Direct answer

The three core components are compost (nutrients), sand (drainage) and clay (water retention). Plants need different balances, which is why one mix never fits all.

ComponentAddsRemoves / tradesSource
CompostNutrients, NPK availabilityβ€”Biomass / materials / shops
SandDrainageWater retentionMaterials / shops
ClayWater retentionDrainageMaterials / shops

Where components come from

Components are acquired through materials, biomass and club shops. See the materials hub for acquisition, and the biomass page for the main generator material.

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Evidence note

Component roles are official and observed. Per-plant ratios remain pending the Plant Info sweep.

OFFICIAL

Official game description names compost, sand and clay as soil components.

Steam store
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Component data is a shared record used by soil-mix, NPK and plant pages.