One is a loose, ready-to-use blend of wood fibre, composted bark, clay and sand; the other is a very dark material alive with fungi, worms and micro-organisms. Soil mix supports your plants from the day you plant them, while compost enriches the soil around them — together they make the perfect combination.
Soil mix designates a growing substrate that is ready for planting.
Soil mix is a blend of various mineral and organic matter, tailored to each type of plant.
Traditionally, soil mix counts a number of renewable raw materials such as:
Some non-renewable raw materials are also often included, such as peat.
Each item plays a part in preparing the best growing environment for the plant.
They will make it possible for
Both end up in the same pot or bed, but they are not interchangeable. Here is what each one is, what it is made of and what it actually does.
| What you are comparing | Soil mix | Compost |
|---|---|---|
| What it is | A growing substrate that is ready for planting | The result of recycling and breaking down organic matter, usually very dark in colour |
| What it is made of | A blend of mineral and organic matter: wood fibre, composted bark or RCW, clay, compost, soil conditioner, sand | Broken-down organic matter only |
| What it does for the plant | Lets air circulate, keeps a loose structure for roots, holds moisture and carries nutrients | Feeds the soil rather than acting as the growing medium itself |
| What it brings to the soil | A tailored blend adapted to the job or the plant, sometimes with organic fertiliser added | Live micro-organisms, mineral elements and humus |
| How long it works | Used as the growing medium from the moment of planting | Restructures and boosts soil ecosystems over a life cycle of 2 or 3 years |
In practice the two are partners: compost enriches the soil, soil mix supports the plant.
Raw material ratios and types can change depending on the type of expected garden work (sowing, planting, garden boxes, vegetable patch…) or the type of plant (orchids, cactus…).
Compost, on the other hand, results from the recycling and breaking down of organic matter.
More often than not of a very dark color.
Its main functions are to enrich the soil or soil mix with:
Over a life cycle of 2 or 3 years, it helps restructure and boost soil ecosystems, and thus increases plant growth.
In short:
Compost + Soil mix = the perfect combination for great plants!
Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Soil mix with compost for plants by Florentaise
