As I understand it the point of using porous materials is not to increase/decrease water retention on the outside of the particles, but to provide sufficiently large pores to allow air circulation around the roots while still providing enough humidity (from water stored in the inner pores) to help the fine roots to stay alive. That's the point of using products like Turface or Floor Dry. I'm just wondering if pumice is really in the same category. If you look at xerophyte nyc's experiment here, you'll see that a similar substrate, lava rock, holds very little water. (Thank you for that, xero!) The pores in volcanic rock may be so poor at storing water as to make these substrates comparable to granite, a substrate used for its minimal water retention.

hello this forum mayb closed i am looking for only natural and organic growing mediums, i have used lava rock on and of since about 1983, the first time i used it right as it came from the bag that lasted till about 88, i got some free time on my hands and i pulverized my lava it was about 2 - 5 gal buckets worth when i gave up i still have that batch i just rinse it well if i want to use it i have had real good luck just using it as a normal water as needed medium, our thinking was such great things come from the islands and had seen the great flowers there , pinapples come from there so,,, why not grow in it as long as i keep it well drained and no obstructions on the drain holes it has been some good medium, but i never really had much time to actualy set up a real hydroponics system like u see now days it was just ur bare knuckles pump the water in and cover the medium and drain it out well, since then i have been tryn to utilize some water and slopes and grow fish and plants in our ponds and i have ignored lava rock till the last few yrs but now i am really looking into growing only organic in truly only organic containers and anything touching the water and its been very tricky since my wife does cancer treatments and my background is environmental i have looked at cancers and sickness as a result of what we eat and whats in all of what we digest and the containers that touch it and what its grown in and watered with,,, so,, my point? i have used lava rock but consider it somewhat inert but with my chemistry background and knowing whats in all the water and whats gonna be in the fish excretions from gills and excrement's it will have some affect on anything in lava rock that might dissolve up to the point my fish algae coats it with that slim, so my concern? i saw one blog where the blogger says lava rock gives off dangerous chemicals ,,, but its blog to me seemed to b pushing claycorn ,,yet its man made from who knows what and is imported from china i also see that it starts out and may stay with a p h of 8 my lava rock in and 7 ph filtered tap thru 3 charcoal filters shows 8 depending on whose eyes u use, ,,i see where the most fertile lands on earth are in volcanic soil but upon checking cancer rates in these areas i find that many say they have high thyroid cancers in those areas of course the people are exposed to more than the soil yet i found a very few isolated volcanic areas where no cancer existed but they say its from the general diet high in certain elements,, since lava rock numbers i have seen imply 66% silica, 16% aluminum. 10% iron,, lists only 10 total elements i am wondering if i should be concerned with the aluminum, and its possible affects on humans causing dementia, n Alzheimer and no i do not want to hear its a metal and it will not react i am talking pure submersion in my fish ponds and in my grow beds ,, i have stayed with what i think is river rock for now since thats what i ve always used for fish, (and its probly all conglomerate of marble (igneous limestone), granite, quartz, limestone, with one pebble or 2 or lava rock) but since i am planning on eating the fish and i am tryn to remove all man made items such as plastics, vinyls, pond liners, additives in my fish food and meds and hormones not used and all fish treatments removed ( if they die they get blended for chum), are there any other obsessive people who can give me any reason to not use lava rock over man made clay balls for grow medium my brother n law is sure that the clay balls have been developed by the professionals, my son who is helping with the learning is too young to do anything except as what the hell are ur talking about old man? i have not finalized my choices but i see the professionals as only there to part me with my money and sell me some snake oil when it comes to clay made pellets, ,, so do i have to worry about the aluminum, or any of the other 7 items aside from the silica i know i should not breath when i pound it to a pulp, i am tryn to be as true and pure organic as can knownly be and growing inside greenhouses and enclosed ponds not sure how i m gonna get the birth control pills outs the water if its not truly well water but has been slipped in from the lake if my charcoal filters won t remove it except to maybe us my springs that have p h of 6 and drill my own well, of course when i add the wrong things to drop the ph it actually draws out more of my alkalies but i have probly always grown my crops in a ten due to growing in this east texas iron ore and sand , and in central texas dirt and here i have always added gypsum to cancel out the chlorine added to the tap water if you can sort this out and it gets past censors please let me no if anyone out there can shed some lite on my determination to use all lava rock and river rock and white marble or limestone rock

Hey Atheen... Perlite, also called sponge rock, is mined, crushed and heated to between 1,500 and 2,000 degrees Fahrenheit to make it lightweight and porous. This siliceous rock is mined worldwide, but the U.S. is both the largest producer and consumer of perlite. Pumice results when tiny gas bubbles are trapped in volcanic lava before the lava cools, resulting in a naturally lightweight rock. Most pumice used in the U.S. comes from Oregon. Perlite is lighter weight than pumice and lighter in color. It is pure white. In soil mixes, perlite tends to float to the top of the soil, spilling over the edge of a pot when watered. It usually costs less than pumice and is manufactured in different grades, weighing as little as 2 pounds per cubic foot. It is chemically inert, has a pH of about 7 and provides no nutrients to plants. It does not compress, so the drainage it provides is permanent. Pumice, formed from molten lava that cools quickly, is porous, letting water drain through it. It is usually a dusty white or pale gray, but, depending on the minerals in the area where it is mined, it also can be pale yellow. The Latin word “pumex,” from which the name pumice is derived, means “foam.” Pumice contains tiny bubbles of air, and it floats in water, but not nearly to the extent perlite does. Pumice is not processed beyond being sorted by size. As you can see, pumice holds more air spaces, weighs more which helps anchor plants, especially taller ones, and allows more nutrients to hold to the surface verses perlite..I love pumice

Yan I use grit, perlite (in equal amounts) and less turface. Your mix sounds good using what you have available. I believe that you could adjust water retention as needed by using more or less of coco coir. Most important is to find if there is any water retention deeper in the pot - it may, or may not be. Not sure how you tell, but using a wooden stick (bamboo chopstick or skewer or dowel or even pencil) stuck deep inside the pot can give you idea. Once you know for sure, you can water more or less often. Even filling empty, see-thru container (with drainage holes poked in) will give you great picture: you can watch as you saturate the mix, how fast it dries up.I hardly ever fertilize, since most of the water my plants receive is from rain. On rare occasions I have to water, it is same fert I use for my veggie and flower garden (soluble MG 24-8-16 or liquid 12-4-8 which is the same proportions).