A Community and Forum For Aquaponic Gardeners

Media Question

I just scored a few pickup truck loads of free red lava rock. I was planning on using it for my flood and drain media beds and general landscaping. My question is most of the rock is pea sized to 3" or 4" and I have read where 1/2" to 3/4" is used in AP systems. Can I use slightly larger rocks in my Grow Beds? Or can I use larger rocks in the bottom and smaller rocks in the top 6" or so? I am not sure why the smaller rocks are used when it appears that the larger rocks create more air/root space for the plants? May be a dumb question but I am hoping to cut my sifting/rock sorting time down. I did pour some vinegar on the rocks and they appear to not fizz at all. I will buy a PH test kit and do a test before using them in the AP setup. I figure worst case scenario, they will look good around the outside of my grow beds. Thanks!

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Permalink Reply by TCLynx on April 9, 2011 at 5:21pm

Lava rock is a good media (it's what our friends in OZ call scoria) the only exception to that would be if it was used to filter industrial waste so make sure it didn't come from some place that was using it for industrial purposes.

I've used plenty of the larger lava rock in the bottoms of grow beds and around the drain gravel guards. Smaller media up on the surface can help hold seeds in place while larger rock might just let the seeds fall down to the bottom of the grow beds. Smaller media for the surface layers will also block more light from getting at the bacteria and plant roots.

Permalink Reply by David Owens on April 9, 2011 at 5:50pm

Thanks for the info TCLynx! I thought this may be a good question to share with all of the other newbies in the community and now I can work on the sorting a bit less! :) The owner told me he bought it from a landscape nursery and it was in his back yard for 10+ years so I hope it will be OK

My back thanks you!

Permalink Reply by TCLynx on April 9, 2011 at 6:03pm

Lava rock has some great surface area for bacteria to grow in and it is commonly used for filters in ornamental and koi ponds.