Beginner choosing media

[Louise]

Hi!

I'm currently building my first aquaponic system, and will be pesting you with questions for a while.

My grow bed will be approximately 2 meters by 60 cm, and 27 cm deep (6½ foot x 2 foot x 1 foot)

That means I need 300 litres of media.It will be a flood-and-drain system.

I happen to have a big bag of crushed lava (leftover from a roof gardening job), which will probably be enough. It's rust-brown lava gravel, sizes 5-15 mm, approximately (1/5 inch - 3/5 inch).

At the current roof garden job, we also use LECA (Hydroton) by the truckload, so I could probably get a bag of that too, for a small, or no, sum.

Which one of these would be to prefer?

I saw the thread on hydroton floating, and that has also been a concern for me. So, I gather the solution is not to flood the beds more than to an inch or two below the surface. But how do you sow? You must have some little pots with a finer media, I assume, but how do you get the seedlings watered before they get roots long enough to get two inches down in the media?

Louise

[Scott Westhoff]

Yes, don't fill your bed above that level and hydroton is a good choice.  Either will work, though.

There are many ways to sow the grow beds.  You can sow directly onto the grow medium and it will work its way down to the water.  I prefer to start plants elsewhere and then transplant them.  You can use the grade school trick and start the seeds in a plastic bag with a wet paper towel in it.  Once the root is long enough (about one inch), you transplant it.  Of course you can start the seeds in soil and then wash the roots before transplanting into your system.  Rockwool is another option.  It is used for hydroponics.  You just get it wet and then sow a few seeds in each cube.  Once the plants sprout, you can place the cube in your AP system.  

[Louise]

How about people who use worms in their beds - what do worms feel about hydroton? The LECA I have acess to is 12 - 20 mm large (½ inch to almost 1 inch). It seems too big for seeds, and not really comfortable to worms, or do they care?

The crushed lava I have are sort of sharp bits, but not very.

I'm thinking maybe I'll try the lava gravel in this first bed. But I'll want to experiment with other things too, later.

[Scott Westhoff]

Sounds like a good idea to experiment.  The worms don't care. They can be used in any medium.  I think the roots will grow through the rocks just fine.  The rocks won't be moving that much.  You can use a combination of both medias.  

[Louise]

I looked at my bag of lava gravel today, and it seemed I had less than I remembered, though I'll know for sure when the snow is gone. So it looks like I might be mixing after all. Question is whether to try and layer the different media, mix them completely, or divide the growbed lengthwise or crosswise, or something.

[Scott Westhoff]

Put the smaller material on top.  It will fill in the cracks left by the bigger stuff.