When you remove a tree, a substantial root structure remains under the ground because of the extensive spreading of root masses. Underground tree stumps cause physical problems on your property, because they can prevent you from planting and growing other plants in certain areas. There are various methods to get rid of underground tree stumps. One of the easiest is to accelerate decomposition with chemicals. Stump remover products are available from nurseries and garden centers for as little as $5 and contain nitric acid, potassium nitrate or saltpeter and sulphuric acid.
Drill through dirt or mud, if necessary, to make vertical holes in the top of each underground tree stump. Use a one-inch drill bit to drill approximately one foot deep, so that the chemical can reach the inside of the stump.
Make diagonal holes at a 45-degree angle if the top of the stump is at ground level and you can get to the top sides of the stump. This may require the scraping or digging of some of the soil around the stump, to gain better access.
Pour chemical stump killer into each hole. Follow the manufacturer's application instructions. Usually four ounces in each hole is recommended. Add water to each one to completely fill to the surface level.
Evaluate the stumps weekly. It will take several weeks for the chemicals to begin breaking down underground tree stumps. The wood will begin to soften and crumble.
Break apart the underground tree stumps once they get soft enough. Use a shovel or axe to lift up pieces of the stumps, and discard them.
Add more of the chemical stump removal product if some sections of the underground tree stumps are stubborn. If the root system was extensive, one application may not be enough to completely break up a stump. Drill new holes in the remaining portions of the stump, and reapply the stump killer.
Fill the holes in the ground left behind with soil, and restore the grass or sod. It's common for the area to depress slightly over time, so mound the soil slightly to allow for this.