Need help deciding on materials for passive hydroponic system

Hey! I've been growing plants in soil for a long time and am finishing up my first cannabis grow right now in soil. However I've built a new stealth grow cabinet and hydroponics is definitelythey way I want to go. I'm growing autoflowers.

The containers I bought are 10" tall 7quart rectangular waste bins. I will be growing 6 plants one in each waste bin. Originaly I was going to go with the hempy bucket but as I am VERY low on cash I'd like to find a media that won't cost as much (2 gallon bags cost $6 here, that's $36, I'm poor!)

I live in a volcanic area, there are tons of cinders everywhere, I'd have an unlimited supply. By cinders I'm talking about the red lava rock. What I want to know is, how can I use lava rock to make a passive system?

Is lava rock an ok replacment in the hempy for perlite? 70/30 lava verm?

How about using lava rock in a 70/30 ratio to coco coir? it seems like this may work but I've been reading about people having problems with coco.

Any other ideas for a very cheap or free media? The lava rock is all sizes, I'm guessing the small stuff is best. Its heavier than perlite. I'm not sure how they differ in behavior.

Thanks!

if this lava rock is porous and absorbs water, it's definitely worth the try. have you considered rockwool cubes? they're hand watered should not be kept soaking wet very good for a passive system imo

Grew 150 "007" plants in Lava rock last year. I just placed my cloned plant in a 3.5" cube. Then placed on top of 8" pots filled with just lava rock. Each pot sat in a drainage troth and recycled back to reservoir. The roots took right off deep into the rock and very dense. Just dont move the pot! The rocks are sharp and can cut your roots easily.... Had no PH problems after running for a week. Once the dusty bits flowed out of the rock. Used a drip feed system at 2gph into the cube.
Regards..

rockwool sounds like it maybe a little expensive in the amounts that i would need, though i will continue to look into it. thank you so much for your reply!

The lava rock is very porous, i put some in a cup today, watered it from the top so there was an inch of water on the bottom. after 3 hours the rocks were all still wet and after 5 hours only the top ones had dried. im not sure how well these wick water compared to perlite but it seems to be doing good.

i think if i use small rocks mixed 2:1 (or 1:1?) with vermiculite or coco there should be plenty of water retention as well as plenty of air and good drainage.

if anyone has experience with such a mix please let me know. I started a bunch of tobacco seeds yesterday to try out on the lava rock, dont want to buy the verm or coco until i know its alright to use.

thanks everyone!

heh we posted at the same time. so lava rock works no problem for constant flow systems, thats very good news. unfortunately my setup has no room for a reservoir and i cant buy 6 different pumps (designing grow for a perpetual harvest, staggering the plants starting times).

Is the rock sharp enough that any movement of the pot can be detrimental? ill be doing lst as well as some breading so they will be moved some. if im careful will it be ok? definitely no transplanting.

Yes I found out after moving some plants...lol. Well I was using the cheap soft plastic pots. So they flex quite a bit when handled. If your using more sturdy pots just fill em up and shake and drop pots repeatedly to settle the rock. 3.5" plastic sleeved RW
cubes are very cheap. But work great to start the plant and on to finish. I didnt even have to support my 4ft tall plants as the roots permeated the lava rock so well and cause of the weight of the rock. And yes... There were plenty of fans running trying to blow
them over. lol

Awesome, thanks for the help! Lava rock is what I'm going with. I run test plants - tobacco and lions tail so that when I grow the herb Its not my first time with the setup.

Coco sounds like it messes with nutrients and salts etc. I'm going to make the mix lava rock and verm. I have a lot of experience working with verm so ill use it at 50% down to 30%.

Now I just have to decide on a nutrient to use and... Purchase it.

Your welcome ! No get cracken !! lol