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Old 11-30-2018, 12:25 PM
Broseidon's Avatar
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Default Rockwool cubes for propagation question on rinsing and nutes

Hi fellow bros and brodettes,

I obtained some rockwool cubes (Grodan 4x4) that I wanted to try out for propagation, as many others suggested, since I had some recent issues with jiffy plugs.

Now to my 2 questions:

1) I read that you no longer need to rinse Grodan cubes because they changed their manufacturing process and the limestone residue from manufacturing that caused them to have a high PH, is no longer part of the equation. Meaning they no longer need to be rinsed with PH 5.5 water to bring overall PH down to ~6-6.5 ... Can anyone confirm this?

2) Since I grow all organic, rockwool cubes don't really fit into my overall setup and I have no bottled nutes on hand.
I want to use the RW cubes for propagation of seeds and cuttings only and then transplant into my regular organic soil mix when roots show.
But most people seem to suggest to soak them with a nutrient solution from the start.
I believe seeds can probably make due with just water in the RW cubes, as the seed contains enough nutrients for the starting of the seedling. But I wonder if it will be enough for the seedlings to grow strong/large enough that the roots actually show through the RW cubes, so I know I can transplant them to my organic soil.
If the roots do not protrude the RW cubes before I transplant them, I am worried that not enough nutrients will reach the root zone inside the RW cube once transplanted, as basically the only nutrients coming through would be from organic soil directly on top of the RW cube that "drips its nutrients down into the RW cube" when watering...

With cuttings I basically have the same worry only amplified because I believe that cuttings need more nutrients than seedlings. What with them being bigger already and having no seed that affords them any nutes...

I was hoping that something like a bottle of Rhizotonic will do the trick here.
But would obviously be glad if plain tap water would work ...
Or maybe some aloe vera juice mixed in or something.

Any experience and feedback welcome.

Stay frosty my friends
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Old 11-30-2018, 01:08 PM
Byorn's Avatar
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Posts: 532

hey Bro,

1) cant say for sure.

2) I havent had the best results placing a seed into rockwol plug without fertilizing them. It can be done, but i suggest when you see the slightest of the taproot coming trough, to transplant that moment. That would be after a day maybe 2. This worked out for me several times. If i remember right they did fine till day 3-4 then they start showing the first troubles.

I would go for a bio-mineral nutrient. Like GH flora nova grow. Thats just one bottle.

or kick out the rockwool plugs and start in dirt straight away.

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Old 11-30-2018, 01:21 PM
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Join Date: Feb 2018
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in my opinion you complicate your life using rockwool... personally I would recommend the Eazy Plug, the price is more or less the same as the rockwool, 100% organic, pH 5,5/6.0 and EC 1,0 stable and they self-regulate the air-water relationship...
very easy to use... fill a tray with a little water, put down the Eazy Plug and wait for a couple of minutes to absorb the water... you do not need to wring them out or adjust them their water content... they self-regulate, as long as the cells containing the Eazy Plugs have the hole on the free bottom...
vivere tota vita discendum est et, quod magis fortasse miraberis, tota vita discendum est mori.

Last edited by Efesto; 11-30-2018 at 07:03 PM.
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Old 11-30-2018, 09:51 PM
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Join Date: Sep 2018
Posts: 2

Brohammed Ali (floats like a butterfly, stings like a bee)

Hey Champ, You should look into using Coconut water for clones and seedlings. The coconut is one of the biggest seeds on earth and the water inside is dynamite to cover all aspects of your 2nd question.

Not sure how available this product is for you but its called, Harmless Harvest Coconut Water. Itís pink tinted unpasteurized straight organic coconut nectar. A bottle (16 oz or 257ml?) runs between 4-6 bucks U.S. Another option would be tapping real coconuts.

Something to consider, hope it helps. - Flash
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Old 12-01-2018, 12:14 AM
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Join Date: Oct 2018
Posts: 100

I always use a plain mild potting soil in a plastic cup (think kegger party red plastic cup) with 5-6 tiny holes punched into the bottom.
Fill cup half way, water it and let the excess run out the holes. Put the seed in about 1/8-1/4 inch under, cover cup with saran wrap secured with rubber band.
Put under an incandescent light to warm gently.
Keep eyes on it, as soon as seedling breaks soil remove saran wrap so it can breathe.

I don't recall ever losing a sprout this way.

