What actually kills weeds for good

Most weedkillers just brown the tops off, so the weeds are back through your block paving a few weeks later. Here is what actually kills driveway, path and patio weeds down to the root, why the cheap sprays and home remedies keep letting you down, and how to stop them coming back.

The short version

Weeds only die for good when the root dies. That takes a systemic weedkiller, one the plant carries down into its own roots, applied properly and at full strength. Everything that only hits the top growth (pulling, burning, jet-washing, home remedies and most contact sprays) leaves the root alive in the joints, so the weed regrows. It is not about hitting them harder. It is about hitting the part that matters, then keeping the joints closed so new seed has nowhere to sit.

What works, and what just fills your weekend

A quick way to read it: if a method doesn't reach the root, whatever you saved in effort you pay back in a few weeks when it grows again.

Method	Kills root?	Lasts	The catch
Pulling or scraping	No	Weeks	Snaps the top off; the root stays and pushes up again, and you reopen the joints.
Hoeing	No	Weeks	Chops the visible growth only. The root is untouched.
Jet-washing	No	Weeks	Blasts off the greenery and washes out the jointing sand, so weeds seed back faster.
Boiling water	Rarely	Days	Scalds the top. Roots down in the sub-base usually survive it.
Salt, vinegar, bleach	Rarely	Varies	Knock the top back, but can wreck the soil, stain the paving and drift onto plants you want.
Flame / weed burner	No	Weeks	Scorches the leaves; the root barely notices.
Shop-shelf spray	Sometimes	Weeks	Often too weak or contact-only, so it browns the top and misses the deep roots.
Professional systemic spray	Yes	Months+	Carried down into the root, so the whole plant dies. Takes 2 to 4 weeks and needs dry weather.

Why they grow on your driveway in the first place

Weeds don’t grow out of the slab or the block. They root in the thin layer of grit, soil and debris that collects in the joints between your blocks and in the sub-base underneath. On most Leicester drives that means annual meadow grass, moss, chickweed and the tough perennials working their way down the sand-filled joints.

That is the whole problem in one sentence: the living bit you can see is sitting on top, but the part that keeps it alive is wedged down in a joint you can’t dig out. So the honest test for any method is simple. Does it get down into that root, or does it just deal with the green on top? Pull, hoe, flame or jet-wash and you deal with the green. It looks sorted for a fortnight, then it’s back.

Why nothing kills weeds “down to the root overnight”

It’s the most searched-for thing and it doesn’t exist. Anything that works overnight is a contact killer: it burns whatever it touches on the day and goes no further, which is exactly the top growth you don’t need to worry about. To kill the root, the weedkiller has to be taken in through the leaves and carried down through the plant, and that takes time.

So the wait is not the treatment failing. The wait is the treatment. You’ll usually see the weeds start to yellow within a few days, but it takes two to four weeks for the plant to carry it all the way down and die off properly, roots and all. If something browns them off by tomorrow morning, it hasn’t touched the root, and you’ll be doing it again next month.

Home remedies: do they work, and will they wreck your paving?

Boiling water, vinegar, salt and bleach all get passed around online. They share a problem (they only hit the top, so perennials regrow) and, on a hard surface, most of them bring a second problem: they damage the thing you’re trying to keep nice.

Vinegar is a contact burn. Household vinegar is too weak to do much, and even the strong stuff scorches the leaf without reaching the root. It can also corrode any metal it runs onto.
Salt does knock things back, but it sterilises the ground. Washed down into the sub-base it stops anything growing there for a long time and can’t be flushed out easily, which is the last thing you want next to borders or a lawn.
Bleach stains. It can permanently mark block paving, coloured concrete and natural stone like Indian sandstone, and it still doesn’t kill the root. Never mix it with vinegar either, that gives off chlorine gas.
Boiling water is the safe one for your paving, but it only scalds the top. The root down in the cool sub-base usually shrugs it off.

The straight verdict: for a stray weed in a crack, boiling water is harmless enough if you enjoy repeating it. For a whole drive or patio, salt and bleach risk your surface and the ground around it without ever settling the weeds. A proper systemic spray is the only one on that list that reaches the root without wrecking the paving.

Don’t scrape or jet-wash them off first

This is the one that catches most people out. The instinct is to blast the drive clean first, then treat it. It’s the wrong way round, and it makes the problem worse.

