiveness to safety, cost to environmental impact, I’ll walk you through my experience and analysis to make your choice easier.

Let’s get started and find the best tool for your weed-free dreams!

A Brief Comparison Table

My Journey With Weeds

I’ve always loved my garden, but weeds? Not so much. They creep into my flower beds, choke my lawn, and make my driveway look like a jungle. Over the years, I’ve tried everything from pulling them by hand to experimenting with homemade vinegar solutions.

Nothing quite matches the power of commercial herbicides like RM18 and Roundup. But choosing between them isn’t straightforward—each has unique strengths, and I’ve learned the hard way that picking the wrong one can mean dead plants I didn’t intend to kill or weeds that just won’t quit.

So, I decided to put RM18 and Roundup to the test, comparing their features, effectiveness, and quirks to help you make an informed choice.

Understanding RM18: The Fast-Acting Contender

RM18, produced by Ragan & Massey, is a non-selective herbicide, meaning it doesn’t discriminate—it’ll take out any plant it touches.

Its formula combines two active ingredients: glyphosate (18%) and diquat (0.73%).

Glyphosate is the heavy hitter, attacking weeds systemically by traveling through the plant to the roots.

Diquat, on the other hand, is a contact herbicide that burns the foliage on impact, giving RM18 its fast-acting reputation.

I sprayed RM18 on a patch of crabgrass and dandelions in my backyard, and within 12 hours, I could see the leaves wilting—a satisfying sight!

Pros of RM18

• Lightning-Fast Results: The diquat in RM18 makes it act quickly. I noticed visible wilting within hours, which is perfect when you want immediate feedback that your spray is working.
• Soil-Friendly for Replanting: RM18 deactivates once it hits the soil, so you can replant ornamental flowers a day after spraying and vegetables or lawn grasses after three days. I used it to clear a weedy patch for a new flower bed, and I was planting petunias in no time.
• Rainfast in 30 Minutes: Living in an area with unpredictable showers, I appreciate that RM18 is rainproof in just half an hour. No need to stress about a sudden downpour washing away my efforts.
• Broad-Spectrum Control: It tackles over 100 plant species, from stubborn kudzu to poison ivy. I had a wild blackberry bush creeping into my fence line, and RM18 took it out with one application.
• Cost-Effective Coverage: A single gallon of RM18 concentrate can cover up to 31,800 square feet when mixed properly, making it a solid choice for large areas like driveways or patios.

Cons of RM18

• Non-Selective Nature: RM18 doesn’t care what it kills. I accidentally oversprayed near a rose bush, and let’s just say it wasn’t pretty. You need to be precise to avoid collateral damage.
• Limited Residual Control: While it prevents weed regrowth for up to six months, this is shorter than some Roundup products that can last up to a year. I had to reapply in a gravel path after about five months.
• Health and Environmental Concerns: The glyphosate in RM18 has raised eyebrows due to potential health risks, including links to cancer in some studies. I always wear gloves and a mask when spraying, but it’s something to consider if you’re cautious about chemicals.
• Mixed Customer Feedback: Some users, like me, love RM18’s speed, but others have reported it didn’t work as expected on tougher weeds like long grass. I found trimming weeds first helped improve results.

Exploring Roundup: The Household Name

Roundup, created by Monsanto, is the most recognized name in weed killers, and for good reason—it’s been around since the 1970s and has a range of products tailored to different needs.

Its primary active ingredient is glyphosate, with concentrations varying from 41% to 50.2% depending on the formula (e.g., Roundup Weed & Grass Killer Concentrate vs. Max Control 365).

Some Roundup products also include additional ingredients for extended control, but for this comparison, I focused on the standard concentrate, which I’ve used on my sidewalks and around my vegetable garden.

Pros of Roundup

• Trusted Effectiveness: Roundup’s glyphosate formula is a proven weed-killer. I sprayed it on a patch of clover and spotted spurge, and within a week, they were completely dead, roots and all.
• Versatile Product Line: Roundup offers specialized formulas, like Roundup for Lawns, which targets weeds without killing grass. I used this in my front yard, and it spared my Bermuda grass while wiping out dandelions.
• Long-Lasting Options: Products like Roundup Max Control 365 can prevent weed regrowth for up to 12 months, which is great for areas like gravel driveways where I don’t want anything growing.
• Economical for Large Areas: At roughly $15–$25 per gallon of concentrate, Roundup is slightly cheaper than RM18, and it covers up to 25,000 square feet, depending on the product.
• Wide Availability: You can find Roundup at virtually any hardware store, garden center, or online retailer, making it a convenient choice when you need it fast.

Cons of Roundup

• Slower Initial Results: Unlike RM18, Roundup doesn’t have diquat, so it can take 2–48 hours to show visible effects. I had to wait a couple of days to see my weeds browning, which tested my patience.
• Environmental and Health Controversy: Glyphosate’s potential as a carcinogen has been debated heavily. A 2015 IARC study labeled it a “probable human carcinogen,” though the EPA disagrees. I’m cautious and always follow label instructions to minimize risks.
• Soil Persistence: Some Roundup formulas linger in the soil longer than RM18, delaying replanting. I had to wait a week before seeding a new lawn area, which was frustrating.
• Messy Application: The concentrate bottles can be tricky to pour. I spilled some while mixing, which was a hassle, even with safety gear on.
• Emerging Resistance: Some weeds are developing glyphosate resistance, which could reduce Roundup’s effectiveness over time. I haven’t encountered this yet, but it’s a concern for long-term use.

Key Features Comparison of RM18 And Roundup

• Active Ingredients and Mode of Action

RM18’s combo of glyphosate and diquat gives it an edge in speed.

