Hardest vs easiest types of stumps to grind

What makes a stump hard to grind? There are three main factors that contribute to stump toughness:
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1. size
2. hardness (species and greenness)
3. access to the stump

As you’d expect, the sheer volume of the stump is going to be a big factor. It helps to think of this in terms of cubic volume: you’ve got surface area, and you’ve got depth.

Because stumps are roughly circular, a stump that’s only a couple inches wider increases the surface area (SA) significantly.

For instance, a stump that’s two feet in diameter has a SA of 452”.

A stump with a diameter of 2’-6”, though, has a SA of 706.86. That’s a difference of 254” square inches for a stump that seems only slightly bigger.

Then you factor in the depth: for every inch you go down, you have to multiply that surface area by 1. That’s why, in general, we recommend a conservative grind depth of 4-8”. This works for most situations, like planting grass or a garden over the grind site.

Hardness of the stump

What we refer to as “greenness” of the stump simply means how long the stump has been dead for. An older stump that’s well along in the decay process will be noticeably softer.

That’s why you should make good and certain your stumps are dead if you’re not going to get them removed immediately. Softening them up will save us time and save you money when it comes to grinding. You can see this article on five ways to make sure your stump is dead.

The other factor that determines hardness is the species itself.

Hardness by common species in the Snohomish area

What we refer to as “greenness” of the stump simply means how long the stump has been dead for. An older stump that’s well along in the decay process will be noticeably softer.

That’s why you should make good and certain your stumps are dead if you’re not going to get them removed immediately. Softening them up will save us time and save you money when it comes to grinding. You can see this article for five ways to make sure your stump is dead.

The other factor that determines hardness is the species itself.

Hardness by common species in the Snohomish area

The hardest woods you’re likely to ever come across are oak, mahogany, and hickory. The good news for homeowners in North America is that oak is the only one of the three that’s common on the continent. Here in Western Washington, the hardest woods you’re going to see a lot of are maple, oak, or walnut.

This list ranks common trees in the Puget Sound region from softest to hardest, according to the Janka scale:

1. Black cottonwood
2. Western Red cedar
3. Pine
4. Sitka
5. Western Hemlock
6. Alder
7. Douglas fir
8. Bigleaf maple
9. Black walnut
10. Oak

The most common hardwood in the Puget Sound region is probably the Bigleaf maple. In lowland areas like Snohomish County, you see them everywhere you look. Even though this is technically only middle-of-the-road hardness on the Janka scale, it’s one of the hardest trees in our area.

A notoriously hard tree that grows in our area is the Black walnut, sought after for it’s hardness and interesting aesthetics (this is probably the most valuable lumber tree in the area).

The cottonwood is both extremely common in the Puget Sound lowlands, and notoriously soft. Soft enough, in fact, to earn our rating of most dangerous tree.

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Whatever the hardness and size of your stump is, our SG-75 Bandit will make short work of it. To schedule an on-site estimate for your tree or stump removal, you can submit an estimate form.

Resources

Tree identification is made easy with the Snohomish Tree Western WA tree ID Guide.

See the hardness of North American species ranked in these two articles:

• https://handtoolessentials.com/blog/woodworking/lumber-guides/hardness-ratings-softwood-north-american-spieces/​
• https://thepatriotwoodworker.com/forums/topic/18738-the-hardest-wood-in-north-america/