Jet-washing and scraping strip out the kiln-dried sand in the joints, chew up the block faces and open up the sub-base underneath. You’ve just cleared out the exact voids weeds love and brought buried seed up to the light, so the next flush comes through faster and thicker. Worse, you’ve torn off the leaves the weedkiller needs to get in through, so a spray afterwards has nothing to work on. Spray first, let it die off, then clean and re-sand once it’s dead.

Why some come back (and why that isn’t the same as it not working)

Here’s the honest bit no product label will tell you: nothing stops new weeds forever. Seed blows in on the wind and arrives in bird droppings all year round, so a month or two on you might see fresh green in the joints. That is brand-new seed germinating, not the weeds I treated coming back to life.

It matters because the two are different jobs. The weeds that were there and got sprayed should be dead and stay dead, and that’s what a guarantee covers. New seed settling in later is just what happens to any outdoor surface, and it’s managed with a bit of aftercare rather than another full treatment.

Keeping them from coming back

Once the weeds are dead and the joints are clear, the trick is to leave new seed nowhere to root. Refill the joints with kiln-dried or jointing sand so they’re packed tight rather than a soil-filled gap, and a paving sealant on top helps lock it in and slow the grit building back up. Sealing isn’t forever, it wants redoing every year or two, but it genuinely cuts down how much comes through.

That’s the difference between a drive that’s clear for a season and one that’s clear for years: kill the root properly, then close the joint so the next lot of seed has nothing to get into. The surface side of that, re-sanding and sealing block paving and sorting gravel, is in how to stop weeds in block paving and gravel.

Rather not spend your weekend on it?

I spray hard surfaces across Leicestershire and kill the weeds to the root, from £15. Send a photo of the weeds and your postcode and I’ll text you a fixed price within 24 hours. See weed spraying in Leicester for how it works.

Get my price

What doing it properly actually looks like

The weedkiller I use is professional-grade and systemic, and I’m qualified to use it. It’s taken in through the leaves and carried down into the roots, so the plant kills itself from the inside rather than just browning off on top. It’s rainfast fairly quickly, and once it reaches the soil it stops working, so it won’t linger in the ground or creep across to your borders.

If the whole drive is overgrown, the answer isn’t to strip it first, it’s to treat the lot and wait it out. Everything green takes the spray up, then dies back together over the next few weeks, and it gets cleared and re-sanded once it’s dead. It’s not instant, and anyone promising overnight results is guessing, but it’s the version that’s still clear months later. If you’d rather have it done than buy kit and repeat the job, that’s what I do.

About this resource

I’m The Weed Guy, a weed-spraying service for driveways, paths, patios and gravel across Leicestershire. This resource reflects how I treat hard-surface weeds day to day.

The honest disclosure: I make money when you book, so of course I’d rather do the job than watch you buy a sprayer. But the advice above is straight. You can absolutely do this yourself with the right systemic product, applied properly in dry weather, and a bit of patience. Most people call me because they’d sooner not, or they’ve already tried the cheap route twice and want it done once and done right.

Common questions

What kills weeds down to the root overnight?

Nothing does, and that’s worth knowing before you waste money. Anything that works overnight is a contact killer that only scorches the top. A systemic weedkiller reaches the root, but it needs two to four weeks to get there. The delay is the job working, not failing.

Is bleach or vinegar better for killing weeds?

Neither is a good idea on a driveway. Vinegar only top-burns and household strength barely does that. Bleach can permanently stain block paving and stone and still misses the root. Both leave the weeds to regrow, and bleach can wreck the look of your paving for good. Never mix the two, it releases chlorine gas.

Does salt kill weeds permanently, and will it ruin my driveway?

Salt knocks the top back but sterilises the ground. Washed into the sub-base it can stop anything growing for a long time and it’s very hard to flush out, so it risks your borders and lawn nearby. It’s not worth it on a surface you care about.

Should I jet-wash the weeds off first?

No. Jet-washing strips the jointing sand and opens up the sub-base, which is exactly where weeds root, so it tends to make the next flush worse. Spray first, let it die off, then clean and re-sand once the weeds are dead.

How do I sort a completely overgrown driveway?

Treat the whole lot in one go and wait for it to die back, rather than stripping it first. Everything green takes the spray up and dies off together over a few weeks, then it’s cleared and re-sanded. Send a photo and I’ll price it.

Is it safe once it’s dry?

Used correctly and left to dry, this class of weedkiller is low-risk on hard surfaces, and it stops working once it hits the soil rather than lingering. If you’d rather not handle it, that’s a fair reason to have it done by someone qualified to spray it.