RM18 Vs. RM43: A Gardener’s Guide To Choosing The Right Herbicide

I’ve stood in the garden aisle, staring at bottles of RM18 and RM43, wondering which one will finally tame the jungle of weeds creeping into my yard. Both are heavy hitters from Ragan & Massey, but they serve different purposes.

In this article, I’ll walk you through my experience with these herbicides, breaking down their features, pros, cons, and real-world applications to help you decide which is best for your needs.

Whether you’re prepping a new garden bed or clearing a driveway, I’ve got you covered with a clear comparison.

A Brief Comparison Table

My Journey With RM18 And RM43

As a homeowner with a yard that seems to attract every weed known to humankind, I’ve spent countless hours battling unwanted greenery.

Dandelions, crabgrass, and even sneaky poison ivy have tested my patience.

When I first heard about RM18 and RM43, I thought they were just different bottles of the same stuff.

But after using both, I realized they’re like two different tools in my gardening shed—each with its own strengths and quirks.

Let’s break it down. RM18 is my go-to for quick, targeted weed control when I’m planning to replant soon. RM43, on the other hand, is the nuclear option for areas I want to keep weed-free for a long time, like my gravel driveway.

Here’s how they stack up based on my experience, with all the details you need to make an informed choice.

What Is RM18?

RM18 is a fast-acting, non-selective herbicide designed to knock out weeds and grasses without messing up your soil for future planting. Its active ingredients are 18% glyphosate and a touch of diquat dibromide, which work together to zap weeds on contact.

I sprayed RM18 on a patch of crabgrass in my backyard, and within 12 hours, those pesky blades were wilting like they’d given up on life.

Key Features of RM18

• Fast-Acting: You’ll see weeds yellowing or browning within hours, with full death in 1-2 weeks.
• Soil-Friendly: It deactivates once it hits the soil, so you can replant in as little as 1-3 days.
• Rainfast in 30 Minutes: A quick shower won’t wash away your efforts.
• Targets Over 100 Weeds: From dandelions to kudzu, it handles a wide range of nuisances.
• Mix Rate: Typically 3-6 ounces per gallon of water, making it economical for spot treatments.

Pros of RM18

• Speedy Results: I love how fast RM18 works. When I treated a flower bed overrun with clover, I saw results by the next morning, which kept my project on track.
• Replanting Flexibility: Since it doesn’t linger in the soil, I could plant new flowers or grass seed a couple of days later without worrying about residual effects.
• Cost-Effective for Small Areas: At roughly $50-$60 per gallon, it’s cheaper than RM43 and stretches further for spot treatments.
• Easy to Apply: The lower mix rate means I can use a simple hand-held sprayer and not feel like I’m wasting product.
• Pet and People Safe After Drying: Once the spray dries, my dog can roam without issue, which is a big plus.

Cons of RM18

• Short-Term Control: RM18’s effects last up to 6 months, but I noticed new weeds popping up after a few months, especially in high-traffic areas.
• Non-Selective: It’ll kill anything green it touches, so I had to be super careful around my prized roses.
• Not Ideal for Large Areas: If you’re tackling a big space, the lower glyphosate concentration means you might need multiple applications.
• Environmental Concerns: Glyphosate has been linked to health and ecological issues, so I always wear gloves and a mask when spraying.

What Is RM43?

RM43 is the big gun of herbicides, designed for total vegetation control and long-term prevention.

With 43% glyphosate and 0.78% imazapyr, it not only kills existing weeds but also keeps new ones from sprouting for up to a year.

I used RM43 on my gravel driveway, and it’s been a weed-free zone for months—no small feat considering how stubborn those driveway weeds can be.

Key Features of RM43

• Long-Lasting: Prevents weed regrowth for up to 12 months, perfect for areas you want to keep bare.
• Dual Action: Works as both a pre-emergent and post-emergent herbicide, tackling seeds and grown plants.
• High Coverage: A 2.5-gallon jug can treat up to 43,243 square feet.
• Rainfast in 2 Hours: It sets quickly, though not as fast as RM18.
• Mix Rate: Requires 6-7.4 ounces per gallon, which is higher but covers more ground.

Pros of RM43

• Year-Long Control: After spraying my driveway, I didn’t see a single weed for nearly a year, saving me countless hours of maintenance.
• Versatile Applications: It’s perfect for fence lines, patios, and other areas where you want zero vegetation.
• Effective on Tough Weeds: It obliterated a patch of poison ivy that RM18 struggled with, thanks to the imazapyr boost.
• Large Area Coverage: The higher concentration means one jug goes a long way, making it cost-effective for big projects.
• Reliable in Harsh Conditions: Even after heavy rain a week later, the treated areas stayed weed-free.

