Houseplant guide

Houseplants live in small containers where every choice is concentrated. There is no deep soil to absorb mistakes and no rainstorm to flush the evidence.

At repotting

Blend castings into a complete potting mix at about 10–15% by volume. Keep the remainder appropriate to the plant: bark and coarse mineral particles for epiphytes, a standard airy mix for tropical foliage, or an especially fast-draining blend for succulents.

Do not pot a plant in pure castings. They are an amendment, not a structural medium. Roots need air spaces, and “but it looked rich” is not a drainage plan.

Top-dressing an established pot

1. Check that the pot drains freely.
2. Gently loosen the top surface without tearing major roots.
3. Spread roughly ¼ inch of castings, leaving a gap around the stem.
4. Water slowly until excess drains.
5. Empty the saucer; do not let the pot stand in runoff.

Small-pot amounts

For a 4-inch pot, a tablespoon or two may be plenty. For larger pots, use the ¼-inch layer as the guide rather than guessing by handful. The calculator can estimate a round pot from its diameter.

When to apply

Use castings during active growth, often in spring through early fall for many indoor plants. Reduce amendments when a plant is dormant, stressed, newly moved, or sitting in low winter light.

Diagnose yellow leaves first

Yellowing can come from wet roots, low light, pests, old leaves, temperature stress, pH, or nutrition. Check moisture below the surface, inspect roots and leaves, and review light exposure before feeding.

Salt and water considerations

Minerals from fertilizer and hard water can accumulate in indoor pots. Periodically water thoroughly enough for drainage when the plant and medium allow. Never use castings to mask a crusted, compacted, or sour-smelling mix; repot and correct the root environment.

For houseplants, restraint wins. Add a little castings, preserve pore space, and remember that the most common nutrient in an overwatered pot is regret.