The diquat burns foliage on contact, while glyphosate works systemically to kill the roots.

I sprayed RM18 on a patch of poison ivy, and the leaves were shriveled by the next morning, with the plant fully dead in about 10 days.

Roundup, relying solely on glyphosate in most formulas, takes longer to show results but is just as effective at killing roots.

I used Roundup on a similar patch of poison ivy, and while it took about two days to see wilting, the results were equally thorough after two weeks.

• Speed and Rainfastness

RM18’s 12-hour wilting and 30-minute rainfast time make it ideal for quick jobs or areas with frequent rain. I sprayed it before a storm rolled in, and it held up perfectly.

Roundup’s rainfast time varies (10–30 minutes), but its slower visual results—sometimes taking a couple of days—can feel less satisfying if you’re impatient like me. Still, both products deliver when you give them time.

• Replanting Flexibility

RM18 shines here. Its soil deactivation means you can plant flowers the next day or vegetables in three days. I cleared a weedy spot for a tomato garden and was planting within a week.

Roundup’s replanting timeline depends on the product—some allow planting in 1–3 days, while others, like Max Control 365, require waiting up to a week. This makes RM18 better for projects where you want to replant quickly.

• Coverage and Cost

RM18 covers more ground (up to 31,800 sq. ft. per gallon) compared to Roundup’s 25,000 sq. ft. for most concentrates. However, Roundup is often cheaper, with generics like Compare-N-Save dropping the price even lower.

I found a 2.5-gallon jug of Roundup for about $50, while RM18’s 2.5-gallon jug cost me closer to $65. If you’re treating a large area, RM18’s coverage might justify the extra cost, but for smaller jobs, Roundup’s price is hard to beat.

• Environmental and Safety Considerations

Both products contain glyphosate, which has sparked controversy.

Studies, like one from the IARC in 2015, suggest glyphosate may be a carcinogen, though the EPA’s 2020 review found it unlikely to cause cancer when used as directed.

RM18’s diquat adds another layer of concern, as it’s toxic to aquatic life and can irritate skin or eyes.

I always wear protective gear—gloves, long sleeves, and a mask—when using either product.

RM18’s soil deactivation is a plus for reducing environmental impact, but both require careful application to avoid harming beneficial plants or wildlife.

Practical Applications: Where Each Shines

• RM18 in Action

RM18 is my go-to for quick, dramatic results. I used it to clear a gravel walkway overrun with crabgrass and dandelions. The weeds were visibly dying within hours, and I didn’t see regrowth for nearly six months. It’s also great for lawn replacement projects.

Last spring, I wanted to redo a patchy lawn area, and RM18 cleared it out fast, letting me reseed in just three days. However, I learned to shield nearby plants with plastic—sheeting is a lifesaver to prevent accidental overspray.

• Roundup’s Versatility

Roundup’s range of products makes it adaptable. I used Roundup Weed & Grass Killer Concentrate to prep a vegetable garden bed, and it wiped out everything without leaving the soil unusable for too long.

For my lawn, Roundup for Lawns was a game-changer—it targeted broadleaf weeds like clover without harming my grass. If you’re dealing with hardscapes like patios or driveways, Roundup Max Control 365 offers up to a year of weed prevention, which I found perfect for my concrete patio.

My Personal Experience: Testing Both Products

To get a real feel for RM18 vs. Roundup, I conducted a side-by-side test in my backyard. I had two identical patches of mixed weeds—crabgrass, dandelions, and some sneaky poison ivy.

I sprayed RM18 on one patch and Roundup Weed & Grass Killer Concentrate on the other, following label instructions for mixing and application.

• Day 1: RM18’s patch showed wilting by evening, with leaves curling and browning. Roundup’s patch looked unchanged, which was a bit disappointing.
• Day 3: RM18’s weeds were mostly brown and crispy, while Roundup’s patch was finally showing yellowing and wilting.
• Day 7: Both patches were completely dead, with roots shriveled. I pulled the weeds easily from both areas, but RM18’s faster visual results gave me instant gratification.
• Month 2: No regrowth in either patch, but I noticed Roundup’s area stayed weed-free a bit longer, likely due to its higher glyphosate concentration.

My takeaway? RM18 is ideal when you want quick results and plan to replant soon. Roundup is better for longer-term control or when you need a specific formula for lawns or hardscapes.

Weighing The Pros And Cons For Your Needs

Choosing between RM18 and Roundup depends on your priorities. If speed and replanting flexibility are key, RM18’s fast action and soil deactivation make it a winner. I loved how quickly it transformed my weedy walkway.

But if you need long-lasting control or a product tailored to specific areas like lawns, Roundup’s versatility and slightly lower cost are hard to ignore. I’ve used both successfully, but I lean toward RM18 for urgent jobs and Roundup for ongoing maintenance.

Both come with environmental baggage. Glyphosate’s potential health risks and impact on pollinators like bees make me cautious. I always apply these herbicides on calm, sunny days and keep my pets indoors until the spray dries.

If you’re eco-conscious, you might explore natural alternatives like vinegar-based sprays, though they’re less effective on deep-rooted weeds.

FAQ: Your Burning Questions Answered

Conclusion: Your Path To A Weed-Free Yard

You’ve got a yard to tame, and I’ve been there, staring down a jungle of weeds with a sprayer in hand. RM18 and Roundup are both powerful allies, but they cater to different needs.

RM18’s lightning-fast action and replanting flexibility make it perfect for quick cleanups and garden prep. Roundup’s versatility and longer-lasting options suit those who want tailored solutions or extended control.

Weigh your priorities—speed, cost, or longevity—and always apply with care to protect your plants and the environment. Pick the right tool, and you’ll be enjoying a weed-free yard in no time!