Stump remover chemicals: does potassium nitrate or Epsom salt actually work?

What stump remover chemicals are, and what each one does

A stump remover is not a stump killer. Products sold as removers speed the breakdown of dead wood or soften it for chopping out; products sold as stump killers are herbicides for a fresh cut on a living tree. If you simply want the stump gone this season, stump grinding in Washington and Oregon does it in one visit, and the rest of this page is for the do-it-yourself route.

Lowe’s says commercial stump removers typically contain potassium nitrate, which it says encourages microbial activity. Bonide’s Stump-Out uses a different chemical, sodium metabisulfite, and its label says the treatment leaves seasoned wood porous enough to chop out with a hatchet or axe. Here is what each common option is, and what its maker or an independent source says about it.

Sources: Lowe’s stump guide; Bonide Stump-Out and Stump & Vine Killer product pages and labels; WSU Puyallup, Epsom salts; Pacific Northwest Extension, PNW 601; WAC 173-425-030 and -040; PubChem, potassium nitrate; checked 2026-10-02.

How to use a potassium nitrate stump remover

The directions Lowe’s and Bonide give follow the same pattern: drill holes, add the product and water, wait. The drawing redraws the pattern on Bonide’s Stump-Out label. Use your own product’s label for the amount that goes in each hole; it varies by product, and this page does not repeat it.

1. Make sure the stump is dead and seasonedBonide’s label says green, freshly cut stumps should season at least one year, or 18 months for a large stump, and its product page says it works best on stumps cut 18 months or longer.
2. Drill the holesOne-inch holes straight down from the top, about 10 inches deep on Bonide’s label; Lowe’s says 8 to 12 inches.
3. Drill the side holesOn the side of the stump, 4 to 5 inches below the top, drill 1-inch holes slanting downward, per Bonide’s label.
4. Add the product and waterIn the order and amount your label gives. Bonide’s says granules first, then fill the holes with water; Lowe’s notes that many products have you fill the holes with water first.
5. Keep the wood wetLowe’s chemical method: water the stump and the soil around it, then cover it with a tarp held down with mulch.
6. Wait, then chopBonide says 4 to 6 weeks; then break out the softened wood with a hatchet or axe. Lowe’s says chemical removal can take several months or longer.

How long does stump remover take in the Northwest?

Longer than the box suggests, because the clock starts when the tree comes down, not when the granules go in. Bonide’s own steps add up to about 13 months for a small fresh stump (at least a year of seasoning plus 4 to 6 weeks) and about 19 months for a large one, before any chopping. Left alone, Lowe’s puts natural decay at 3 to 15 years.

Moisture is the variable you control. The Forest Service’s Wood Handbook says serious decay happens only when wood is wetter than its fiber saturation point, about 30 percent moisture, and that wood kept air dry does not decay at all. Decay is also slow below 50°F, and the fungi do best around 77°F. A stump that dries out in summer can stall, which is why the directions call for water and a tarp.

Portland gets 82 percent of its 36.92 inches a year from October through April, and only 1.05 inches in July and August combined. East of the Cascades the whole year is short of water: Spokane averages 16.45 inches, Bend 10.62 and Yakima 8.01, by the same NOAA normals. A hose and a tarp through the dry months keep a treated stump wet enough to keep decaying.

Waiting has a cost too: a year or more of mowing around the stump, then the chopping. The site’s model puts grinding at $4–$6 per inch of diameter with a $150 minimum per visit, which covers any stump up to 24 inches (modeled estimate, not quotes; method). Sizes and add-ons are on stump grinding cost, and the rent-or-hire math for a long list of stumps is in stump grinder rental.

Does Epsom salt work for stump removal?

Epsom salt is magnesium sulfate, and we found no extension service or university source that recommends it for removing stumps. Linda Chalker-Scott’s review of Epsom salt claims for WSU Puyallup covers the garden uses people make of it and does not mention stumps at all. Its warning applies anyway: soluble nutrients applied beyond what plants need “end up somewhere else,” often as a pollutant, so she advises adding magnesium only where a soil test shows a shortage.

Rock salt has a known cost to the yard around the stump. The Pacific Northwest extension bulletin on salt-affected soils (PNW 601, published through Oregon State University Extension) explains that salts in the root zone make it hard for roots to pull water from the soil, and that excess sodium breaks down soil structure, plugging pores and slowing drainage. The stump’s roots are dead; the lawn, beds and trees rooted in the same soil are not.

Stump killer vs stump remover: what neither one does

A stump remover will not kill a living stump or stop it sprouting; Bonide tells you to let a green stump season first. If the tree is a bigleaf maple, laurel or cottonwood, all of which come back from the stump or roots, the tool is a cut-stump herbicide applied when the tree is cut: the Pacific Northwest Weed Management Handbook says stump treatments go on right after cutting, in any season, in a narrow band around the living layer just inside the bark.

Bonide’s Stump & Vine Killer shows what a stump killer is: its label lists triclopyr at 8.8 percent and directs it onto the freshly cut surface to kill the stump and prevent sprouting. The same label warns against letting it reach storm drains, ditches, gutters or surface water and says to keep people and pets out of the area during application. For glyphosate and imazapyr, the handbook adds a caution: they can move through root grafts and injure nearby plants of the same species.

Product choice, Northwest species and work near water are covered in how to kill a tree stump. Shoots coming up from roots away from the stump are a separate problem, covered in how to remove tree roots, and the full comparison of digging, grinding and rotting is in how to remove a tree stump.

The “then burn it” step, and safety

Bonide’s Stump-Out label ends with fire: after 4 to 6 weeks, fill the holes with kerosene or fuel oil and light it, or burn charcoal briquettes on top. The label says treated stumps burn without open flame or billowing smoke, so the product “may still be used” where open burning is prohibited. We would not treat a product label as a burn permit.

Washington’s rule defines outdoor burning as combustion of material of any type in an open fire or outdoor container without control of the combustion or its emissions (WAC 173-425-030), and residential burning has been banned in urban growth areas and cities over 10,000 people since the end of 2000 (WAC 173-425-040). Oregon DEQ says restrictions depend on where you live, with cities, counties and fire districts adding their own. Check Washington yard debris burning rules or Oregon yard debris burning rules, and ask your clean air agency or fire district before lighting a stump. Not legal advice.

Safety: Potassium nitrate is classed “May intensify fire; oxidizer” in PubChem’s summary of company hazard notifications. The International Chemical Safety Card says it is not combustible but enhances the burning of other substances and should be stored separated from combustibles, and the federal Emergency Response Guidebook entry PubChem cites warns this class of oxidizer can ignite wood, paper, oil and clothing. Store it away from fuel cans and keep fire off a treated stump.