Semi-Hydro: PON vs LECA

What You’ll Learn in This Article

You’ll discover:

• What semi-hydroponics really is (and what it’s not)
• How LECA, PON, and Ceramsite differ in structure, chemistry, and care
• The truth about Lechuza-PON as a brand, not a generic product
• How to make your own DIY PON-style mix
• The pros, cons, and myths around semi-hydro systems
• How these compare to a traditional indoor soilless mix
• When switching makes sense, and when it doesn’t

By the end, you’ll know exactly what separates PON from LECA and feel confident choosing which, if either,is right for your plants.

TL;DR (Too Long; Didn’t Read)

• PON (as a general term) refers to mineral-based mixes of pumice, lava, and zeolite. Lechuza-PON is a specific branded version with added slow-release fertilizer.
• LECA is expanded clay, it's inert, clean, and reusable, but with no nutrient buffering.
• PON holds more water and nutrients, while LECA offers higher airflow but less forgiveness.
• Neither is “set and forget.” Both require proper fertilizing, flushing, and reservoir management.
• For most indoor growers, a high-quality soilless mix remains more forgiving and biologically active.

The Semi-Hydro Hype — And What’s Real

Scroll through almost every social media influencer's feed and you’ll see them everywhere: clear pots filled with round clay balls, or pristine white mineral chunks, and roots more visible than a streaker heading out the exit at a greenhouse. “No soil! No rot! No pests!” the captions promise.

It’s called semi-hydroponics, or“semi-hydro” for short, also known as Passive Hydroponics and it’s become one of the trendiest ways to grow indoor plants. At the centre of that trend are two primary material choices: LECA (Lightweight Expanded Clay Aggregate) and PON, a mineral-based substrate that’s often confused with a brand name, Lechuza-PON.

Both claim to deliver cleaner roots, fewer pests, and easier care. But do they actually live up to the hype? And which one, if either, is the better choice for your plants and your sanity? For reference, I've been growing vegetables in LECA, and using hydroponic substrates and media in various capacities across my plants and outdoor garden for about 25 years.

Let’s unpack what semi-hydro really means, how LECA and PON differ, and whether either one can truly replace a good old-fashioned soilless mix.

What “Semi-Hydro” Actually Means

Semi-hydroponics is a form of passive hydroponics, you grow plants in an inorganic, inert medium that sits above a reservoir of nutrient solution. The medium wicks water upward, creating a moisture gradient from wet at the bottom to drier at the top.

The idea is simple: water less often, get steady moisture, and keep roots oxygenated.

But here’s the truth that social media often skips, semi-hydro isn’t magic. It’s physics, chemistry, and consistency. You’re trading the self-regulating qualities of organic mixes for full control over nutrients, water, and pH.

Key semi-hydro concepts:

• Wicking: Capillary movement of water upward through the medium.
• Reservoir: The nutrient solution stored at the bottom.
• AF Porosity (Air-Filled Porosity): How much air remains in the pot after watering, crucial for oxygen supply.
• CEC (Cation Exchange Capacity): How well the medium can hold onto nutrients like calcium or potassium.
• EC (Electrical Conductivity): A measure of how concentrated your nutrient solution is.

Understanding these basics is what separates a thriving semi-hydro setup from a swamp of sadness.

Pro Tip: Semi-hydro success depends on oxygen as much as water. Keep the reservoir shallow enough that at least half the root mass lives above the saturated zone.

Meet LECA: The Clay That Started It All

LECA, short for Lightweight Expanded Clay Aggregate, was originally developed as a lightweight construction material in about 1915, but 35+ years later growers discovered its value for use in hydroponic systems. When clay is heated to extreme temperatures around 1,200°C/2,100°F, it expands like popcorn, forming lightweight, porous balls that hold both air and water, making them perfect for supporting plant roots in semi-hydro setups.

Each sphere has a dense outer shell and a honeycombed core. This structure gives LECA its dual personality: it both holds water and leaves space for air.

Click here for an Amazon Link

Benefits of LECA:

When used for indoor plants, those round balls create a clean, airy environment for roots. They’re inert, reusable, and virtually pest-free.

• Highly aerated, reducing the risk of oxygen deprivation.
• Reusable, just wash and sterilize between uses.
• Inert, meaning it won’t alter nutrient chemistry.

Drawbacks:

• No nutrient-holding capacity (very low CEC).
• Must rely entirely on nutrient solution.
• Inconsistent wicking between brands.

Why All LECA Isn’t Created Equal

Different manufacturers produce LECA with varying porosity, density, and shell thickness.