Cons of RM43

• Soil Sterility: The imazapyr makes the soil off-limits for planting for up to a year, which was a hassle when I wanted to add a shrub nearby.
• Higher Cost: At $100-$110 per gallon, it’s pricier than RM18, and the higher mix rate adds up.
• Slower Results: It took about a week to see full effects, which tested my patience compared to RM18’s quick action.
• Drift Risk: Imazapyr can move through soil via water runoff, so I had to avoid spraying near my lawn to prevent accidental damage.
• Safety Precautions: The stronger formula requires strict adherence to safety guidelines, like wearing full PPE and avoiding windy days.

Comparing RM18 And RM43: My Real-World Experience

When I first tackled my weed problem, I used RM18 for a garden bed I wanted to replant with vegetables.

The speed was a game-changer—I sprayed in the morning, saw wilting by evening, and planted seeds a few days later.

The soil stayed fertile, and my tomatoes are thriving.

But when I tried RM18 on my gravel path, weeds started creeping back after a couple of months, which was frustrating.

Enter RM43. I used it on the same gravel path and around my fence line, where I wanted no growth at all.

It took longer to see results—about 10 days for the weeds to fully brown—but the area has stayed clear for nearly a year.

The downside? I couldn’t plant anything nearby, and I had to be extra careful not to let the spray drift onto my lawn.

When To Choose RM18?

RM18 is your pick if you’re planning to:

• Clear a garden bed or lawn for replanting.
• Tackle small, targeted areas with weeds like dandelions or clover.
• Work on a budget and need quick results.
• Avoid long-term soil impact.

I found RM18 perfect for my front yard, where I wanted to replace a weedy patch with new sod. The fast action and soil-friendly nature let me get the job done in a weekend.

When To Choose RM43?

RM43 is the better choice if you:

• Need to keep an area weed-free for a year, like driveways or patios.
• Are dealing with tough, persistent weeds like kudzu or poison ivy.
• Have a large area to treat and want long-term results.
• Don’t plan to plant anything in the treated area.

My driveway project was a success with RM43. I sprayed once, and it’s still bare ground months later, saving me from constant weeding.

Application Tips From My Trial End Error

Applying herbicides isn’t just point-and-spray—trust me, I learned the hard way. Here’s what worked for me:

• RM18: I mixed 4 ounces per gallon for spot treatments and used a pump sprayer for precision. Spraying on a sunny day around 10 a.m. ensured the weeds absorbed it quickly. I avoided windy days to prevent drift onto my lawn.
• RM43: I used 7 ounces per gallon for my driveway and made sure to check the weather—no rain for at least 2 hours. I wore full PPE (gloves, goggles, long sleeves) because of the imazapyr’s potency. I also marked treated areas with dye to avoid overlap.

Always read the label. RM18’s instructions are straightforward, but RM43’s higher concentration and soil residual effects demand extra caution. I once sprayed RM43 too close to a tree’s drip line and noticed some leaf yellowing—lesson learned.

Environmental And Safety Considerations

Both herbicides contain glyphosate, which has sparked debate about its impact on health and the environment.

I’m no scientist, but I take precautions.

Glyphosate can irritate skin and eyes, so I always wear protective gear.

RM18’s diquat dibromide adds a slight environmental risk, but it’s minimal since it deactivates in soil.

RM43’s imazapyr, however, can harm aquatic life if it runs off into water bodies, so I never spray near my pond.

I also consider the ecological footprint. RM18’s shorter residual effect feels less invasive, but RM43’s long-term soil impact makes me think twice about using it in sensitive areas.

If you’re eco-conscious, you might explore alternatives like vinegar-based herbicides, though they’re less effective for tough weeds.

• Cost Vs. Value: Which Gives You More Bang for Your Buck?

RM18 is cheaper upfront, with a gallon costing about $50-$60. For small projects, it’s a no-brainer—quick results and replanting flexibility make it worth every penny.

RM43, at $100-$110 per gallon, feels like a splurge, but its coverage and year-long control make it cost-effective for large, bare-ground projects. I calculated that RM43’s 2.5-gallon jug treated nearly three times the area of RM18’s, so it balances out if you’re covering a big space.

Which Should You Choose?

Your choice depends on your goal. If you’re like me and love a quick garden refresh, RM18 is your friend—fast, affordable, and soil-friendly. But if you’re fed up with relentless weeds in areas you want permanently clear, RM43’s long-lasting power is unmatched.

I keep both in my shed, using RM18 for garden prep and RM43 for my driveway and fence lines. It’s like choosing between a scalpel and a sledgehammer—pick the tool that fits the job.

Frequently Asked Questions (FAQ)

Conclusion: Make Your Yard Work For You

I’ve wrestled with weeds enough to know that choosing the right herbicide can save you time, money, and frustration. RM18 and RM43 are both powerful tools, but they shine in different scenarios.

If you’re planning a garden makeover, RM18’s quick action and soil safety will get you planting fast. If you need a weed-free zone for a year, RM43 is your go-to. Pick based on your project, and you’ll be on your way to a yard that makes you proud. What’s your next gardening challenge?

Let’s tackle it together!