| Scenario | Inputs | Typical recommended dig depth |
|---|---|---|
| Tree, container | Rootball height 25 cm, loam, good drainage | ~24 cm (plant slightly high) |
| Shrub, container | Rootball height 18 cm, clay, fair drainage | ~16 cm (raise for drainage) |
| Perennial division | Rootball height 12 cm, loam, good drainage | ~12 cm (near level planting) |
| Tulip bulb | Bulb height 5 cm, multiplier 2.5, loam | ~12 cm (to bulb top) |
| Daffodil bulb | Bulb height 6 cm, multiplier 3.0, sandy | ~19 cm (slightly deeper) |
- Rootball mode: total_raise = crown_raise + drainage_raise
- Rootball mode: raw_depth = (rootball_height − total_raise) + bedding_layer
- Bulb mode: base_depth = bulb_height × multiplier
- Bulb mode: adjusted_depth = base + soil_adjust + drainage_adjust + bedding_layer
- Both modes: dig_depth = depth × (1 − settling_factor/100)
- Select a method: rootball/container or bulb/corm.
- Choose units and keep all measurements consistent.
- Enter height and diameter, then set soil and drainage.
- Optional: add a small bedding layer and settling factor.
- Press Calculate to view depth above the form.
- Download your results as a CSV or PDF file.
Right-Sizing Depth for Root Health
Planting depth affects oxygen access, moisture balance, and long-term stability. A hole that is too deep encourages crown burial and slow decline, while a shallow hole can dry out quickly and expose roots. When digging, avoid glazing the side walls in clay; roughen them to prevent root circling and improve infiltration. Confirm grade using a straight board and tape often. This calculator estimates a practical dig depth using the rootball or bulb size, then adjusts for drainage, soil texture, and expected settling after watering.
Rootball and Container Planting Logic
For trees, shrubs, and perennials, the target is usually the root flare or crown sitting at, or slightly above, the finished soil grade. The calculator applies a “raise” value so the plant sits higher when drainage is poor. A thin bedding layer can level the base, but the bottom should be firm so the plant does not sink.
Bulb Depth and Rot Prevention
Bulbs and corms are commonly planted using a depth multiplier based on bulb height. Larger multipliers suit free-draining soils and colder climates, while heavy clay or wet beds benefit from slightly shallower planting. The calculator includes small soil and drainage adjustments to reduce rot risk while keeping bulbs insulated.
Soil, Settling, and Backfill Compaction
Newly dug soil settles after irrigation, especially when backfill is loose or sandy. The settling factor reduces the suggested dig depth so the plant finishes closer to grade after watering. After placing the plant, backfill in lifts and press gently to remove air pockets without over-compacting. Water once to lock in contact around roots.
Width, Watering Basin, and Mulch Placement
Depth is only half of the planting geometry. A wider hole makes it easier for roots to expand into loosened soil, which is why the calculator suggests a width multiple for woody plants. Shape a shallow watering basin outside the rootball edge. Keep mulch off stems and crowns, and measure depth from the finished soil surface, not the mulch.
FAQs
1) Should I include mulch thickness in the dig depth?
No. Measure from finished soil grade. Mulch sits on top and should not bury the crown or bulb top. Keep mulch pulled back from stems to prevent rot.
2) Why does the calculator reduce depth using a settling factor?
Backfill settles after watering, especially in loose soils. Reducing the dig depth helps the plant finish near grade instead of sinking below it.
3) What bedding layer works best under a plant?
Use a thin, firm leveling layer. Avoid a loose cushion that compresses later. A stable base prevents the rootball from dropping after irrigation.
4) How do I handle poor drainage sites?
Plant slightly higher, improve drainage, and avoid overwatering. Consider raised beds or soil amendment to increase air space and reduce standing water around roots.
5) What depth multiplier should I use for bulbs?
A common range is 2.0–3.0 times bulb height. Use lower values in wet clay and higher values in free-draining soil for better insulation and anchoring.
6) Does hole width matter if depth is correct?
Yes. Wider holes encourage lateral root growth and quicker establishment. For shrubs and trees, aim for a wider zone of loosened soil than the rootball itself.