potting soil; planting mix; compost
Refers to soil or growing medium prepared for container gardening, seed starting, or cultivation. Often a blend of materials like peat, perlite, and compost.
I bought some potting soil at the home center.
This planting mix drains well.
堆肥 is compost or manure used as fertilizer, whereas 培養土 is a balanced growing medium for plants.
Compound of 培養 (cultivation) and 土 (soil).