Root Health - Rockwool vs Perlite

omerizm · #1 07-25-2010, 05:28 PM

I have different types of lettuce growing in my DIY NFT system. As a medium, I used rockwool cubes and cups filled with perlite.

The roots of those grown in rockwool cubes don't look healty. The part that remains above the solution is yellow. Down below, the part that is in contact with the solution is white.

The roots of those grown in perlite filled cups seem to be ok. They are all white. Note that the cups are suspended above the water level as well, so the upper part of the roots are not in contact with the solution.

Please see photos below.

What is the reason of this? Should I let the rockwool cubes sit on the bottom of the gully?

GpsFrontier · #2 07-25-2010, 08:09 PM

Is this a flood and drain system, or NFT system? I'm not sure if anything is really wrong, some root discoloration (yellow, or light brown) is not necessarily bad. But is usually either on older roots, or roots stained by the color of the nutrients. Although from the pictures it looks like the plants in the cups hang down farther. That is ,that the bottom of the rockwool cubes is higher than the bottom of the cups. Therefore it's not nearly as noticeable on the plants in the cups, simply because their roots are closer to the water level.

P.S. Just curious, is that vinyl fence post tubing? I'm needing some 4 inch square tubing, but vinyl fence post tubing is too expensive for what I need to do.

omerizm · #3 07-26-2010, 03:54 AM

It is an NFT system. It is true that the plants in the cups sit closer to the water. All Plants seem to be ok for now, the leaves look good and they are growing. I just want to understand why this is happening. The difference is really obvious.

The gullies are 2.8 inches deep. The rockwool cube is 1.5 inches. So it is suspended high. It is not moist. Is this ok? Should it sit at the bottom of the gully? How can I do it?

I used rectengular rain water pipes that are used to run the collected water from the roof the the ground. They are 2.8 inches high, 4 inches wide and 13.1 Feet long, made of PVC.

Köşeli İniş Borusu - Ege Plast - Plastik Boru

GpsFrontier · #4 07-26-2010, 05:42 AM

The discoloration is just due to being exposed to the air, because that part of the roots are continuously exposed to the air, and there is probably a lack of humidity in the tube that would keep that part of the root moist. The rockwool shouldn't be dry, but it shouldn't be soaked either, just moist. The roots are not wicking up enough water to keep it moist. If the plants are doing OK, then I don't know if there is any real problem. But If you want to try and lower the rockwool cubes that would help get more moisture to that part of the root system, and hopefully wick up some moisture into the rockwool cubes.

Going by the pictures, I think the easiest way to lower the rockwool cubes is to simply use the same white cups you are using for the other plants, then cut holes in the bottoms of them to place the rockwool cubes into. Personally I would experiment and make some low enough that the cubes just touched the water, and some that were just above the water level. I have seen setups that the cubes were sitting on the bottom (in the flow of water), but that will constantly saturate the rockwool cubes with water. But either way they will probably do fine. Now that I think about it, I don't think lettuce plants mind wet feet much.

P.S. Thanks for the info on the tubing, they looked square in the pictures. The rectangular rain gutter downspouts are common and easy to get here also, although for the design I have in mind I need true square 4x4 tubing or it wont work. I have found square rain gutter downspout tubing, but unfortunately not 4 inch wide.

Anianna · #5 07-27-2010, 12:05 AM

GpsFrontier, just thinking out loud here since this isn't something I have actually tried, but I know some crafters who build molds with plywood and nails and then heat pvc with a heat gun, bending it into the shape of the mold. Perhaps you could use 2x4s to press a round pipe to square it. It would probably take a lot of pressure and I would think the corners would be somewhat rounded. I'm not sure if that would suit your needs, but it might be something to try.

GpsFrontier · #6 07-27-2010, 02:52 AM

Quote:

Originally Posted by Anianna

GpsFrontier, just thinking out loud here since this isn't something I have actually tried, but I know some crafters who build molds with plywood and nails and then heat pvc with a heat gun, bending it into the shape of the mold. Perhaps you could use 2x4s to press a round pipe to square it. It would probably take a lot of pressure and I would think the corners would be somewhat rounded. I'm not sure if that would suit your needs, but it might be something to try.

Thanks for the thoughts Anianna, that is a possibility although it would be quite an involved process to do right, and costly I'm sure. The design is for 20, 10 foot long tubes. I would need to build a press that would shape it, then find a way to heat the whole tube at the same time to the right temp, in order to re-mold it without melting it. I would also need to do some trial and error to fine tune it I'm sure. Then comes the hard part. I also need 40 end caps for the tubing. As well as about 20 couplers to connect more than one piece of tubing to another, in order for easy disconnecting for cleaning and maintenance, depending on if I can get the end caps to very tight, not just water tight but resist yanking and pulling (yet removable).

P.S. Just to give you an idea what I am planing I attached a couple of pictures of a small scale setup of the design. I designed the small scale system to hold 4, 5-6 foot square tubes (holds 64 plants). I plan the large scale project to have 20, 10-12 foot long tubes (depending on the length of the tubes I can get), that system should hold a minimum of 640 plants (likely about 700). The vinyl fence post tubing would run me about $1000 to do ($650+tax for just tubing, then I need end caps and couplers). But to keep on budget, I need the cost to under $500 total.