Soil is a structure problem before it is a nutrition problem
Indoor plants rarely starve. They suffocate. Roots need air as much as water, and a dense, peat-heavy bag mix compacts into a solid block that holds moisture for a fortnight and leaves nothing for the roots to breathe. Understanding four or five ingredients is enough to build a mix for almost any houseplant you will ever own, and to fix the one you bought at the supermarket.
What each ingredient is actually doing
Coco coir and peat are the sponge — they hold water and give the mix body. Perlite is the white volcanic popcorn that creates air pockets and stops compaction; it does nothing nutritionally and that is fine. Orchid bark adds large, slow-decaying chunks that keep structure open for years, which is why chunky aroids love it. Worm castings supply gentle, slow nutrition and beneficial microbes. Horticultural charcoal absorbs impurities and keeps closed mixes sweet. Coarse sand or pumice adds weight and drainage for top-heavy cacti. Vermiculite holds water and nutrients and belongs in seed-starting, not in an already-wet aroid mix.
Three blends that cover most collections
For general tropicals — pothos, philodendron, peace lily, ficus — use two parts quality potting mix, one part perlite, and a handful of worm castings per pot. For chunky aroids like monstera and anthurium, go three parts orchid bark, two parts potting mix, two parts perlite, one part charcoal; it should look almost too coarse to be soil. For cacti and succulents, invert the ratio entirely: one part potting mix to two parts pumice or coarse grit, so the whole thing dries within days. Phalaenopsis orchids get no soil at all — medium bark chips alone, because their roots are adapted to open air on tree trunks.
Drainage layers are a myth worth abandoning
A layer of gravel at the bottom of a pot does not improve drainage. Water does not cross from fine material into coarse material until the fine layer is saturated, so a gravel base actually raises the waterlogged zone closer to the roots. What genuinely helps is a drainage hole, a mix with enough coarse material throughout, and never letting the pot stand in its own runoff. If you love a cachepot without a hole, keep the plant in a plastic nursery pot inside it and lift it out to water.
Feeding: little, often, and only in growth
Fresh mix carries a few weeks of nutrition and then it is on you. A balanced liquid plant food at half the label strength every second or third watering through spring and summer suits most foliage plants far better than full-strength monthly doses, which spike salts. Fertilizer spikes are convenient but concentrate nutrients in one spot; if you use them, water thoroughly and rotate their position. Stop or halve feeding from late autumn until light returns. Flush pots with plain water every couple of months to wash out accumulated salts — that white crust on the rim is your reminder.
Refresh the mix before the plant demands it
Even a good blend breaks down. Bark decomposes, coir compacts, and after two years the airy mix you made has become dense and water-repellent. Most houseplants want fresh medium every eighteen months to two years, whether or not they need a bigger pot. Tease away the old material from the outer roots, trim anything brown and soft, and repot into the same size container with new mix. Plants often respond to that alone with a flush of growth — no larger pot, no new fertilizer regime, just soil that breathes again.