Pumice stone -- size about the same as your little finger nail , and yes it will absorb and hold water after time and it will release oxygen as well , my thought on this idea was to increase the amount of oxygen to the roots as well as having good drainage . The pots have 10 ml holes all around the outside , I made my own pots . So I am thinking that once they get to the edge of the pots they will air prune and the roots in the pumice will have a good supply of oxygen , so far the best lay out is with the THC Bomb I have growing , I can run 1 1/2 ltr every 2 days though it and no water logging , which I believe means the plant can get more oxygen ? The pot with the THC Bomb has a core of dirt in it , this I like better . I am just about to start a outdoor photo grow and have made up a 200 odd ltr pot to try . Now I have no science behind this , it is just what I observe . I have not taken a plant to a full grow yet but I am liking it at this stage . just found this .-----
The cultivation of non-soil is a pioneering method of production in greenhouses, as the producer avoids the use of pesticides, substances with effects on health and the environment in order to disinfect the soil. According to this method of cultivation, the plants do not grow in a natural soil, but they grow in pumice (substrate) in which fertilizers have been added in appropriate quantities. In this way, the spread of pathogens that causes soil-borne diseases is avoided. No chemical disinfectants are used for their treatment , as well as no chemicals are used for the control of weeds. Therefore, the use of pesticides is significantly reduced and it is kept to those which are not toxic to humans and are degraded very quickly in nature.
LAVA pumice stone, the unique natural substrate, has excellent performance as a horticultural growing medium, considering that it is free of plant diseases, features a balanced ratio of water capacity to air permeability and it does not impact the environment at the end of its lifecycle. Furthermore, LAVA pumice stone adequately reconciles water retention needs with proper root drainage and aeration requirements.
LAVA pumice stone is perfectly suitable for soilless cultivations of tomato, cucumber, pepper, rose, gerbera, gypsophila, carnation, chrysanthemum and other vegetables and flowers. For all these reasons, pumice stone has become a very interesting substrate for hydroponic cultures, both in Greece and abroad.
LAVA pumice stone is a domestic natural material with no chemical fermantation thus, compared to other imported or non-imported substrates or soil improvers, its production and transportation costs are significantly lower. Moreover, LAVA pumice stone can be re-used in cultures over long periods of time (up to 6 years).