What chemicals remove tree stumps?

Four products dominate UK tree stump chemical removal: SBK Brushwood Killer (triclopyr, glyphosate-free), Roundup Tree Stump Killer (glyphosate-based), potassium nitrate, and ammonium sulphate. SBK and Roundup are systemic herbicides that kill living tissue; potassium nitrate and ammonium sulphate are nitrogen-rich salts that accelerate fungal decay of an already-dead stump.

Two different jobs, two different chemistries. Herbicides kill the living cambium layer so a freshly cut stump cannot regrow. Salts feed the fungi that rot already-dead wood. Using a salt on a living stump achieves nothing; using a herbicide on a stump felled five years ago is equally pointless. Pick the product by what stage the stump is at.

SBK Brushwood Killer (triclopyr, glyphosate-free)

SBK Brushwood Killer is a triclopyr-based selective herbicide sold by Vitax in 250ml and 1L bottles for £12 to £22. It is glyphosate-free — relevant if you want to avoid glyphosate for organic-garden or ethical reasons. Triclopyr targets the auxin pathway in broadleaf woody plants and is harmless to grasses, which makes it a good fit for stumps in lawns.

Mode of action: applied neat or 1:24 with paraffin onto a freshly cut stump or into drilled holes, the triclopyr is absorbed by the cambium and translocated through the root system, killing the entire stump and root crown within 4 to 6 weeks. The wood itself then needs 6 to 9 months of weathering to soften enough to break up.

Roundup Tree Stump Killer (glyphosate-based)

Roundup Tree Stump Killer is the home-user concentrate version of glyphosate, sold in 250ml bottles for £8 to £15. Glyphosate inhibits the EPSPS enzyme in the shikimate pathway, blocking protein synthesis. It is non-selective — it kills everything green it touches, including grasses, which makes accidental spills more costly than with SBK.

Apply within 24 hours of felling. Drill 8 to 12 holes 25mm wide by 100mm deep into the freshly cut surface, fill each hole with neat concentrate, and cover with plastic sheeting. Expect visible foliage death on any remaining sprouts within 7 to 14 days, full stump kill in 4 to 6 weeks, and a rotted, breakable stump in 8 to 12 months.

Potassium nitrate (saltpetre)

Potassium nitrate, also sold as Stump Out or saltpetre, is a 99% pure KNO3 powder costing £8 to £20 for a 500g pack. It is not a herbicide — it cannot kill a living stump. It is a fungal accelerant: drilled into a dead, dry stump and watered in, the nitrogen feeds the white-rot fungi that break down lignin and cellulose.

Application: drill 8 to 12 holes 25mm wide by 200mm deep, pour in a level tablespoon of potassium nitrate per hole, top up with hot water, then cover. Re-water monthly. After 6 to 12 months in warm, damp weather the stump should be soft enough to chop out with a mattock. Cold winter applications can stall for the entire season.

Ammonium sulphate

Ammonium sulphate is a high-nitrogen agricultural fertiliser ((NH4)2SO4) costing £6 to £12 for a 1kg bag. Like potassium nitrate it accelerates rot rather than killing the stump, but it works faster on softwoods and acidifies the soil around the stump — useful for ericaceous beds, problematic near limestone paths or alkaline-loving plants.

Same drilling pattern as potassium nitrate (25mm holes, 200mm deep) but use 2 tablespoons per hole because ammonium sulphate is less concentrated in nitrogen by weight. Soften visible in 4 to 6 months on softwood stumps, 8 to 12 months on hardwood. Watch for yellowing on neighbouring acid-sensitive plants within a 2-metre radius.

How long does chemical removal take?

Tree stump chemical removal takes 3 to 12 months from application to a soft, breakable stump. SBK and Roundup kill the stump in 4 to 6 weeks but the dead wood still needs 6 to 9 months to rot. Potassium nitrate and ammonium sulphate need 6 to 12 months of warm, damp weather to soften the wood enough to chop out.

Two factors decide which end of the range you land on: wood density and weather. Soft pines, birch, and willow rot inside 4 to 6 months. Hardwoods — oak, beech, yew, sweet chestnut — sit at 9 to 12 months minimum, and a cold, dry winter can pause progress entirely. Compare this with professional grinding, which finishes the job in 15 to 90 minutes for £85 to £300, the same week you call.

Timeline by product and wood type

Is it safe to use stump killer at home?

Chemical stump killers are legal for UK domestic use but the RHS does not recommend them in domestic gardens. Risks include soil contamination, harm to nearby plants via root grafts, pet poisoning, and groundwater leaching. Always wear nitrile gloves and eye protection, drill holes 25mm deep, fill, then cover with plastic and a brick.

The Royal Horticultural Society's published guidance on stump removal explicitly favours mechanical methods for the home gardener and notes that chemical control is "rarely justified" outside commercial forestry or invasive-species control. The concern is not just user safety — it is the off-target damage to soil microbiota, earthworms, and nearby trees connected via mycorrhizal networks.

Application method, step by step

Whether you use SBK, Roundup, potassium nitrate or ammonium sulphate, the mechanical steps are nearly identical. Get this right and you give the chemical its best chance of working.

1. Cut the stump as low and level as possible — ideally within 24 hours of treatment for herbicides.
2. Drill 8 to 12 holes 25mm wide. Depth: 100mm for herbicides, 200mm for salts. Angle the outer holes inward at 45 degrees.
3. Fill each hole. Neat herbicide for SBK or Roundup; one level tablespoon of potassium nitrate or two of ammonium sulphate.
4. For salts only, top up with hot water to dissolve the granules into the wood.
5. Cover the stump with thick black plastic sheeting and weight with bricks. The cover keeps rain from washing the chemical out and traps moisture for fungi.
6. Check monthly. Re-water salts. Re-treat herbicides if green shoots appear after 8 weeks.

PPE is non-negotiable: nitrile gloves, eye protection, long sleeves, and closed shoes. Keep children and pets off the area until the cover is in place. If you would rather skip the year-long wait and the chemicals, hiring a grinder yourself is a same-day alternative — though most homeowners find the £85 to £300 professional fee cheaper than the day-rate hire plus PPE plus fuel.

Why does grinding beat chemicals?

Stump grinding finishes the job in 15 to 90 minutes; chemical removal takes 3 to 12 months and still leaves a dead stump to dig out. Grinding costs £85 to £300 versus £10 to £40 for chemicals, but grinding produces a plantable surface the same day with no soil residue and no waiting.

The honest case for chemicals is narrow. They make sense if access blocks a grinder entirely — a stump behind a locked side gate the machine cannot fit through, or one on a steep bank where wheeled equipment is unsafe. For a full method comparison of grinding versus chemical and excavation, the gap widens further when you factor in soil quality, replanting timing, and the visible dead-stump eyesore that chemicals leave for the better part of a year.

Chemicals also fail more often than the packaging suggests. Application more than 24 hours after felling, cold-weather starts, dense hardwoods, and rain washing the product out of the holes can all stall a treatment indefinitely. If a 6-month application shows no softening, you are back to square one and out the cost of the product plus the year of waiting. Sibling page tree stump killer UK covers the full chemical-method overview if you want to weigh both sides before committing.

The bottom line

If you have a small softwood stump, no access constraints, and a year to wait, chemicals are the cheapest route. For everything else — hardwoods, multiple stumps, hedge clearances, sales of houses, or simply a garden you want to use this season — grinding is the faster, cleaner, and ultimately cheaper choice.