How to Use Clay Pebbles in Hydroponics: Rinsing, Soaking and Reusing
Clay pebbles are one of the most popular growing media in hydroponics. They are clean, reusable and give roots plenty of air. But many growers skip the preparation, or throw them away after a single crop, which wastes money and can cause problems in your system. Here is how to get the best from them.
What are clay pebbles?
Clay pebbles are small balls of clay that have been fired in a kiln until they expand and fill with tiny air pockets. You will also see them called expanded clay, LECA (lightweight expanded clay aggregate) or hydroton. They are inert, so they don't add nutrients or break down over time. Good quality pebbles such as CANNA Aqua Clay Pebbles are made from clay with a low soluble salt content, which makes them well suited to recirculating hydroponic systems.
Pros and cons of clay pebbles
| Pros | Cons |
|---|---|
| Excellent drainage and plenty of air around the roots | Hold less water than coco or rockwool, so they dry out faster |
| Reusable for many crops if cleaned properly | Need rinsing and soaking before first use |
| pH neutral and don't break down | Heavier than perlite and bulky to store |
| Clean and easy to handle | Roots grip them tightly, which makes cleaning slower |
Which systems are clay pebbles good for?
- Flood and drain: the classic use. Pebbles drain quickly between floods, so roots get plenty of air. See our guide to how flood and drain works and our flood and drain systems.
- Drip systems: a common choice in dripper pots, as long as you feed often enough. See dripper systems and accessories.
- Deep water culture and net pots: pebbles hold the plant upright in the net pot while its roots grow down into the solution.
- Mixed into coco or soil: mixing clay pebbles or perlite through coco or soil adds air and drainage. Mix them through the medium rather than putting a layer at the bottom of the pot: a drainage layer doesn't actually help water drain and can leave the medium above it wetter.
- Top dressing: a thin layer on top of coco or soil keeps the surface dry, which helps discourage algae and fungus gnats.
How to prepare new clay pebbles
- Rinse off the dust. New pebbles are dusty. Put them in a bucket with holes in the bottom, a colander or a mesh bag, and rinse until the water runs clear. Do this outside rather than in a sink, as clay dust can settle in drains. Dust left on the pebbles can cloud your nutrient solution and clog pumps, drippers and air stones.
- Soak them. Soak the rinsed pebbles in clean water for at least 6 hours, ideally overnight. Dry pebbles float and soak up some of your nutrient solution when they first get wet. Pre-soaking fills the air pockets with water so they settle properly.
- Adjust the pH of the soak water. Set the soak water to the pH you will run in your system, usually between 5.5 and 6.5 for hydroponics. Check the pH again after soaking. If it has moved a lot, give the pebbles another soak before using them. Our guide to pH explains why it matters.
- Fill your pots. Fill your pots or net pots and settle the pebbles by gently tapping the side of the pot.
How to plant into clay pebbles
Seeds are too small to start directly in pebbles, as they fall through the gaps. Start seeds or cuttings in a propagation cube such as rockwool or Root Riot, then set the cube into the pebbles once roots appear from the bottom. Browse our cutting and seedling media and propagation range.
Because pebbles drain so quickly, young plants need watering more often until their roots reach the solution or the flood zone. Hand water the cube for the first few days if needed.
How many clay pebbles do you need?
As a rough guide, you need about the same volume of pebbles as the pots you are filling, plus a little extra to allow for settling. A 45 litre bag fills roughly four 10 litre pots, while a 20 litre bag suits smaller systems and net pots.
How to clean and reuse clay pebbles
One of the big advantages of clay pebbles is that you can reuse them crop after crop. Clean them properly so you don't carry salts, old roots or pathogens into your next grow:
- Remove the root mass. Lift out the plant and break up the root ball. Shake and pick out as much root as you can. Roots crumble away more easily once they have dried.
- Soak with an enzyme product. Soaking the pebbles in water with an enzyme product such as Bio Nova BN-Zym helps break down the fine roots left on and in the pebbles.
- Rinse well. Rinse and agitate the pebbles to wash out loose root material and debris.
- Sterilise. Soak them in a horticultural sterilising solution, such as Silver Bullet Roots at its between-crops dose, to kill any pathogens. Rinse thoroughly afterwards.
- Flush out salts. A final soak in clean, pH-adjusted water helps remove leftover nutrient salts. If you can see a white crust on the pebbles, give them a longer soak.
- Dry and store. Spread them out to dry completely before storing them in a sealed bag or tub, so nothing grows on them between crops.
Throw away any pebbles that are cracked or crumbling, as broken pieces can block pumps and drippers.
Clay pebbles vs other growing media
| Medium | Holds water | Air for roots | Reusable | Best for |
|---|---|---|---|---|
| Clay pebbles | Low | Very high | Yes | Flood and drain, drip, net pots |
| Perlite | Low | High | Rarely | Mixing into coco or soil |
| Coco coir | High | Good | Sometimes | Hand feeding and drip systems |
| Rockwool | High | Good | No | Propagation and slab systems |
Browse clay pebbles and perlite, coco coir, rockwool or our full range of growing media. If you are weighing up coco, our coco vs soil guide is a good place to start.
Clay pebble FAQs
Do you need to rinse clay pebbles?
Yes. New pebbles carry clay dust that can cloud your solution and block pumps, drippers and air stones. Rinse them until the water runs clear.
Do you need to soak clay pebbles before use?
It is strongly recommended. Soaking for at least 6 hours, ideally overnight, in pH-adjusted water stops them floating and soaking up your nutrient solution, and lets you check the pH before planting.
Can you reuse clay pebbles?
Yes. Remove the roots, soak, sterilise, rinse and dry them, and they can be reused for many crops.
Are clay pebbles the same as LECA and hydroton?
Yes. LECA is the general name for lightweight expanded clay aggregate, and hydroton is a brand name that many growers use for any expanded clay pebbles.
Can you grow in clay pebbles alone?
Yes, in hydroponic systems that feed regularly, such as flood and drain or drip. In hand-watered pots they dry out too quickly, so mix them with coco or soil instead.
Pick up clay pebbles in Rainford
We stock CANNA Aqua Clay Pebbles in 20 litre and 45 litre bags. Call 01744 382 066 or visit us at Unit 5A Rainford Industrial Estate, St Helens, WA11 8LS.