E-mail - Rockwool and Seedlings

Hello Dr. Myers,

I’m using Rockwool so should I tease the Rockwool so that its covering the top of the seeds and just let the seeds push their way through or should i just leave the seeds uncovered inside of the propagation tray with the dome

I have written about Rockwool in general in a previous post about hydroponic mediums. Rockwool can hold large quantities of water and air which aids root growth and nutrient uptake. So, if it is sitting in water it should be able to keep the seeds wet enough to force germination if the seeds are just on top of the Rockwool. (See warning about seedlings and standing water below) The seeds could be put in the little holes in the cubes and left to come up on their own if they are the size of apple seeds or larger. Smaller seed could just be put on top of the Rockwool. As I have said, Rockwool is used principally in hydroponics.  However, I used to start the seeds in a tray in Rockwool cubes and then put the cubes in soil. The Rockwool like the coir plugs I use today just made it easy and mess free to start seeds. The nice thing about Rockwool is its fibrous nature also provides a good mechanical structure to hold the plant.

Hey Doc,
If I had a seedling in a Rockwool cube that I transplanted into a flood and drain system using hydroton what level should the water come to in relation to the Rockwool? Should the water line come just below the Rockwool?

Perry a manager at HTGSupply.com gave me some info. for this post since I have not used this type of system. With Rockwool, you could either have it flood and drain, or have the cubes constantly touching/sitting in water. If you have small seedlings then you may want to flood and drain because the cubes could be too saturated when sitting in water and cause root rot.
Many seedlings are just are too small to pull air into the Rockwool (it will be very saturated in standing water) but after a couple sets of true leaves most plants will be big enough to pull air into the cubes even if the cubes are sitting in water.

Good Growing,
Dr. E.R. Myers