Expanded clay pebbles for hydroponic grow medium

Expanded clay pebbles

Clay pebbles or hydroton are made out of mineral products that are heated in high temperatures until they pop and take the form of oddly shaped, semi-rounded pieces of clay-colored popcorn. Expanded clay pebbles has become one of the most popular growing mediums offering multiple benefits to gardeners. This article provides a good basis as to why you should pick this medium and how you can extract the benefits.

What are expanded clay pebbles?
When clay pebbles are exposed to extreme heat, they pop and expand, and you end up with this very light weight clay pebble that is great for growing plants in. Other growing mediums include perlite or Rockwool.

Why pick expanded clay pebbles over others?

Expanded clay pebbles are really easy to work with and especially useful for small applications. The shape and form of expanded clay pebbles makes a good medium for because it allows you to easily put your hands down in your growing medium to take out plants. It has a good water holding capacity, not huge, but still better than other types of plant medium. Surface area is one of the essential properties of growing mediums. The

Things to note

Once you start using them they will have a lot of air which makes them float

As they saturate water they will stop floating and become more useful. The growing medium is especially good when used with ebb and flow or flood and drain type of production systems. When the clay pebbles stacks up and forms the grow medium, there will remain a lot of air inbetween each clay pebbles and inside. This is good because as water drains away, you have left a lot of oxygen and air circulating the root zone. It is good

Summary of pros and cons


  • Easy to work with
  • Great to put in plants and taking it out
  • Biological surface area – good colonization by your microbes
  • Renable, doesn’t take much to make cus we are dealing with mineral, low pollution


  • Pretty expensive
  • Tends to float on the front end
  • Can cause problems with pumps and plumbing, cus they float up to begin with, there is risk that some of the smaller pebbles float up, gets sucked in to pumps or pipes,
  • Dusty, rinse before getting into system

Additional recommendations:

Water level:

Appropriate water level for a clay pebbles system So roots don’t rot

Usually an inch or so below the top of the clay pebbles to keep algae from growing or the cultivation of gnats

Because clay pebbles are very poruous and well aerated, users can experience some plant types to dry out quite fast. Avoid using them for plants that like their roots kept constantly moist, like peace, lilies or crotons. But if you mix with normal soil on atleast 50/50 ratio then plants can still gain nutrients. If you fertilize plants constantly, then there isn’t really nee for 100% pebbles potting.

Properties in media

PH is the biggest concern

After that surface area for bacteria and an ability to retain a bit of water

Expanded clay is good but expensive

Alternative – gravel – but before buying a whole truck, get a sample and check if it alters the ph of water after sitting in it a week or two. If stones have calcium etc it will change the ph pretty drastically. A quicker way is to put a handful into a glass of vinegar, if the liquid starts to bubble after few minutes, then you know it will affect the ph.

bigger the surface area the better capacity for retaining water and bacteria. If you combine this with organic matter you can increase the water hold up.

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