Soil mix or compost, what is the difference?

Even though these two products are often confused, they do have very distinct uses and very different results.

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:

  • wood fiber (Hortifibre is a pioneer in this respect)
  • composted bark shards or RCW mulch
  • clay
  • compost (actually one of the components of soil mix)
  • soil conditioner
  • sand

Some non-renewable raw materials are also often included, such as peat.

  • It’s best to find soil mix that doesn’t include these non-renewables, though.

Each item plays a part in preparing the best growing environment for the plant.

They will make it possible for

  • air to circulate in the soil mix
  • roots to develop easily thanks to loose structure
  • moisture to be retained and leached to the plants
  • nutrients to be brought to the roots…

Differences between compost and soil mix

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:

  • live micro-organisms (fungi, thrips, worms…)
  • mineral elements
  • humus

Over a life cycle of 2 or 3 years, it helps restructure and boost soil ecosystems, and thus increases plant growth.

In short:

  • Soil mix is a complex blend that supports your plants.
  • Compost (or soil conditioner), on the other hand, is organic matter that enriches your soil.

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