The old paper towel in a zip lock is guaranteed to lose 10% or more.

Why chance losing seeds on something you're not sure of?
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Old 12-02-2018, 07:03 AM
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Posts: 53

I've been using grodan rockwool for years.. both seedlings and cuttings.

I germ using paper towel, & once taps are showing, I place them tail down into 1 inch cubes.

I soak my cubes in plain tap water ph'd to 5.6ish (20min or so) Never any nutes until I see a few clusters of roots coming out the bottom. I will then place them into 4inch cubes, which have been soaking in 1/4 strength nutes over night (Once roots are showing)

Be sure to shake out a good amount of water from each cube before using. Don't squeeze/crush them, just whip the water out of them so they aren't sopping wet

I like to take my tweezers, & clean up the top hole in the cube, to prevent the seed from getting unnecessary resistance when it cracks the surface.. (I also tear a small flat piece of rockwool, and place gently over the hole and leave it there until the seedling is close to or pushing it up)

I place under t5 floros. Never in a dome. I watch them and give them approx 30ml or so of straight ph'd tap water each day, or as they require to not dry out..

Of course this is what works for me and my setup.. That's just what my process has evolved to over time..

I have provided many friends with plants in 4x4 rockwool, which they place into soil for outdoor grows, with great results
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Old 12-02-2018, 02:04 PM
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Hey Bro,

You can use straight tap water. the plants will need food and PH adjusted (normal range) water for the subsequent feedings. Or just use PH 6-ish water from the beginning.

You do not need to transplant as soon as the roots show.
Cubes act like air pots. The roots get air pruned. Creating more roots..

Note: I use an old baking tin for my seedlings, it is getting rusty, hence the red on the cube.

Also of note, I once went to the store to buy 4" Rockwool cubes. The guy tried to talk me out of them. I had only used 1" cubes before and thought the bigger ones would be just as great.
He tried to convince me to buy the half height 4"x4"x2" cubes. I did not bite, they barely cost much less and were half the volume!
I ended up not having good luck with the 4"x4"x4" cubes. Not sure why exactly, over and under watered at the same time? IDK. I just know, I never bought them again.
I stick with the 1" cubes. They work perfect. Then into soil or Hydroton or whatever.

I see that HWM705 has luck with the 4x4 cubes and I know others do as well. I just know I wish I had listened to my guy.

I wish you had bought the 1" cubes Bro. Plants can remain in them for longer than you would think.

These pictures are from the same plant as the roots shown above. A mango haze seedling

If it were me. I would cut those cubes up into smaller ones and use them that way.

HWM705 does seem to use the same technique as me, more or less. except I drop seeds right into the cubes.

- Never use a dome.

- Cover the hole with a small piece of Rockwool, torn from the cube. I don't touch the seedling. The seed casing is removed by having to grow through the ripped off piece of Rockwool. I also don't open the hole any. just drop seed in and cover hole. (or squeeze shut with tweezers)

- Keep them hydrated with PH adjusted water (nutrients preferred)

- make sure the cubes aren't sopping wet

- light nutes after initial watering

Good Luck My Friend

Last edited by Seed Collector; 12-02-2018 at 03:01 PM. Reason: wording
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Old 12-02-2018, 02:40 PM
Seed Collector's Avatar
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If I were going to use something other than a 1" cube. It would be something smaller.
Quicker to air prune, Quicker to planting. (although untried theory)
I believe the 1" cubes are the biggest in this picture.

I don't know anyone who plants in 4" cubes. I only know of people that transfer to them and grow colas.

One other thing to note if you do use the cubes to air prune the roots.
Make sure you water the cube for the first two weeks after transplanting. Or water really well and bury deep in soil.

The cube can dry out a lot faster than it's surroundings when it is packed with roots and the plant can die before it has a chance to get its roots out of the cube.
This is where transplanting as soon as the roots show will have a clear advantage.
As long as you take that into account and keep the cube watered for two weeks after transplant, You should be very happy.
Soaking the cube before transplant and burying at least one inch below the soil seems to work well too. FYI (in case you are transplanting to soil)

Last edited by Seed Collector; 12-02-2018 at 02:55 PM.
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Old 12-02-2018, 04:05 PM
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As far as fertilizers go.,
I don't use anything special.

Just whatever old flowering fertilizer I might have laying around.
I personally used some generic hydro fertilizer. Flowering. Two part. 1/4 to 1/2 strength.

