Clay Pebbles




  • Ideal substrate for flood and drain
  • Increases aeration when added to another media
  • Improves drainage when added to another media
  • Reduces water holding capacity when added to another media
  • Allows for more frequent irrigations
  • Less likely to over water
  • Chemically inert
  • Stable Ph

Clay pebbles are the underrated hero of hydroponic substrates. They are one of the most commonly used amendments to pure coco coir potting mixes due to the fantastic aeration properties they have. One of the most common user errors when growing with coco (especially for the first time) is over watering. The addition of clay pebbles makes this a problem of the past, as it instantly reduces the overall water holding capacity of your pot and drastically increases its drainage capabilities. This allows you to irrigate your plants more frequently, allowing you greater control over the EC and pH of the substrate.

They should not simply be looked at in terms of just being suitable as an amendment either. Clay pebbles make for a fantastic substrate purely on their own. Highly suitable for flood and drain systems, or even drip irrigation systems, they allow for a much more frequent irrigation regime while maintaining an extremely high level of aeration for a developing rootzone. Either way you use choose to use clay pebbles, either on their own or as part of a potting mix, they are a truly fantastic addition to any hydroponic grow room.

Hydroponic clay pebbles are available in either a 10 or a 45 litre bag.


The clue is in the title. Clay pebbles are exactly what they say on the tin: small little pebbles made from expanded clay. The word expanded being quite important, they are not solid little pebbles of clay, but also possess more of a porous nature from their honeycomb like composition. The high temperatures during the production process cause the clay balls to expand, much like cornels when you are making popcorn. This produces a high number of micro-pores within each clay pebble, increasing their potential for storing water, oxygen and nutrients.

There are many different sizes and shapes of clay pebbles, from perfectly spherical balls to irregular chunks, each one with its set of positives and negatives. We make sure we source only the finest and cleanest grade of clay pebbles, taking all the guesswork out of it for you. The pebbles we stock are 100% suitable for agricultural use, with no background heavy metal content, meaning you have the best chances of securing yourself a high-quality crop! 


Growing hydroponically is all about using a media that will supply the roots with a higher level of oxygen, while providing an adequate supply of nutrients and water in a more efficient way for the plant. The air pockets in between each clay pebble and the micro pores within each pebble themselves means that there is always an extremely high level of oxygen available to the roots. The higher the level of available oxygen in a pot, means the higher the potential for nutrient uptake by the plant.

It is not simply down to the increased level of oxygen in the pot though, the way in which a media physically holds on to water also drastically effects how a plant will grow. The simple act of taking the water from the substrate by the root is extremely significant and most of the time, completely overlooked. Each type of media will hold onto its water content with a different level of force. Peat based mixes, for example, generally require a higher amount of force from the roots to take up the same amount of water when compared to hydroponic media. The force required to take the same volume of water from clay pebbles is much less, meaning the plant has more energy left over to put into production of flowers – meaning a potentially bigger yield!

Clay Pebbles are classed as an inert growing media. This means that they contain no available nutrient in the way that a pre-mixed potting soil does. This means that the level of feed (EC level) you use on each irrigation is what is available to the plant, so it is crucial to make sure you get it right! You need to be monitoring and keeping on top of your EC and pH levels a lot more than you would do with a media that is not inert, otherwise you will not get the most out of your plants – you are fully in control of your plants!


Although clay pebbles are washed in the factory, it is always a good idea to wash and treat your pebbles after purchase. Firstly, with washing them, you want to make sure as much of the clay dust/sediment is removed as possible before potting-up into your hydroponic system. During transport the pebbles will always generate dust simply through movement, so you need to wash as much of this off as possible beforehand. Piercing holes in the bottom of the bag and running a hose through is one of the simplest ways to clean individual bags. For larger volumes of clay pebbles, it is easier to wash and drain them in a larger container all at once.

After they have been washed it is best practice to treat the clay pebbles to get the pH and EC to the correct starting point for planting out into. In particular, the pH of clay pebbles is typically quite high, so it is a good idea to soak them in a slightly lower pH solution to compensate for this and balance it out to a pH of around 5.7-5.8. If you have a flood and drain system this can be done after washing, when they have been put into the pots. Simply set the reservoir to the appropriate pH and EC levels, then keeping flooding and draining until the pH and the EC have stabilised in the reservoir. Once the pH and the EC have been set you are good to go!

Clay pebbles can be used highly efficiently as a standalone substrate, but you will need an automated irrigation system to do so. Typically, the most suitable systems for using pure clay pebbles as your hydroponic growth media are either continual pot based drip systems, or flood and drain systems such as the IWS. Without an automated system it is not advisable to make use of pure clay pebbles, as you will not be able to maintain the amount of irrigations necessary.

Alternatively, clay pebbles can be used as an amendment to a soil or a coco coir substrate where you think you may benefit from extra aeration, drainage or a lower water holding capacity in the pot. This allows you to have more control over the conditions inside the pot as it gives you the opportunity to irrigate more frequently. This is also highly beneficial for systems where the pots will have continuous access to water, in systems such as Autopots, to avoid any problems associated with overwatering.

 Lastly, clay pebbles work fantastically well as a mulch, covering the top of the substrate in your pot. This helps to avoid excess surface evaporation and helps to prevent against any pot dwelling nasties such as fungus gnats.


Clay pebbles can easily be re-used, simply soak in a solution of hydrogen peroxide to get rid of any old root material, then repeat the washing and buffering process that you would normally do after buying a new bag.

It is ideal to root a plant into a rockwool block before going into clay pebbles. A 3” or 4” cube makes the perfect starting point for a healthy root zone to then be planted directly into clay pebbles. Make sure the bottom of the block is sat almost dead on with the flooded water level, to ensure it does not become too wet or too dry between irrigations.

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Richard J.
United Kingdom United Kingdom
Clay pebbles

As advertised - quick delivery - up on my green roof now!

Robert S.
United Kingdom United Kingdom
Washing ****!

First off, I'd like to express my gratitude to GroWorks for their prompt dispatch considering the current situation we all find ourselves in. This was first experience with clay pebbles. I had read how important it was to wash them and then wash them again. I would like to qualify that with .... again and again and again! If anyone comes up with a pre-washed version, I'd be in like a shot! As I'm unable to compare this particular brand with any other I can't really express an objective opinion as far as quality is concerned. Having said that, they are in their pots doing their thing and all seems well. I would have no problem buying them again when needed (unless a pre-washed version catches my eye)!

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Clay Pebbles

Clay Pebbles