Yes, a stump can be ground deeper than it needs to be, and past a point extra depth buys nothing but a bigger hole, more chips, more fill and more settling, plus more risk to buried lines and the roots of trees nearby. The right depth is set by what goes on the spot, and when a job needs more depth than a grinder can reach, the stump should be lifted out instead.
Deeper is not automatically better
It is natural to think that the deeper the grind, the better the job. Up to a point that is true: a stump ground well below grade is out of the mower's way and leaves room for soil on top. Past that point, every extra inch is more passes and more grindings, and it buys nothing for a lawn or a mulch bed. Grass needs a few inches of good soil over the wood. A bed needs a little more. A slab or a post needs the wood gone altogether, which grinding cannot do at any depth. So the useful question is how deep the spot needs it, not how deep the machine can go.
How deep a grinder can actually reach
Every grinder has a limit, set by the size of its cutting wheel and how far the arm can lower it. Manufacturers' published specifications for tracked stump grinders list maximum cutting depths below ground of roughly a foot to a foot and a half, depending on the model. Getting close to that limit is slow work, because the wheel is buried in its own chips and has to be cleared out pass by pass. Below the grinder's reach, the only way down is digging: an excavator or loader lifting the root ball out whole.
What a hole that is too deep costs you
A deep grind leaves a deep hole, and a deep hole has to be filled with something. Raked-back grindings fill it with wood that will rot and sink, so the dip comes back season after season. Filling it with soil means bringing in more soil than you would expect. Either way, a deep, wide hollow in a lawn takes longer to settle and level than a moderate one. On a slope, a deep hole can also collect water or wash out in heavy rain if it is left open or filled with loose chips. More depth means more of all of this.
Lines, rock and water
Depth also raises the odds of hitting something. Irrigation lines, lighting cable and invisible dog fence are usually shallow, so they are at risk at any depth, but deeper grinding reaches deeper things too, such as a water line or a drain pipe. Public lines are marked through 811 ahead of grinding, while private ones, which 811 leaves alone, have to be pointed out by the owner. Rock is the other limit. In mountain soils a grinder often meets stone below a stump, and the teeth do not cut rock. On low, wet ground, a deep hole may simply fill with water.
The roots of trees you are keeping
Grinding deep and wide near a tree you want to keep can do it real harm. Mississippi State University Extension notes that about 85 percent of a tree's roots are in the top 18 inches of soil, the same zone a deep stump grind works through. Where a stump sits close to another tree, grinding is often kept tight and moderate on that side to spare the neighbor's roots, even if that leaves a little old root in the ground. A tree that loses a big share of its roots can decline for years. Stump grinding near trees you want to keep goes into that in more detail.
When extra depth is the right call
There are good reasons to ask for more depth. Sod needs a firm soil bed over the wood. A planting bed needs room for real soil around new roots. A replacement shrub a little to one side of the old stump does better with the old wood well out of the way. And a stump in a spot that will be regraded may need to go deeper so the new grade covers it. In each case, say so before the quote, because depth changes the time and the amount of grindings. How deep does stump grinding go covers the standard depths.
When no grind is deep enough
If the plan is a footing, a slab, a post, a drain line or a pool, depth is the wrong tool. Any grind leaves roots spreading out below and beside the hollow, and they will rot and settle under whatever is built there. The same is true of a tree that blew over and left its root plate on edge. In those cases, the root ball comes out whole, the hole is backfilled and firmed, and the ground is left to settle. Full stump removal explains how that job runs and when it is worth the extra work.
Common Questions
What happens if a stump is ground too deep?
You get a bigger hole, more chips and more fill to deal with, and the spot keeps settling as the wood under it rots. Deep grinding also reaches more buried lines and more roots of nearby trees. For lawn or mulch there is no benefit past the standard depth.
Can a stump grinder go two feet below ground?
Not usually. Published specifications for tracked stump grinders put their maximum depth below ground at roughly a foot to a foot and a half. Anything deeper is a digging job: the root ball is lifted out with an excavator or loader and the hole is backfilled.
Does grinding a stump deeper stop the roots from sprouting?
Not by itself. Stump sprouts come from buds near ground level, and a standard grind below grade already removes those. Shoots that come up away from the stump come from lateral roots, which no grinding depth reaches. Those are dealt with by cutting or mowing them repeatedly.
What to Do Next
Say what the spot will become, lawn, bed, sod or something built, and the depth will be written into the quote in plain inches. Two pictures and the town are enough to start, and the number is (828) 574-4474.