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LECA (expanded clay pebbles)

Also known as Lightweight expanded clay aggregate, Clay pebbles, Hydroton, Semi-hydro

Growing mediumDepends
Expanded clay pebbles (LECA) Photo: Lucis · CC BY-SA 3.0

In short

LECA is clay fired in a kiln until it puffs into light, round, porous pebbles. It is an inert, reusable medium for hydroponics and the semi-hydro method, and is also mixed into potting mixes for aeration.

How it looks

Round, reddish-brown pebbles, typically between a few millimetres and a couple of centimetres across, with a hard shell and a honeycomb of small air pockets inside. They are made by heating clay to about 1,200 °C in a rotary kiln, and are pH near 7.

Signs

New pebbles release fine clay dust that clouds water. Crusty white deposits on pebbles and pots show mineral or fertiliser salt build-up. Roots sitting permanently below the water line can rot if the reservoir is kept too high.

What favours it

In semi-hydro, a plant potted only in LECA sits in an outer container with a reservoir of dilute nutrient solution; the porous pebbles wick moisture upward to the roots. The round pebbles give very good aeration.

Prevention

  • Rinse new pebbles thoroughly before use to remove clay dust.
  • Wash all soil off the roots when moving a plant from soil to LECA.
  • Keep the reservoir low (one grower suggests about one-third of the pot) so upper roots have air.
  • Feed with a nutrient solution made for soilless growing, because LECA contains no nutrients.

Treatment

Start with the first step and move down only if the problem persists.

  1. Flush pebbles with clean water periodically to remove salts.
  2. To reuse, rinse and clean pebbles before repotting another plant.

Pros and cons

Pros

  • Inert, pH-neutral and reusable for years.
  • Excellent aeration around the roots.
  • No organic matter to rot or compact; growers report fewer fungus gnats.
  • Lets water status be seen through clear containers and allows longer gaps between waterings.

Cons

  • Holds no nutrients; plants depend entirely on fertiliser solution.
  • Plants with fine roots may need smaller pebbles or a gentler transition, such as rooting first in sphagnum and perlite.
  • Salt build-up needs regular flushing.

Look-alikes

Lava rock
Lava rock is irregular and jagged, heavier and does not have a smooth rounded shell.
Akadama
Akadama is softer, crumbly granules of volcanic clay that break down over time.

Typical uses

Aroids and many tropical houseplants in semi-hydro; hydroponic vegetables and herbs; also used as a chunky additive in aroid and orchid mixes.

Sources

  1. Expanded clay aggregate — Wikipedia
  2. Episode 205: LECA — Jane Perrone, On the Ledge

Written in our own words from these sources. Check a product label before using any treatment.