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September 08, 2022

Hydroton: What are those clay pebbles everyone talks about?

Hydroton is one of the most functional and sustainable plant growth media on the market.  It is also called lightweight expanded clay aggregate (LECA for short) and clay pebbles.  This growing media is used for gardening in hydroponics, for houseplant decoration and for better drainage in soil. Hydroton is the original brand and manufacturer but has spawned various other brands and names, such as Grow !t Clay Pebbles.  LECA’s history and uses date back long before its use in Hydroponics. It was initially designed in the 1930s for use in building materials, likeconcrete. To make LECA, natural and unprocessed clay matter is cut into small pieces and placed in a rotary kiln heated to about 2000℉. Inside the kiln, gasses trapped inside the clay begin to expand, which result in air pockets that are baked into the mostly round shaped clay pebbles that we know and love as Hydroton. 


When used in hydroponic and aquaponic gardening, clay pebbles are typically added to a net cup or pot to provide structure and support for young plants’ root systems.  Although the hard consistency of this growing media may seem off putting or less than ideal for gardening, LECA’s pH neutrality and resistance to nutrient leaching provide a conducive substrate for root growth and development.  In addition, its lightweight nature means that, given enough space in a net pot or flood/drain table, it easily shifts to accommodate root growth. The space between pebbles allows oxygen to reach the roots, which is an important factor for preventing root rot.Root Rot, a broad term used to describe a number of ailments affecting a plants root system, is typically caused by overly moist soil or, more precisely, over-saturation of the plants root system which typically causes necrosis of the roots.  Nestling the base of a plant in LECA helps aerate the roots to help prevent this condition. Additionally, because the pebbles are porous and generally about 0.25” - 1” in diameter, clogging pumps with coco, soil, other grow media or losing other media to erosion or wash-away is generally not a concern.

                                                       hydroton roots hydroponics net basket             

         Healthy root growth in hydroponic DWC bucket system using clay pebbles.

As with anything, there are a few drawbacks. Typically, seedlings should germinate prior to transplanting into LECA.  Although there are specialized methods for starting seeds directly in LECA, most growers first germinate seeds in a secondary substrates; the most common of which are:

  • Rapid Root Plugs,composted organic material bound together by plant-derived polymer where seeds germinate before transplanting the entire plug into LECA; or 
  • Rockwool cubes, molten rock spun into cotton candy-like fibers and then compressed into cubes, blocks, or slabs where seeds germinate before transplanting the entirety cube into either a larger rockwool cube or into LECA;
  • Coconut Coir, a pre-buffered and pH stabilized organic media used to germinate seeds before rinsing the seedling and its roots clean of organic matter, and then transplanting the clean roots and stem directly into LECA.

These germination methods are most commonly used until the seedlings develop true leaves and strong taproots for the LECA to securely hold the seedling. If using a smaller net cup or pot, the roots can become constricted by the pebbles which causes stress that can stunt the plant’s growth. Depending on the nutrients used, a buildup of salts can occur on top of the hydroton, which is less visually appealing, but ultimately causes no harm.

 

For many, sustainability is a major factor in the decision to grow soilless. Despite the high temperatures required to make LECA, its ability to be sanitized and reused almost endlessly, make it one of the most sustainable options on the market. This same feature makes it much cheaper in the long-term, despite the higher initial cost for purchase.  Recently, LECA was explored for use in soil management to provide aeration and drainage, nutrient filtration in aquaponics, and even for creating sustainable biofilms. In fact, according to  studies from the United States Department of Agriculture conducted by the University of Illinois, using LECA as a soil amendment can create better formulated container soil mixtures and, thus, cheaper plant production and higher quality crops.  What's more, LECA was also shown to  perform significantly better as a filtration substrate in aquaponics (a method of growing plants in fish tanks).

 

Whether you garden using hydroponics, aquaponics, or traditional soil methods, LECA is one of the most versatile items to keep in your garden toolbox. 

Author: 

Cody J. Brown, J.D. (SuperSaiyanHydroponics)

 


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