Every specialist mix we sell is built from nine raw components, and each one does a specific job: some create air space, some hold water, some hold nutrients, and some provide structure that lasts for years. This page lists all of them with their particle grading, typical Air-Filled Porosity (AFP) and Water-Holding Capacity (WHC), pH and bag prices, so you can adjust one of our mixes or build your own from scratch.
The numbers given for each component are measured on the component on its own. In a blend, AFP and WHC do not add up exactly: small particles settle into the gaps between large ones, so a mix of bark and coir usually has a little less air than the average of its parts. Use the figures as a guide, and use our repotting calculator in recipe mode to see the estimated AFP of a custom blend. If the science is new to you, our guide to air-filled porosity and peat-free substrates explains the principles.
All components are 100% peat-free, screened and bagged by hand at our Yorkshire nursery, and they are the same grades we use in our own glasshouses.
Blending at home
Think about blending in three fractions: a structural fraction that creates air space and lasts (bark, pumice, perlite, charcoal, LECA), a moisture fraction that holds water (buffered coir, coco husk, vermiculite, sphagnum), and a nutrient fraction (worm castings, zeolite). The proportion of each depends on the type of root you are growing for. As a starting point, by volume:
- Thick epiphytic roots with velamen (velvet Anthurium, Philodendron melanochrysum): around 70% structure, 25% moisture, 5% nutrient. Target AFP 40–45%.
- Climbing aroids (Monstera, climbing Philodendron): around 70% structure, 20% moisture, 10% nutrient. Target AFP 35–40%.
- Fine wiry epiphytes (Hoya, Rhipsalis, Dischidia): around 75% structure, 20% moisture, 5% nutrient, using smaller grades of bark and pumice. Target AFP 40–42%.
- Fine feeder-root mats (Alocasia, Colocasia): around 45% structure, 50% moisture, 5% nutrient, using fine bark. Target AFP 25–28%.
- Fine terrestrial roots (Calathea, Maranta, ferns): around 40% structure, 50% moisture, 10% nutrient, using low-EC buffered coir. Target AFP 20–24%.
- Water-storing desert roots (cacti, succulents, caudiciforms): around 70% mineral structure, 20% moisture, 10% nutrient. Target AFP 38–42%.
Blend in a large tub or on a tarpaulin. Pre-moisten the coir and husk first, then add the dry structural components and turn the whole batch over several times so the fine particles are evenly distributed rather than settling at the bottom. Measure by volume with a jug or scoop, not by weight; pumice and charcoal weigh very different amounts per litre. Then adjust for your home: in a dry, centrally heated room or for a forgetful waterer, shift 5–8% from structure to moisture; for a cool room, a humid cabinet or a heavy-handed waterer, shift 5–8% the other way.
Component notes
Coarse Perlite 3–6mm
Expanded volcanic glass. Holds almost no water inside the particle, so it adds air without adding weight or nutrients. Our 3–6mm grade is dust-screened; wet it before blending to keep any remaining fines down. Very light, so it can float to the surface of heavily watered pots.
Volcanic Pumice 4–8mm
Naturally porous volcanic rock, washed and graded. Holds some water inside its vesicles and moves it through the pot by capillarity, so it gives a more even moisture profile than perlite. Adds weight to stabilise climbing plants on moss poles. The main wicking component in our semi-hydro blend.
Orchiata Pine Bark 6–12mm or 12–18mm
Graded, steam-treated New Zealand Pinus radiata bark, aged so it does not lock up nitrogen as it settles. High lignin content means it decomposes over two or more years in a pot. Choose 12–18mm for Anthurium and large aroids, and 6–12mm for Hoya and smaller pots. Soak before use, as dry bark is slow to rewet.
Buffered Coco Coir <3mm screened
Coconut husk fibre and pith, calcium-buffered and rinsed to a starting EC below 0.5 mS/cm so it does not strip calcium and magnesium from your feed. Unlike peat, it rewets readily after drying out. On its own it compacts over time, so always blend with a structural component.
Coco Husk Chips 6–15mm
Chopped and buffered coconut husk. Each chip acts like a small sponge, holding water internally while the gaps between chips stay full of air. A sustainable, peat-free replacement for tree fern fibre in epiphyte and terrarium mixes. Breaks down more slowly than coir but faster than pine bark.
Horticultural Charcoal 5–10mm
Hardwood charcoal, screened to remove dust. Its porous structure provides surface area for beneficial microbes and adsorbs some of the compounds released as organic components decompose. Slightly alkaline, so keep it at 5–10% of a blend. Essential in closed terrariums and long-term mixes.
Organic Worm Castings <2mm
Screened vermicompost from worms fed on plant material. Releases nitrogen and other nutrients slowly and introduces a diverse microbial population. Fine-textured and dense, so it reduces air space if overused; we use 5–10% in our blends. Store loosely closed in a cool place to keep it active.
Zeolite 2–5mm
Natural clinoptilolite, a porous aluminosilicate mineral. Holds positively charged nutrients on its surfaces and releases them gradually, buffering mineral and semi-hydro mixes against swings in feed strength. Also adds weight and permanent structure. Use 5–20% in mineral blends and around 5% in organic ones.
Vermiculite 2–4mm
Heat-expanded mica mineral that holds water and nutrients between its thin layers. Raises moisture retention without the compaction of fine organic material, ideal for Alocasia, Calathea and fern mixes and for seed sowing. Becomes compressed if handled roughly when wet, so blend gently.