Does Boiling Hot Water Kill Weeds?

Does Boiling Water Kill Weeds?

Sort of, but not really. Boiling water will scald and damage weeds on contact, and it might finish off very young seedlings. But for established weeds with any kind of root system, it’s more of a temporary setback than a permanent solution.

The internet loves this method because it’s free, completely natural, and there’s a satisfying sizzle when you pour it on. We get it. But after testing it ourselves, we can confirm what experienced gardeners already know – it’s one of the least effective homemade weed killer methods out there.

That said, it’s also one of the safest for the environment, so let’s look at when it might actually be worth trying and when you’re better off with something else.

How Does Boiling Water Affect Weeds?

Boiling water kills plant cells through thermal shock. When water at 100 degrees Celsius contacts plant tissue, it ruptures cell walls and denatures proteins almost instantly. The affected parts of the plant turn brown and wilt, often within hours.

The problem is that boiling water only damages what it directly contacts. By the time it’s soaked into the soil and reached the roots, it’s cooled down significantly. The root system – where perennial weeds store their energy for regrowth – typically survives completely unharmed.

This is why boiling water works on tiny seedlings (minimal root system) but fails against established weeds. Deep-rooted perennials like brambles, ivy, nettles, and bamboo will simply regrow from their intact root systems within a few weeks.

Our Boiling Water Test

We tested the boiling water method on weeds growing between paving slabs – a typical use case. We used five full kettles of boiling water to treat a relatively small area.

Within 24-48 hours, the treated weeds looked thoroughly scorched. Brown, wilted, and apparently dead. If we’d stopped checking at that point, we might have declared success.

But we kept watching. Within two to three weeks, fresh green shoots were emerging from the base of most of the “dead” weeds. The roots had survived, and the plants were regenerating. Five kettles of effort, and we were essentially back to square one.

Compare this to a proper strong weed killer that travels through the plant to kill weeds permanently, roots and all, from a single application.

The Effort Problem

Even if boiling water worked perfectly, there’s a practical issue: it’s incredibly labour-intensive.

A standard kettle holds about 1.7 litres. To treat even a small patio, you’re looking at multiple trips back and forth to the kitchen, waiting for the kettle to boil each time. For a driveway or larger area, you’d need dozens of kettles – and the water cools rapidly as you work, becoming less effective with each passing second.

Then there’s the regrowth issue. Because the roots survive, you’ll need to repeat this process every few weeks throughout the growing season. That’s a lot of kettles, a lot of time, and a lot of electricity for results that never actually stick.

Safety Considerations

Boiling water is environmentally safe – it leaves no chemical residue and won’t harm soil health. But it’s not without risks to you personally.

Scalding water can cause serious burns. Splashback from uneven paving, tripping while carrying a full kettle, or steam burns are all real possibilities. Keep children and pets well away from the area, and take your time – rushing increases the risk of accidents.

Never use boiling water on your lawn unless you want to kill your grass along with the weeds. And avoid using it on artificial grass – many synthetic turfs are plastic-based and can melt or deform from the heat.

When Boiling Water Might Work

Despite its limitations, boiling water isn’t completely useless. It can work on very young seedlings that have germinated in paving cracks – catch them in the first week or two before they develop proper root systems. It’s also useful as a quick cosmetic fix when you need weeds to look dead for a few days, even if they’ll recover later.

For small-scale spot treatment on patios or block paving, combined with regular maintenance, it can form part of an ongoing weed management routine. Just don’t expect one treatment to solve the problem permanently.

Better Alternatives

If you’re committed to DIY methods, vinegar and salt are slightly more effective contact killers, though they share the same fundamental limitation of not reaching roots. Bleach is stronger still, but comes with environmental concerns and can damage surfaces.

For driveways and gravel areas where you want long-term results, a long-lasting weed killer will save you time and frustration. These products contain systemic ingredients that travel through the entire plant, killing roots completely so weeds don’t return.

For a full comparison of all the DIY options and their effectiveness, see our complete guide to homemade weed killers. We’ve tested them all so you don’t have to.