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grodan rock wool - how small can I get away with for seedling

Posted by jackblasto none (My Page) on
Sun, Jan 19, 14 at 20:56

I've started quite a bit of lettuce in small 1" grodan cubes, moving them to clay pebbles in a flood and drain hydro setup for a few weeks now. All of it doing well. In an effort to conserve rock wool I have a Question. COULD I cut these grodan cubes down in half for the seedlings to conserve rock wool since their real home once started is clay pebbles? Meaning, how intensive of a substrate does a head of lettuce need for start up, since once it's a baby plant I am moving it to the clay pebbles (within 10 days). Could I cut the 1" grodan cube into a 1/2" cube, a 1/4 inch cube, etc? What is too small that it would detriment it's beginning?


Follow-Up Postings:

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RE: grodan rock wool - how small can I get away with for seedling

We use 1 in cubes and fill in around them with clay. I wouldn't go smaller than that if you plan to transplant them. But you can give it a shot that's how I have learned most of what works for me.


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RE: grodan rock wool - how small can I get away with for seedling

I have to agree with Rio_Grnade however i understand your thinking. Even after taking out some of my plants (after harvest) you could not tell there was ever a grodan cube. I will say Grodan sent me a bag of their chunks that worked great. I used an egg carton and then sprinkled seeds over them. I had seedlings growing in just one tiny chunk. So it can be done, but what i found out was in the TEXAS HEAT if i didn't keep an eye on the smaller chunks with seedlings in them would start to dry out. So i would just scoop out a spoon full of the chunks and put them in the net pots then cover them with clay. I really like the Grodan Cubes, However my attempt of a third set of transplants isn't working for me. I have them in dome with a little heat mat. The first two time i just set them under my gazebo in Aug and they took care of themselves. Sorry Off Subject....


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RE: grodan rock wool - how small can I get away with for seedling

The cubes are 10 cents each.

What am I missing? You can't be growing hydro to save money, right?


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RE: grodan rock wool - how small can I get away with for seedling

Part of what's important, is the support that the rockwool gives? Because if I wanted to do away with rockwool, I would just experiment putting them directly in hydroton if space weren't a problem.

Maybe experiment presoaking the ungerminated seeds a day or two in water immediately before or using a very small percent peroxide water, or even in something like orange juice first spotty/slow/low% germination were a problem.

I am thinking the smaller the rockwool, the smaller the roots, so this would just be checking the other extreme eliminating rockwool completely. Generally, I think the question of minimum rockwool size is specific to your setup design, ambient conditions and watering frequency, so what works for one might not work for another.


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RE: grodan rock wool - how small can I get away with for seedling

I grow everything in hydroton, so I can water more consistently , I found that using rockwool it was very easy to over water the plants,, so I have taken the path of least resistance using expanded clay , with the drip system, ebb and flow system even using the Kratky method.
I grew a Japanese leafy vegetable called Katasuna using the Kratky method in hydroton which grew beautifully, I gave some seedlings at the same time to a Japanese friend who planted in soil and are only 1/3 the size of the ones I just harvested.
I know many use rockwool and even the Canna coco peat successfully, I guess I am lazy, however my growth rates are very good, too old to change my habits while I am getting great results.


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RE: grodan rock wool - how small can I get away with for seedling

I don't use any rock wool at all. I place the seeds in a very small piece of paper towel. .25 x .5 in and place it about a half inch into a 2 inch net cup with hydroton. Place them in a home made bubble bucket or similar container and bring the water level to 1 inch of the net cup like a DWC system. Let the air stone run and just the moisture escaping from then net cups is enough to germinate the seed and draw the roots down until you are ready to put it into a different system or let them grow out in there.


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RE: grodan rock wool - how small can I get away with for seedling

hyrdoboy: Does this work in the winter? My second round of winter seeds just didn't work germinate I didn't have a heat mat but i did use some Christmas lights under the tray for heat. I did everything the same as i had in August but very few of the seeds sprouted. Austin is having some crazy weather. Any thoughts on seed germination would be appreciated.


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RE: grodan rock wool - how small can I get away with for seedling

"The cubes are 10 cents each.
What am I missing? You can't be growing hydro to save money, right?"

haha... point taken


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RE: grodan rock wool - how small can I get away with for seedling

I have had success with sizes as small as 1/8th of a cube(1/2"x1/2"x1/2"). I've also had a lot of failures, in all sizes. I found that with rock wool there was too fine a line between drowning my seedlings with too much water and having them dry out, wilt and die-off overnight.

I am/was starting plants to grow in either an NFT system or an ebb and flow system with hydroton as a medium and I ended up using a system something like hydroboy's, except my 2 inch pots are suspended in a raft of 2 inch Styrofoam. I like the air stone Idea and I think it would likely allow the plants to grow larger roots before moving.

Do I have an extra air pump lying around..?


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