Finished growing-medium depth is not the same as new soil
A guideline for total growing-medium depth describes the finished layer after the site has been prepared. It does not automatically mean that the same amount of new soil must be delivered. Existing soil may sometimes remain or be mixed in if it suits the plants, drainage and project.
Keep two decisions separate: how deep the finished growing medium should be, and how much of that volume actually needs to be added or replaced.
Directional depths for different uses
Follow the needs of the plant, soil product and site. As directional figures, Kekkilä gives about 20 cm for lawns, 40–60 cm for perennials and shrubs, and 60–80 cm for trees. Groundcover perennials may need around 20–30 cm. These values describe the finished growing medium, not a universal order quantity.
- Lawns: about 20 cm as a directional figure.
- Perennials: often 40–60 cm.
- Shrubs: often 40–60 cm.
- Trees: often 60–80 cm.
- Groundcover plants: often around 20–30 cm depending on the plant.
Plant choice, root ball, existing soil and water flow can change what works on the site.
Estimate how much new growing medium is needed
First decide whether existing soil will stay, be mixed in or be removed. Then calculate the area that will actually be filled and the new layer depth needed. Do not automatically fill the entire planned depth with purchased soil. Check the root collar, finished level and water flow as well.
Example: finished layer and added quantity
If a 24 m² area needs a finished growing medium depth of 20 cm, its geometric volume is 24 m² × 0.20 m = 4.8 m³, or 4,800 litres. If 8 cm of suitable existing soil can stay, the added depth is 12 cm:
24 m² × 0.20 m = 4.8 m³
24 m² × 0.12 m = 2.88 m³
4.8 m³ describes the finished total growing medium. 2.88 m³ is the geometric volume of new material added in this example. The supplier's product, settling and ordering unit can affect the practical order quantity.
In Maavio you can record the new layer depth for the area and keep the added-material calculation separate from the total finished depth.
Planting holes, subsoil and water flow
A deeper growing medium does not automatically solve compacted subsoil or standing water. Check soil structure, falls and drainage before ordering material. For trees, a broad and functioning root zone is more useful than a narrow deep hole that holds water.
Checks before ordering soil
- Which plant or use is the area intended for?
- Which product and finished growing-medium depth suit the site?
- Does the measured area actually correspond to the area being filled?
- Will existing soil stay, be mixed in or be removed?
- How will water flow, and what finished level is needed?
- What order quantity and settling guidance does the supplier give?
Plan your garden project with Maavio
Maavio is a garden-planning app that keeps areas, material layers and quantity calculations together. Build a shopping list from your materials and follow the project’s progress in the same plan, from planning to implementation.
Available on Google Play
iOS version coming later in 2026.