How you dig the hole decides how well a tree or shrub establishes. The common mistake is a deep, narrow hole, which makes the plant sink and holds water around the trunk. This tree planting hole size calculator gives you a hole that is wide enough for roots to spread and shallow enough to keep the root flare where it belongs.
How to use the tree planting hole size calculator
- Measure the root ball diameter in inches, across the widest part. For a container plant, measure the soil mass or the pot top.
- Measure the root ball height from the bottom to the top of the soil, or to the root flare if the soil sits above it.
- Read the width range and depth. The calculator also shows how much soil you will dig out.
The math behind it
Hole width = 2 to 3 × root ball diameter
Hole depth = root ball height − 1 in
Worked example: a 15 gallon container tree
The root ball is 18 inches across and 16 inches tall. The hole should be 36 to 54 inches wide and 15 inches deep. Digging at the wider size removes about 20 cubic feet of soil.
Worked example: a small shrub
A shrub in a 10 inch wide, 9 inch tall pot needs a hole 20 to 30 inches wide and 8 inches deep.
Why wide, not deep
Most tree roots grow outward in the top foot or so of soil. A wide hole of loosened soil gives roots an easy path, and the original soil underneath stays firm so the tree does not settle. A deeper hole, filled with loose soil, can sink as the soil compacts and bury the trunk.
Find the root flare
The root flare is where the trunk widens as it meets the roots. It should sit at or just above the soil surface. Nursery trees are often planted too deep in their pots or burlap, so brush away extra soil at the top until you find it, and measure from there.
Planting steps
- Dig the hole to the width and depth above, with sloping sides, and roughen the walls so roots can pass through.
- Set the tree on undisturbed soil, so it sits slightly high rather than low.
- Remove wire, rope, tags and any container, and cut circling roots.
- Backfill with the soil you dug out, firming lightly, and water well.
- Mulch 2 to 4 inches deep in a wide ring, keeping it away from the trunk. Use our mulch calculator to size the ring.
Amend the soil only if it is extremely poor, and use the soil calculator if you are filling a raised or built-up area. For several shrubs, see the hedge plant count calculator.
Frequently asked questions
How wide should I dig a tree planting hole?
Two to three times as wide as the root ball. The wider, the better, as long as the depth stays no deeper than the root ball.
How deep should I plant a tree?
No deeper than the root ball, with the root flare at or slightly above the surrounding soil. Planting too deep is a leading cause of poor tree health.
Should I add compost or fertilizer to the hole?
Usually not. Backfill with the native soil, because roots grow better when the planting hole matches the surrounding soil. Mulch on top is the better investment.
When is the best time to plant a tree?
Fall and early spring, when the weather is cool and roots can establish before summer heat. Check your frost dates with our frost dates by ZIP code tool.