Clay pebbles to increase moisture around indoor plants

Air moisture is important for almost every houseplant, and clay pebbles can increase it for a very affordable price.

Key facts for clay balls & moisture

Time to set up – 5 minutes
Water fill-up – once/twice daily
Cost – a few cents
Effectiveness – high

A layer of expanded clay balls kept moist under your plant will work wonders. It will keep plants from getting brown tips on leaves!

Clay pebbles to raise moisture around houseplants

How to prepare the set-up

Expanded clay layered in a saucer an inch thickThe idea is to set a tray filled with wet clay balls near or under your plant pots.

  • The structure makes clay pebbles an ideal air moisturizer. Evaporation is easy, and these pebbles absorb a lot of water when drenched.
  • Layer the clay balls an inch or an inch and a half thick (2 ½ to 4 cm).
  • Wet the tray in the morning and in the evening.
  • Drain excess water out: clay will only release moisture if directly in contact with air.
  • Keeping water in the tray filled to the brim with water and clay balls drowned inside won’t work very well.

You can rest all your pots atop such a tray. In no time, your plants will turn more lush and lively!

Use rainwater for houseplants. If you haven’t collected rainwater yet, use demineralized water like the one used for ironing clothes.

  • Indeed, if you use normal tap water, minerals build up and block the clay’s pores. This would reduce the amount of water clay balls can absorb and release.

Why clay pebbles?

Expanded clay or leca balls on a glass surfaceClay balls also go by other names: leca (an acronym), hydroton, expanded clay, aggregates or clay pellets and beads, just to cite a few. They’re produced by heating clay up to 2000°F (1200°C), making the gases inside expand to look like a sponge or honeycomb.

  • This happens naturally in volcanoes when erupting. It explains why pumice and, to a point, pozzolan, is so light!

The bubbles in the pebbles are perfect to absorb water and air. The thin clay walls are porous and let water seep in and out. The consequence? Expanded clay pellets make ideal air moisturizers thanks to their structure and materials.

Water will evaporate from the surface of the clay balls and enter the air around it. Thanks to capillarity, water deeper inside the clay ball will seep to the surface for evaporation to continue.

Clay pellets are always available in garden stores. They’re often used as a cool mineral mulch and as an additive to soil mix since they increase water retention and drainage.

Replenishing water in the clay pebbles

How often to add water

After a few hours, most of the water will have evaporated already. At the end of the day, the clay pebbles will usually be totally dry.

For maximum air humidifier effect, replenish water on your clay pellets twice a day, morning and evening.

On hot days, a third top-up might be necessary in the afternoon.

If you notice pebbles are drying up very fast, you can also add a bit more water than necessary to let the pebbles wallow in a little water. For example, a quarter-inch or 5mm water level at the bottom will serve as a “water reserve”. The pebbles will draw moisture up from it during the day.

Best way to top-up water

  • Remove the potted plant and set it aside, on a plate or dish to protect your furniture.
  • Near a sink, fill the tray and pebbles with water and let it sit for twenty or thirty seconds.
  • This gives each pebble time to absorb water deep inside.
  • Hold the pebbles in place with a cutting board or a “splatter screen” (used to keep oil in the pan when frying or sautée-ing vegetables).
  • Dump excess water with a funnel back in its container (no point in wasting rainwater, if only to spare effort collecting it).

Another option is to find a glass or bottle that contains just enough volume to douse the pebbles well.

  • That way, simply fill the glass to the brim, lift the pot up, and pour on the pebbles as evenly as you can.
  • Air moisture will increase as the expanded clay releases water vapor.

Remember to use distilled water or rainwater for this as much as you can. In fact, whatever technique you use to raise air humidity around plants, it’s best to avoid tap water if you can.

Cleaning and rinsing the pebbles

Every now and then, like once a month, it helps to replace and clean the pebbles to keep pests and insects out. It also makes sure algae doesn’t develop.

It’s also possible to just rub the pebbles around for a few minutes in a basin of water. Spraying them with a nozzle hose in a barrel with holes at the bottom also works great.

If they’re very dirty:

  • pour the expanded clay balls or pebbles in an old sock (or several) and tie it shut.
  • It’s also possible to use a mesh pouch, as long as it closes tight.
  • Use a powerwasher to blast through the socks.
  • This will dislodge the algae and dust, which will filter out of the cloth.

Once they’re clean, sterilize them in the following manner:

  • Boil the clay pebbles in a large cauldron or kettle for 8 to 12 minutes, in normal water.
  • No need to add anything to the water (bleach, hydrogen peroxide, etc). The heat is enough to kill any bugs, algae and fungus off.

Which plants to use moisturizing clay pebbles for

Plants that benefit most from this technique are those that tend to release lots of water to the air.

Problems that might arise

Mineral deposits due to using tap water

On one hand, only using tap water will slowly clog the pores of the clay balls. This means they won’t absorb water any more. In the end, they won’t be as effective. They’ll still do the job, but no better than if you’d used regular gravel picked up from the ground or driveway.

Insects and pests

If you don’t clean the pebbles from time to time, the clay pebbles will attract pests. These can include red spider mite, thrips, scale insects and others.

  • This won’t be a problem if you replace or sterilize the pebbles monthly.

Smart tip about using clay pebbles for extra moisture

Resting your pots atop these clay balls are an excellent way to prevent root rot. The bottom of the pot is never in contact with wallowing water, protecting the roots inside.

Wet clay pebbles are excellent moisturizers.


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Clay balls in water reserve by Rosalyn & Gaspard Lorthiois, own work
Pouring leca balls by Rosalyn & Gaspard Lorthiois, own work
Clay balls up close by Rosalyn & Gaspard Lorthiois, own work
Wet clay balls by Rosalyn & Gaspard Lorthiois, own work