From our perspective as Crassula plants, our most critical demand is a potting mix that never leaves our roots waterlogged. Our roots are not adapted to constant moisture; they are designed to absorb water quickly during rare rainfalls and then breathe. A mix that retains too much water suffocates our root system, creating an anaerobic environment that leads to root rot—a death sentence for us. Therefore, the primary goal of any mix you create must be to facilitate the immediate escape of excess water. Every ingredient you choose should serve this purpose of creating air pockets and preventing soil compaction.
We thrive in a gritty, predominantly inorganic environment that mimics our native, rocky habitats. The base of your DIY mix should be coarse, sharp materials that do not break down easily and maintain their structure. Our preferred mineral components include coarse sand (horticultural grade, not fine beach sand), perlite, and pumice. Perlite is excellent for aeration and keeping the mix light, while pumice provides weight to stabilize our top-heavy forms and also absorbs a small amount of moisture without becoming soggy. A ratio where these inorganic materials constitute 50-70% of the total volume is ideal. This ensures our roots have ample space to grow and access oxygen, which is just as vital as water.
While we require excellent drainage, we still need some organic matter to provide anchorage and a slow release of nutrients. However, from our point of view, less is definitively more. A standard potting soil is too dense and moisture-retentive on its own. You must use it sparingly and ensure it is a well-draining cactus or succulent mix. This organic component acts as the "sponge" in the mix, holding onto just enough water and nutrients for our roots to uptake over a few days. It should never be the dominant part of the blend. Peat-based soils are problematic as they become hydrophobic when dry and are difficult to re-wet; we prefer coir-based mixes or those with composted pine bark for better wettability and structure.
Here is a mix recipe that our root systems would find perfectly comfortable: Combine two parts of a mineral grit (e.g., one part perlite and one part coarse sand) with one part of a well-draining cactus & succulent potting soil. This creates a blend that is roughly ⅔ inorganic and ⅓ organic. You can adjust this ratio based on your local climate; in more humid environments, we would appreciate even more perlite or pumice (a 3:1 ratio of inorganic to organic), while in very hot, dry climates, a slightly higher organic content might be acceptable to prevent us from dehydrating too rapidly.
Please understand that certain common gardening practices are harmful to us. We are deeply averse to mixes containing water-retentive crystals, heavy clay soils, or fine, silt-like sand that compacts and chokes our roots. Furthermore, any mix that lacks drainage holes in the pot is a death trap, no matter how perfect the recipe. Finally, regular garden soil is a host to pathogens and insects we are not equipped to handle and it compacts severely in containers, so it must never be used.
