From our perspective, the single most critical factor in your soil mix is its ability to let water pass through quickly. Our roots are highly susceptible to rot if left sitting in saturated, oxygen-deprived soil. A dense, water-retentive mix is a death sentence. We require a growing medium that provides a perfect balance: it must hold enough moisture to hydrate our roots but must also allow excess water to drain away almost immediately. This ensures our root zone has access to the vital oxygen we need for respiration and nutrient uptake. Think of it as needing a well-aerated, fluffy bed, not a wet, compacted one.
The perfect soil mix for us mimics the well-draining, slightly gritty conditions we evolved in. A high-quality, sterile potting mix should form the base (roughly 60-70%). However, this base must be heavily amended to achieve the drainage we demand. You must incorporate coarse materials like perlite or pumice (20-30%), which create essential air pockets and prevent compaction. Adding a smaller portion of coarse sand or fine gravel (around 10%) further improves drainage and adds weight to the pot, preventing it from tipping over as we grow. A handful of organic matter, such as well-rotted compost or worm castings, is beneficial for providing a slow release of nutrients and improving microbial life, but it should not dominate the mix.
We absorb nutrients most efficiently when the soil pH is in the slightly acidic to neutral range, ideally between 5.5 and 6.5. While we are somewhat adaptable, a pH within this range ensures that essential micronutrients, particularly iron, remain soluble and available for our roots to absorb. An incorrect pH can lead to nutrient deficiencies, evident in yellowing leaves (chlorosis) despite proper feeding. Using a potting mix that is not pre-amended with lime is a good start. You can help maintain this pH by occasionally watering with a slightly acidic fertilizer or, if necessary, amending the soil with sulfur based on a soil test.
Contrary to popular belief, we are not heavy feeders in terms of soil richness. We actually thrive in soil that is moderately fertile. An overly rich, nitrogen-heavy mix will encourage an explosion of weak, leafy green growth at the expense of our magnificent floral displays (which are actually colored bracts). The nutrients we need are best provided through a consistent feeding schedule with a fertilizer high in phosphorus and potassium rather than being baked into the soil mix itself. The organic compost or worm castings in the mix provide a gentle baseline of fertility, but the primary nutritional support should come from your fertilization routine during our active growing season.
