A technician kneels beside a two-metre ficus in a bank lobby, working out why the bottom third of the pot has stayed sodden for weeks. The plant is fine. The soil is not — after two years it has slumped, packed down and stopped letting air through.
That is why mineral substrates exist. Soil eventually stops behaving like soil, a whole floor at a time.
A disclosure before we go further: Casa Verde Distribution, which distributes LECHUZA planters and PON substrate in Canada, is our sister company. Here is what the product actually is, and what it isn't.
What is PON, exactly?
PON is a mineral substrate — small stones instead of soil. LECHUZA's product declaration lists pumice, lava and zeolite, in grains of 2–5 mm.
Each mineral does a job. Pumice gives drainage and air-filled pore space (University of Arkansas). Lava gives structure. Zeolite holds nutrients and hands them back, with a very high cation exchange capacity of 100–200 cmol/kg (University of Arizona Extension).
No peat, bark or compost — so it doesn't decompose or shrink the way peat does (USDA-ARS and Oregon State, in HortTechnology).
How heavy is PON compared with soil?
LECHUZA publishes no weight or bulk density for PON anywhere, and sells the weight as a feature: "LECHUZA-PON has an adjusted bulk weight. Your plant is supported firmly in the planter, which is important for bigger plants."
LECHUZA's own online shops list the 12-litre bag at about 10.8 kg — several times heavier per litre than a peat-based mix.
For lobby planters, or bags carried around a building, floor loading is a real question on a large program — ask the building first.
How do you transition plants to PON?
Every LECA guide tells you to rinse the roots bare. In a jar with no drainage, fair enough — soil in standing water stays sodden. A LECHUZA planter is not a jar: the reservoir sits below a separator, and LECHUZA has you top-water for the first twelve weeks with it nearly empty, so that soggy root ball never forms. Hence its own instruction: "the soil does not need to be removed from the roots." Shake off what falls, loosen the root ball, plant.
Rinse when:
- The old soil has fungus gnats. LECHUZA's German FAQ says take it all off — the one thing both camps agree on.
- The PON is not in a LECHUZA planter. Fine in a nursery pot with drainage; a cachepot with none puts you back in LECA conditions.
LECHUZA's own UK sales director recommends a full rinse into 100% PON. Neither side has a study behind it; let the planter decide.
Does PON need fertilizer after six months?
Yes. PON arrives pre-fertilized, and LECHUZA describes the charge as lasting about six months — "after about half a year, the fertilizer's effect in the substrate begins to wear off." Elsewhere the same company says six to eight months.
The declaration lists a solid inorganic multinutrient fertilizer, NPK 15-11-14+2+ME, in encapsulated pellets, pH 8.2 in water, EC 5 mS/m. LECHUZA also says the substrate keeps a stable pH and releases nutrients as needed, which makes feeding a calendar item rather than a guess.
Can you use PON without a reservoir?
Yes. LECHUZA says all PON substrates "can be used in both planters with an irrigation system and in conventional flowerpots or window boxes."
In a reservoir planter, PON's structure keeps the root zone from turning to mud — our companion piece on what self-watering planters fix and what they don't is worth reading first. In a plain pot it behaves like a coarse, free-draining mix: the top dries quickly and you water more often, not less.
A reservoir still holds a permanently saturated zone at the bottom; no substrate makes overwatering impossible.
Where does PON fit in an office plant program?
It suits the plants hardest to reach by hand: large floor specimens, lobby planters, anything in a locked boardroom or on a high shelf. A mineral substrate for office plants is a maintenance decision more than a horticultural one.
Two limits. Media with less organic matter are less attractive to fungus gnats than peat-heavy mixes (University of Wisconsin Extension) — less attractive, not gnat-proof. And it won't stop surface algae or mould; airborne spores settle on any damp surface.
Sourcing LECHUZA PON in Canada is straightforward; deciding which plants belong in it is the harder part. That's what our office plant maintenance service is for.