When sourcing natural bonsai, you must prioritize botanical health and aesthetic maturity. Key specifications include the trunk diameter (caliper), which indicates the tree's age and value, and the nebari (root flare), which should be well-developed and visible. Ensure the potting medium is a professional-grade mix like Akadama, pumice, or lava rock to ensure proper drainage during transit. For B2B buyers, it is critical to verify the species-specific hardiness zone to ensure the plants can survive in the destination climate.