LECA and Pon in Self-Watering Pots

Why this is the right pot for it

Peat-based mixes have one failure mode in a reservoir planter, and it is structural rather than biological. Organic components decompose. As they do, the mix loses pore space and compacts, and a compacted column in a permanently moist pot holds more water and less air than the plant wants. That is the slow version of the problem our root-rot page describes.

Mineral grains do not do that. Fired clay, pumice, zeolite and lava do not decompose and do not collapse, so the air-to-water ratio you plant into is roughly the ratio you still have in three years. In a pot you are not going to repot often, that stability is worth something real.

NC State Extension makes the general point about containers: the potting soil used to grow container plants is really not soil at all, and field soils are not used because they retain too much water and have too little pore space. A mineral substrate is that logic followed to its end.

The trade, stated plainly

This site exists for people who kill plants by forgetting them. So here is the honest version of what a soil-free reservoir pot asks of you.

What you gain. No decomposition, no compaction, a visible water level if the inner pot is clear, roots that are easy to inspect, and a substrate you can rinse and reuse rather than replace. Materially less risk of the soggy-column rot that kills plants in reservoir pots.

What you give up. Expanded clay is inert. It contains no nutrients and holds very few by itself, which means every nutrient the plant receives comes from your fertilizer, every time. Miss a few feeds in a peat mix and the mix carries the plant for a while. Miss a few feeds in plain LECA and there is nothing to fall back on.

How we judged these

Is it designed for sub-irrigation? A bag of hydroponics pebbles and a substrate engineered for reservoir planters are not the same product even when the mineral is similar. Grain size and the proportion of fine material decide how high water wicks, which in a reservoir pot is the whole mechanism.

Does it carry nutrition, and do you want it to? This cuts both ways and is not a simple ranking. Pre-fertilized means a soil-free pot is not instantly a feeding problem. Fertilizer-free means you control the dose, which matters in a container you cannot flush on demand.

What is actually published? The usual test on this site. Volume in liters beats weight in pounds, because you are filling a pot rather than lifting one. A published composition beats “premium grow media”.

Cost per liter. Filling a floor planter takes more substrate than people expect, and this category has a wide spread.

LECA and Pon are not the same thing

They get used interchangeably and they behave differently, which matters because the choice changes how you water and feed.

LECA is lightweight expanded clay aggregate: clay fired until it puffs into porous pebbles, typically 4 to 16 mm. The pebbles are large, so the gaps between them are large, so a LECA column holds a lot of air and wicks water a relatively short distance up. It is inert and chemically does nothing.

Pon-type substrates are blends of smaller mineral grains - zeolite, pumice and lava in LECHUZA’s case. The smaller, more varied grain size means finer pore spaces, which wick water higher than coarse LECA will. Zeolite also has genuine cation-exchange capacity, meaning it holds nutrient ions rather than letting them wash straight past, which is the one chemical difference that matters.

For a reservoir planter that distinction favours a Pon-type blend: better capillary rise from the water level up into the root zone, and some nutrient-holding capacity. For a drainage layer at the bottom of a big planter, or for a plant you want maximum air around, coarse LECA is the better material.

The figure LECHUZA does not publish

PON ships with a coated fertilizer in it, which is the main reason to choose it over plain clay. How long that fertilizer lasts is published as six months on some retail listings and twelve months on others, and we could not reach a LECHUZA product page to settle it - the manufacturer’s own URLs returned errors when we checked.

So we are not going to tell you which it is. What we will say is how to act without the number: treat the included fertilizer as a head start rather than a schedule, and begin feeding a diluted complete liquid a few months in, watching the plant rather than the calendar. New growth that comes in paler or smaller than the leaf below it is the signal.

This is the same honesty problem that runs through the whole category. The ceramic self-watering pots mostly publish no reservoir capacity. Most olla makers publish no capacity either. A fertilizer duration published as both 6 and 12 months is the substrate version of the same gap.

Feeding a soil-free reservoir pot

This is the part people underestimate, so it gets its own section.

In plain LECA, the substrate contributes nothing. Your fertilizer is the entire nutrient supply, which means it needs to be a complete one - not just nitrogen, phosphorus and potassium, but calcium, magnesium and the micronutrients too. A basic NPK feed in an inert substrate produces deficiencies that look like disease.

That is the argument for a feed that publishes its full analysis, and it is the same argument that our fertilizer page makes for reservoir pots generally - except that in an inert substrate it stops being a refinement and becomes the requirement.

The other half is salt. Fertilizer is salt, and a reservoir pot does not flush itself. UMD Extension’s leaching instruction - at least twice the volume of the pot, every four to six months - applies at least as much to a mineral substrate as to a peat one. The good news is that rinsing LECA is easy and it comes out clean, which is more than you can say for flushing a compacted peat column.

Moving a plant from soil into LECA

Worth knowing what you are committing to, because this is not a potting-on.

Every trace of old mix has to come off the roots, which means rinsing them clean. Roots grown in soil are structurally different from roots grown in water-and-air, so the plant typically sheds some of them and grows replacements, and it will look unhappy for weeks while it does. Plants with fine, dense root systems take this worse than plants with thick roots.

A healthy plant in a mix it is doing fine in is not a candidate. The good candidates are a plant you are repotting anyway, a cutting you are rooting from the start, or a plant you have just rescued from an overwatered pot and already have bare-rooted in your hands. That last case is the genuinely strong one: if rot took the plant once, an inert substrate removes the decomposing organic matter that made the pot hospitable to it.

Rinsing and reusing it

Two practical points the cheap bags tend not to mention.

Rinse before first use, every time. Expanded clay arrives with fired clay dust in the bag, and that dust is fine enough to migrate down and settle into the bottom of a planter where it defeats the drainage you bought the pebbles for. Rinse until the water runs clear. Soaking first also matters: dry pebbles will pull water out of the reservoir to saturate themselves before any of it reaches a root.

Then keep it. This is the one genuine economic argument for the expensive bags. A peat mix is spent after a couple of years - it has decomposed, which is the whole problem. Fired clay and mineral grains come out of a repotting exactly as serviceable as they went in. Rinse, and they are ready for the next plant.

Over three or four repottings that closes most of the price gap against bagged mix. It is also why the published volume matters more than the published weight: you are buying a durable asset by the liter, not a consumable by the pound.

Which plants suit it

Aroids take to a mineral substrate best - monstera, philodendron, pothos, anthurium and most thick-rooted tropicals. Their roots want air and they tolerate a visible water table.

Plants that do not suit it are the ones that do not suit reservoir pots generally. Succulents and cacti want a drying cycle that a standing water level does not provide, which is the argument our succulent pot page makes at length. Orchids are a special case: a bark mix is the conventional default and the orchid page explains why, though inert media are genuinely used for them by growers who feed precisely.

Fine-rooted plants like calathea and maidenhair fern are the ones to be most cautious with, both because the transition is hardest on them and because they are least forgiving of a feeding gap.

What we would buy

A Lechuza-style reservoir planter you want to go soil-free in: PON. It is made for the pot, it wicks properly, and the included feed covers the first stretch even if nobody will tell you how long that is.

You already have a complete liquid feed and a routine: BASICPON, or Hydroton if you want coarse clay. Controlling the dose yourself is worth more than a head start you cannot date.

Filling something large: the PGN pebbles. Cheapest per liter, and the published volume-and-weight pairing is the only one here you can price-check honestly.

You just want the plant to live and you are not a hobbyist: none of these. Buy a reservoir planter that publishes its capacity and fill it with a mix suited to it. That is the lower-effort path and we would rather say so than sell you a bag.