How to kill tree roots – in backyards and pipework

There are many good reasons to kill tree roots – this is what the experts suggest as the best and fastest ways to do so

Tree roots
(Image credit: Getty Images)

If you want to know how to kill tree roots, it's likely that you are having problems with them invading pipework, emerging from under patios and lawns, or even causing problems with foundations. 

Or perhaps you need to remove an unhealthy tree, know how to remove a tree stump, but also know that this doesn't stop the roots growing? In which case, you will want to ensure the roots don't continue to cause problems and will need to remove as much of them as is possible.

'Always take care when trying to kill or remove tree roots. If you want to cut up the root system to kill it, be aware that it could be wrapped around underground pipes or cables,' says Fiona Jenkins, gardening expert at MyJobQuote. 'Should you be in any doubt or suspect that the root system is well established, hire a reputable gardener to tackle it for you. This will save you time and effort and prevent accidental damage.'

It goes without saying of course that, for many, killing tree roots will need the services of a professional. But if your tree root problem looks manageable, this is how to tackle the job.

How to kill tree roots

Killing invasive tree roots – along with tree removal and controlling tree root growth generally – should save you both inconvenience, property damage and expense in the long run. 

Prevention is better than cure, so as you plant your garden, ensuring the trees you put in are of a suitable size and have a root barrier around the roots will save you having to deal with this problem in future. 

But if you've inherited a tree with a house, mistakenly planted one with invasive roots or put one too near to the house, or a tree has become diseased and dangerous, you will need to deal with the problem, and learn how to kill tree roots. 

How to kill tree roots with boiling water

To kill tree roots with boiling water, expose as much of them – and the stump if it's still intact – and drill holes into them. Then simply pour boiling water into the holes. The heat will shock the roots, damaging and hopefully kill it. 

How to kill tree roots with rock salt

Gena Lorainne, a gardening and landscaping expert at Fantastic Services suggests killing tree roots with rock salt.

'Dig several four inch holes into the cut surface of the tree trunk. Additionally, you can also drill some holes in the exposed roots (if present),' she says. 'Fill the holes with rock salt and pour water into them so the holes are filled to the top. 

'A very important thing to remember is to avoid overfilling and spilling, as rock salt is toxic to other vegetation and pets. You will have to repeat this process several times for a couple of months and eventually, the salt will do its job and kill the tree roots. You will know that the job is done If there isn’t any regrowth from the trunk.'

Tristan Sissons, Garden Buying Manager at Homebase suggests sealing the holes drilled after the rock salt has been poured in with candlewax. 'This stops the salt from getting blown around the garden and harming other plants,' he says. 'Cover the tree stump with a plastic sheet or tarpaulin. Check on it every couple of weeks – when it’s dead, it will break up easily.'

How to kill tree roots with herbicides

Gena Lorainne suggests that herbicides can be a good way to kill tree roots. 

'You will need a small bucket, a garden sprayer or paint brush, a garden hose or watering can, and a glyphosate herbicide (with at least 40% active ingredient concentration),' she says.

'Using the saw, make a cut across the trunk if the tree was cut down more than a few days ago. The purpose of the cut is to expose new flesh. If the tree is three inches or less in diameter, make a cut across the entire surface of the trunk. When it comes to bigger trees, you should cut and expose new flesh of the outer 2 to 3 inches. 

'Saturate the cambium layer of the tree with 2 to 3 inches of water (this is the outer ring which is located just under the bark). As this layer is still alive, the liquid will help transport the herbicide from the live tissue directly into the tree roots.

'Create a concoction with water and glyphosate herbicide (in a 50/50 ratio) and apply the solution to the exposed cambium layer. You can use a hand-held sprayer, garden sprayer or a paint brush to apply the concoction. Just be careful of the surrounding grass and plants when working with the solution, as it’s highly toxic for other vegetation too. You should be able to see visible results in about a couple of weeks.' 

How to kill tree roots in pipes

A natural way to kill tree root in pipes is with a combination of baking soda, vinegar, salt and boiling hot water. Flushed when hot down the lowest toilet in your home – perhaps the powder room's – will allow the salt to reach the roots there. This won't happen with the first flush, you will need to repeat the process. 

Which trees have the most invasive roots?

Just as with invasive plants, which can cause damage to masonry, fences and other plants, there are some trees you will want to avoid planting because of their invasive roots. These tend to be trees with surface feeder roots, which can grow quite large and cause problems. They include: 

  • Conifers
  • Willow
  • Oak
  • Silver maple
  • Japanese knotweed
  • Southern magnolia
  • Sycamore
  • Japanese fir 
  • Acacia
  • Hybrid poplar
  • Vine maples

Why do tree roots invade pipework?

A tree's roots are driven to look for water and nutrients, so it's a given that they will gravitate towards pipework underground, especially if there are the tiniest of leaks coming from them. Tree roots can invade even the smallest of gaps, causing wider damage, so should be dealt with as soon as they are discovered.

Lucy Searle
Lucy Searle

Lucy Searle has written about interiors, property and gardens since 1990, working her way around the interiors departments of women's magazines before switching to interiors-only titles in the mid-nineties. She was Associate Editor on Ideal Home, and Launch Editor of 4Homes magazine, before moving into digital in 2007, launching Channel 4's flagship website, Channel4.com/4homes. In 2018, Lucy took on the role of Global Editor in Chief for Realhomes.com, taking the site from a small magazine add-on to a global success. She was asked to repeat that success at Homes & Gardens, where she has also taken on the editorship of the magazine.