Ideal size for lava rock as grow media

[William Crain Jr.]

So I am setting up my first aquaponics system. I decided to use lava rock for the media. I got several bags for my local hardware store got them home and found out they have many larger rocks mixed with smaller rocks. Some are as large as 1". Will this cause problems for my system? Should I empty the grow bed and look for a different option? Let me know what you think... I was thinking about having the very top layer 3 or 4" of hydroton anyway...

[TCLynx]

The really large rocks are totally fine down in the lower reaches of the beds, the only time large rocks are kinda a problem is if they are on the surface it might make planting a bit more difficult but I expect you could eve manage that thought the topping off the bed with the hydroton is a common practice.  I'm a bit cheap for the hydroton so I just use nice river rock over the lava rock but river rock is heavy and you have to make sure it is quartz type rock and not mixed with limestone.

[Japan Aquaponics - アクアポニックス 日本]

Hi William,  we do exactly as you have noted above - we have lava rock for the bottom 8 inches or so, and then add a 2 or 3 inch layer of hydroton over the top.  1" lava rock is no problem at the bottom as TCL said.  This way works well for us and is a significantly cheaper alternative than 11 inches of hydroton!!

[Chris Smith]

I use a 3/8 inch screen to separate the large cinder from the small cinder. I use the large cinder on the bottom and the small cinder on top. The small cinder on top makes for much easier digging and planting. The large cinder on bottom helps drainage on the drain cycle.

[Japan Aquaponics - アクアポニックス 日本]

Is that just a standard plastic screen Chris?  Any issues with roots when harvesting?

[Brant Moore]

Do worms fare well in the big cinder zone?

[Japan Aquaponics - アクアポニックス 日本]

In our own beds worms do just fine in the big cinder zone.

[TCLynx]

JA, I don't think he leaves the screen in the bed, he uses the screen to sift the rocks so that he can separate the bigger rocks to put in the bottom of the bed and uses the smaller stuff on the top.

[Japan Aquaponics - アクアポニックス 日本]

Thanks TCL... given that Chris does a lot with Wicking Beds, I thought perhaps he was using that screening method to some degree in the media beds.  I wonder if it could work though if you have large lava rocks and the smaller hydroton.  We have noticed them mixing together over time, but this might be an option to keep them totally separate?

[TCLynx]

Personally I don't think it would be worth it to put a screen in the bed since I expect that roots would tangle into it and make it difficult to remove single large plants without distrubring the whole bed.  I mean is a little bit of mixing really a problem?

[Brant Moore]

To TCLynx's point, If the agg were to be screened for size twice, say a layer of 5/8' over the top of a layer of 1", the 5/8 functions a little like the screen. When plants are taken out, and you don't want to add the larger media that was pulled out with it back to the bed where it will be closer to the surface, replace that media (volume) with hydroton (or other small media). Is this workable?

[Japan Aquaponics - アクアポニックス 日本]

To be honest, the mixing is not too great if you are careful when you pull the plants out... it is just that it is of course the hydroton that gets shifted down to the bottom, and damn that stuff is expensive over here... at least 2 to 4 times the cost that you pay in the US, and so I don't want to lose it!   But in reality, it is not a big problem and I think it would take a number of years before  the bed would be completely mixed.  

.

The top layer of hydroton is really only a luxury and is not necessary... it is more comfortable to work in, but other than that, more often than not we use 1" lava rock for the entire growbed and it works absolutely fine.

[Chris Smith]

TC is correct, I use the screen strictly to size grade the media prior to placing into the grow bed. I do not use the screen in the beds during growing. My layers do not mix too much. When I pull plants with aggressive roots, like celery, I tend to leave the deeper roots in place so that the bigger rock on the bottom does not get pulled up. Any roots left behind are eaten up by the worms very quickly.