For best drainage in planters from our factory, I recommend a custom blend that prioritizes aeration and water flow while retaining enough moisture for plant roots. The ideal mix is: 50% high-quality potting soil (lightweight and sterilized), 30% perlite or coarse horticultural vermiculite (for pore space and drainage), and 20% well-rotted compost or coconut coir (to hold nutrients and moisture without compaction). Avoid using garden soil or heavy clay-based mixes, as they tend to compact and suffocate roots in enclosed planters. Our factory designs planters with drainage holes, but the soil composition is critical: a layer of gravel or clay pebbles at the bottom is not necessary and can actually create a waterlogged zone; instead, focus on the entire mix being uniformly draining. For succulents and cacti, increase perlite to 50%. For thirstier plants, add more coir. Always test drainage by saturating the pot and ensuring water flows freely from the holes within 10-15 seconds. This professional-grade mix replicates the best nursery conditions and prevents root rot, ensuring your plants thrive.