Roots and buds like the same thing. Phosphorus.
If I didn't have a flowering specific formula laying around i would use whatever I had on hand.
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Old 12-03-2018, 09:29 AM
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one of the main draws of the 4x4 rockwool cubes to me was that they have the outer layer of plastic around each cube that I can use to mark them.

Always struggled with marking my jiffy plugs or eazy plugs or root it plugs or anything other I used so far.

I had considered going straight into soil, as I have done before, in solo cups.
And I might still go that route in the long run.

But I did germinate in jiffy plugs instead of solo cups because I had better success with the jiffy plugs. My assumption was that they are more compact around the seedlings and thus help them better in rooting. While the soil in solo cups is a bit too loose for that.

For cloning, I have a ready DIYed aero cloner sitting there, waiting for me to try it out.
And I will.

If that works like a charm, as I suspect it will, then I would just go straight into solo cups or even straight into the 1 gal pots, since they will have an established rootball already.

But what will be my method for seeds? Can't sprout them in the aero cloner and had better results with jiffy plugs than with strait into solo cups with soil mix.

So I was looking at the rockwool 4x4s as a solution to all of these issues. And it was suggested so many times by people here and elsewhere.
AND it helps me with marking each cutting/seedling. Which has honestly been a nightmare in the past. I had to use 3 propagators instead of 1 or two because I could only ever use the outer edges of the propagator since I couldn't mark anything in the middle .... (I just taped some scotch tape around the bottom of the propagator and wrote on that but tearing it off again cleanly for the next round etc. was really annoying, too).

The question to me now remains:
If I try to clone and sprout seeds in the 4x4 cubes, do I just go with my tap water (which is HARD --> ~350 ppm) or do I add a nutrient base. To me it sounds like a nutrient base should be added.

Coconut water sounds nice and appeals to my organic head. But it is hard to get here in larger quantities. Basically it is only sold for consumption by humans, meaning it is sold like bottled water in small half liter packs and expensive as fu**.

I was thinking about getting a nice, large Aloe Vera plant and just squeezing out the juice and mix it with my tap water for the clones/seedlings start in the 4x4s before going to the rich soil mix.
Would that be an alternative to coconut water/bottled nutes?

Otherwise I will just get a single bottle something I suppose. Had my eye on tha Flora Nova line as well.
Can't get maxicrop here or I would use that I suppose.

The question was then which bottled nute I should take if I only ever want to use it for the absolute starting phase of seedlings and clones in the 4x4 cubes.
A 1 part solution like Flora Nova sounds good.

If I didn't have you guys, I would have probably just gone with Canna Rhizotonic. But I assume that, while stimulating root growth, it doesn't really afford the seedlings/clones with the nutes they need in that early stage, correct?

Once they are planted to soil, I also don't really need any other root stimulant, since I have excellent micorrhyza that do the job quite well, once they hit the organic soil.

I hate myself for always lumping various topics together but here we go:
Also currently run into the issue of wanting to transplant the veglings from 1 gal soil to 5 gal soil and not knowing which are female.
In the past, due to my excessive veg times of 2 months+, the plants were always so mature by that point that I could identify the females through their presex flowers with about 90% accuracy.

However, this time around, with all the topping, training and bondage, the plants seem less mature after almost 2 months veg and I can only make out the female pre-flowers on a hand full of them.

Now I am at the point I need to take cutting of all the veglings anyway and am considering to simply take 2 cuts per vegling.
Leave one in the veg chamber to root and throw the other clone under 12/12 and sex them.

Never done that before though...

So another question:
If I take a cutting, apply rooting gel and no tap water, nothing else, can I
throw that cutting under 12/12 directly, before it has rooted for sure, and will it basically root and start flowering simultaneously so I can use that method to sex them? (this would be another plus for the rockwool cubes as it would just cost me 15 cents per cube for this)?
Or do I have to let it root first under 18/6 before I let it flower to determine sex?

I am asking because I remember having forgotten some clones in a propagator on the window sill one time and they eventually all started throwing female flowers and I am not entirely sure there weren't some males among those cuts.

So I wonder if this stresses the cutting to the point where it just herms and will always throw female flowers ...

Any and all feedback welcome.

Last edited by Broseidon; 12-03-2018 at 09:31 AM.
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