Some brands, like Hydroton (my personal choice), sink immediately and wick evenly. Others float until fully saturated or hold less water because of thicker outer shells. You’ll also find big differences in dust levels and ball size uniformity.

Pro Tip: You don't gain a lot of benefits for rinsing LECA before use, but dust and manufacturing residues can raise EC levels that could potentially harm roots during transition. Personally, I give them a quick rinse, but am not too anal retentive about it.

In essence, LECA is hydroponic scaffolding: it gives roots structure and airflow, but zero food or buffering. It’s up to you, the unlikely gardener, to deliver every nutrient, perfectly balanced, in liquid form for your plants to benefit from.

What Is PON (and Why Everyone Argues About It)

Here’s where things get confusing: PON started as a brand name, not a generic term.

The Origin: Lechuza PON

Lechuza-PON is a proprietary mineral substrate developed by the German company Lechuza, best known for its self-watering planters. According to Lechuza, “PON” stands for Product of Nature, and it’s made from:

• Pumice (lightweight volcanic glass)
• Lava rock (scoria)
• Zeolite
• A coated, slow-release fertilizer

The formula was designed to work perfectly within Lechuza’s self-watering system, wicking moisture while maintaining stable aeration.

It’s a premium, ready-to-use medium that buffers nutrients and stabilizes pH better than LECA because zeolite adds cation exchange capacity (CEC), essentially acting as a nutrient “sponge.”

The Generic Evolution: “PON-Style Mixes”

Over time, plant hobbyists adopted the word “PON” to describe any inorganic mix inspired by Lechuza’s formula, usually made of pumice, lava rock, and zeolite.

You’ll now find endless “DIY PON” recipes, online sellers offering “PON-style substrate,” and even other brands like Natura-PON™ or Bio-PON, all loosely based on the same principle: a balanced, mineral mix for semi-hydroponic growing.

So to be clear:

• Lechuza-PON is a specific branded product.
• PON in general use means any similar mineral blend.

And while Lechuza didn’t invent mineral substrates, they did popularize this particular trio, pumice, lava, and zeolite, in the houseplant community.

Making Your Own DIY PON Mix

If Lechuza-PON is often hard to find or too pricey for a bag of minerals, you can easily build your own version using locally available materials. A simple starting point:

• 4 parts pumice - Amazon Link
• 2 parts lava rock or scoria - Amazon Link
• 1 part zeolite - Amazon Link

I'd suggest looking for a local hydroponics supplier in your area, rather than buying from Amazon since you can avoid shipping costs if you can buy and pick up locally.

Some growers add a small portion of perlite to increase airflow or a coated slow-release fertilizer (like Osmocote) to mimic the built-in feed.

The key is particle diversity: pumice provides structure and moderate moisture; lava rock adds airflow; zeolite adds nutrient retention and buffering. Together, they create a root zone that feels more stable than LECA’s smooth spheres.

Pro Tip: Always rinse pumice and lava rock before use. Volcanic dust can clog wicking and alter pH similar to LECA dust.

Ceramsite and Other Clay Aggregates

“Ceramsite” and “Hydroton” are close relatives of LECA, fired clay pellets that behave similarly but vary in density, shape, and porosity.

Ceramsite is often denser and slightly rougher, making it more stable for tall or top-heavy plants. However, like LECA, it has very low CEC and no nutrients of its own. It also does not wick as well, and is often marketed with a colored coating which I think looks like clown turds, but to each their own.

So while LECA, Ceramsite, and PON all fall under the umbrella of inorganic, mineral-based growing media, their behaviour differs significantly depending on structure and chemistry.

PON vs LECA vs Soilless Mix: A Practical Comparison

When you strip away the hype, all three systems, PON, LECA, and traditional soilless mixes, can grow healthy plants. The key difference lies in how much control you want and how much you trust yourself to manage it.

Myth Check: The “Easier” Myth

Myth 1: “Semi-Hydro Is Easier Than Soil”

Semi-hydro is different, not easier. You swap “remember to water” for “remember to mix nutrients and flush salts.” Plants can still rot, especially if reservoirs stay too deep or stagnant.

Semi-hydro works beautifully for methodical growers who like consistency—but it punishes neglect just as easily as overwatering does in soil.

Myth 2: “LECA Prevents Root Rot”

LECA helps reduce oxygen deprivation, but rot is still possible if water levels stay too high. It’s not the balls that prevent rot, it’s the air gaps.

