Does Boiling Water Kill Weeds? Experts Explain

Weeds, also known as plants out of place, are part of gardening. Tiny plants crop up in areas where you least expect them or alongside other plants, where they compete for the same resources. Some weeds are easy to remove while others require more time and effort. If you have an organic garden or want to minimize using herbicides and chemicals in your garden, you likely spend ample time pulling weeds. And you may wonder if pouring boiling water is an effective option to kill weeds naturally.

We spoke to gardening experts about how pouring boiling water over weeds works, when to use this method, and tips and considerations before implementing this technique. 

How Boiling Water Kills Weeds

Pouring boiling water on weeds is a chemical-free method that works as a contact herbicide to eliminate unwanted plants in an area of your garden. This technique is best for small weeds with shallow roots rather than weeds with deep roots or more established weeds. "[Boiling water] usually will only kill the top of the plant that's above ground and will not kill the root, especially on older weeds that have a deep root system or taproot," says Barbara Smith, Consumer Horticulturist with the Clemson Extension Home and Garden Information Center (HGIC).

The scalding water harms the foliage, not the roots, which is why it's best for small weeds. "Boiling water works by shocking the weeds, which damages the plant cells and ultimately kills them," says Carrie Spoonemore, co-creator of Park Seed's From Seed to Spoon app. "It is particularly effective on young, annual weeds and weeds growing in cracks or small areas."

Linda Vater, plant expert for Southern Living® Plant Collection, recommends this method for tiny weeds that may be cropping up along borders or crevices. "I regularly use this method in my garden for low-growing weeds that are difficult to pull out by the root or spread prolifically by seed, such as mazus reptans," she says.   

How Long Does It Take Boiling Water To Kill Weeds?

Weeds typically begin to die not long after boiling water is poured over the weeds. "The immediate effect of boiling water can be seen within a few hours to a day," says Spoonemore. Depending on the type of weed, you may need to pour boiling water several times before they die, she adds. 

The weeds will clue you in that the hot water is taking effect as they'll often change color from green to brown or look like they need water. "The weeds will often show signs of wilting and browning shortly after application," says Spoonemore. "However, the full impact may take a few days to be evident." 

Vater uses this method for specific areas in her garden. "If I have an area of weeds that are trying to establish, I’ll pour boiling water on them once a day or every other day or so until they turn brown," she says.  Once they're brown or dead, she'll apply mulch over the area. 

Factors To Consider

Using boiling water works for specific situations, such as borders, crevices, and small patches as well as tiny weeds with shallow root systems. "Boiling water is most effective for targeting small patches of weeds, not large areas," says Vater. You don't want to apply this method for a big area. It will take too long and you can harm the soil and neighboring plants.

If you have weeds mixed in with your flower patch or edible garden, you'll want to rethink this technique as you'll be putting all your plants in jeopardy. "It works well for weeds that are just beginning to establish, not those with extensive root systems or weeds that are intertwined with desirable plantings," says Vater. 

When considering this weed control option, make sure you won't be putting any plants, whether flowers, herbs, or shrubs in harm's way.  "Boiling water can harm surrounding plants and soil if they are within the splash zone or in direct contact with the hot water," says Spoonemore. The last thing you want is to accidentally harm or kill your plants in an attempt to get rid of weeds. "Boiling water can scald foliage or kill any plants it comes into contact with," says Vater. Spoonemore advises pouring boiling water slowly and carefully to avoid damaging nearby plants. 

Plus, you also want to consider the soil as scalding water negatively impacts all the important microorganisms that create a healthy ecosystem for your plants to thrive. "Repeated use of boiling water can potentially harm beneficial insects and soil organisms in the immediate vicinity," says Vater.

Tips For Using Boiling Water To Kill Weeds

• "Use a kettle with a narrow spout to help direct the water more precisely," says Spoonemore. 
• Make sure to pour the water as closely as possible to the weeds. "Aim the boiling water directly at the weeds to minimize the impact on surrounding plants," says Spoonemore.