The way you dig the hole has a big effect on how well a new tree or shrub establishes. The most common mistake is digging too deep and too narrow. This calculator sizes the hole from the root ball and gives the soil volumes.
Wide, not deep
Most tree roots grow in the top 12 to 18 in of soil and spread far beyond the canopy. Arborists and extension services recommend:
- Width: 2 to 3 times the root ball diameter. Loosened soil around the ball lets new roots spread quickly. Use 3 times in compacted or clay soil.
- Depth: no deeper than the root ball. The ball should sit on firm, undisturbed soil so it does not settle. The root flare, where the trunk widens at the base, must be at or slightly above the surrounding grade.
For an 18 in root ball that is 14 in tall: a hole 36 in wide and 14 in deep.
Soil volumes
hole volume = π × diameter² ÷ 4 × depth
The 36 × 14 in hole removes about 8.2 cubic feet of soil. The root ball takes about 2.1 cu ft, so about 6.2 cu ft goes back as backfill. A gently sloped, saucer-shaped hole is even better than straight sides; it uses a little less soil than the cylinder computed here.
Planting step by step
- Find the root flare: on many nursery trees, it is buried; remove soil from the top of the ball until you see it.
- Dig the hole and roughen the sides, especially in clay, so roots can escape.
- Remove the container, and for balled-and-burlapped trees, take off the wire basket and as much burlap and twine as possible once the tree is in place.
- Tease out or cut circling roots.
- Backfill with the native soil, without heavy amendments; roots that stay in rich backfill tend not to grow out.
- Water slowly to settle the soil and remove air pockets. The first soaking should at least wet the whole root ball; the calculator uses its volume as a guide, about 15 gallons here.
- Spread 2 to 4 in of mulch in a wide ring, keeping it a few inches from the trunk.
After planting
Water deeply once or twice a week through the first growing season, more in heat and sandy soil. Stake only if the tree cannot stand on its own, and remove stakes after a year. Call 811 before digging to locate buried utilities.