Pro Tip: Keep 2/3 of your pot height as air space above the water line. Roots need access to both oxygen and moisture. See Leca Column Above

Myth 3: “No Pests in PON or LECA”

True (mostly), you’ll see a lot less fungus gnats since there’s less decomposing organic matter, but you can still occasionally get them from algae build up. You also don't eliminate spider mites, thrips, and/or mealybugs, and algae and biofilm can invite a different kind of mess if you never rinse or sterilize.

The Science of Why They Feel Different

LECA acts like a reservoir wall: it holds some water inside but can dry fairly quickly between spheres. Nutrients aren't stored in it, so your plants live or die by your solution mix and the wicking of the nutrient solution.

PON, with zeolite and pumice, actually stores and releases nutrients slowly, creating a more buffered environment (time limited as it degrades). That’s why some people find it “safer” as it forgives minor feeding errors and can help to stabilise pH.

And our more traditional soilless mixes? They’re the middle ground. They manage oxygen, moisture, and nutrient retention naturally, without you needing to check EC or pH every week.

Choosing What’s Right for You

Every unlikely gardener has a comfort zone. The trick is finding the medium that matches your habits and interestes, not forcing your habits to match the medium.

If you’re drawn to LECA, you probably value simplicity and control. LECA is clean, reusable, and nearly indestructible. It’s ideal if you want to see your root system, control exactly what goes in, and avoid the mess of a more organic type of media. It suits growers who:

• Like a minimalist setup that’s easy to sterilize
• Enjoy mixing nutrient solutions and tracking EC or pH
• Don’t mind a bit of maintenance, like rinsing and flushing
• Grow compact plants or species that prefer higher airflow at the roots

LECA gives you precision and transparency, but very little buffering. If you miss feedings or overcompensate, the plant feels it fast.

If you lean toward PON (or a PON-style mix), you’re probably looking for a little more cushion. The zeolite and pumice act like built-in safety nets, holding water and nutrients longer while moderating pH. PON suits growers who:

• Want semi-hydro control without constant tweaking
• Prefer a bit more moisture retention and nutrient stability
• Like growing thirstier plants or larger specimens
• Don’t want to commit to mixing fertilizer every watering

PON is essentially semi-hydro with training wheels, it forgives the small mistakes LECA exposes.

And if you prefer to set it and forget it, or if your environment swings in humidity and temperature, a soilless mix remains the easiest to manage. It’s less sterile, more structurally and biologically complex, and doesn’t punish inconsistency.

In short:

Soilless mix = porosity balance, least control, most forgiving.

LECA = sterile precision, maximum control, minimal forgiveness.

PON = balanced buffer, moderate control, more forgiving.

Pro Tip: Test semi-hydro on one or two healthy plants first. Compare growth and management with the same species in your usual grow mix. The real teacher is the difference you see.

Wrapping It Up

So which is better, PON or LECA?

Like most things in an unlikely gardener's world, that depends on what you want from your growing experience.

• LECA is clean, simple, and minimalistic, but entirely dependent on you for nutrients.
• PON (especially PON-style DIY blends) adds buffering and structure, giving a bit of safety net for your mistakes.
• Soilless mixes remain the most natural, forgiving choice for most indoor environments.

Semi-hydro isn’t really easier, or the “future of plant care.” It’s just another way to understand water, oxygen, and nutrient balance, and for the right grower, it’s a deeply rewarding one.

FAQ

Q: Can I move plants from soil to PON or LECA directly?

Yes. Rinse roots well and remove all loose organic debris. Transition during active growth if possible, and expect an adjustment period while the old soil roots rot away, and new water roots grow. Swapping any media is a risk, and it's not uncommon for a plant to take a pretty big hit to its health when moving over to semi-hydro. Like any sort of gambling, only risk what you are prepared to potentially lose.

Q: Can I move plants back to soil after trying semi-hydro?

Semi-Hydro remorse is a real thing, and yes, you can always swap back. I'd suggest waiting 6 months to a year, so your plant fully recovers from the initial transplant shock. Follow the same rules as moving from soilless to hydro, but in reverse. You will again have a transition period while water roots rot to be replaced with soil roots.

Q: How often should I change the nutrient solution?

It's best to completely swap out your nutrient solution every 2–3 weeks, or when EC rises above target range. Always rinse and flush with plain water first.

Q: Do I need special fertilizer for semi-hydro?

Use a complete hydroponic nutrient formulated for inert media, one that includes micronutrients and calcium/magnesium. If you've followed me for any length of time then you know my go-to is Foliage Pro from SuperThrive.