thoughts on rockwool

[ronby]

I have several questions and thoughts about rockwool. But let me start by saying that I have only been growing for about 1 year. I began growing because I was tired of dealing with all the vagaries of scoring.

I have been using soilless hydroponics since the beginning because it seems to be the most efficient method of growing. It has been a very enjoyable learning experience and an unexpectedly fascinating hobby.

Up to this point, I have started my grows with seedlings planted in 1.5” rockwool cubes that were placed into a container of explanded clay pellets after roots began growing out the bottom of the rockwool. Because hydroponic containers are deep, I top-feed the plants until the roots got deep enough to be nourished by an ebb & flow table. For as long as I fed from the top, which was usually twice a day for seedling/early veg, algae grew on the top of the rockwool cubes. When I switched to ebb & flow, the algae would die (because nutrients didn’t reach them). When algae was growing, it never seemed like a threat to the plant, so it did not concern me. When the roots got mature enough, I increased feeding to 3 times a day.

FACT: Explanded clay pellets drain very swiftly. Rockwool cubes retain a lot of water.

As long as I was using only starter cubes, this was not a concern…

Now I am expanding… for my latest grow I’ve created separate veg & flower rooms so I could make clones. I am growing Mandal Seeds “Satori,” and Barneys Farm “G13/Haze.”

But for this grow, I decided to take the rockwool starter cubes and plug them directly into 4” rockwool cubes after germination, instead of expanded clay. This is where the difference begins.

After much searching on the subject, I have found little information on rockwool cube issues, beyond how to get them properly started… so I figured there was nothing else to know. Since it is claimed that one cannot overwater in rockwool, I kept the same twice-a-day feeding schedule as I had before. Mistake. I’ve also found that even though the 4” cubes are ridged on the bottom to allow water to drain away, the wicking properties of rockwool doesn’t allow that to happen… and my rockwool soon got very, very saturated. My plants began experiencing the symptoms of overwatering.

NOW: these 3-week old plants have begun growing out of the bottom of the 4” rockwool cubes, so I haved placed them on top of clay pellets set in hydroponic containers and raised them off the tray so water won’t pool at the bottom. I placed the 4”rockwool cubes on top (rather than in) the clay pellets, because I know that marijuana roots are long and this would give them extra depth. I think that the clay pellets beneath will help wick excess water away from the rockwool. I plan to continue top feeding until the roots get deep enough to be fed by the ebb & flow table.

But I think that for as long as most of the roots are being fed through the rockwool, I will water only once every other day (or even every third day).

It seems to me that if one is growing in rockwool, than the whole hydroponics feeding routine is different. If so, it’s odd that it’s so hard to find info on it.

I’m curious… what would you do differently?


http://www.icmag.com/ic/gallery/showphoto.php?photo=779782

 

[ronby]

the new container setup

 

[lysol]

I recently tried the handwatering rockwool thing, I found my runoff varied wildly in EC and PH, I found just placing the cube into a bubbler so moisture is constant and from the bottom works best, as soon as the roots poke thru you can plant it and put the water level below.

Yes you can overwater in rockwool, and personally I found better results when I treated it like soil, keep in mind nutrients CAN buffer up inside the cube if you dont water to complete run off. It helps to have some wicking action of the hydroton so you can water thorough and not over water, A cube sitting on a tray can be overwatered IMO, you can also overwater a cube in top feed in a medium IMO, in an ebb and flow it would be better because the moisture wicks to the top of the cube, maybe its getting the right amount of air that way

 

[Kindman69]

Cheers mate, there are some concerns that I have with what you are doing. I would say that you can do it the way you have it set up as long as you water from the bottom up i.e. flood and drain, and if you make sure that the flood level never reaches the rockwool.
Rockwool will get waterlogged in a hurry, do NOT believe people that tell you that you can not over water in rockwool, been there done that. The next problem with rockwool is that due to the reduced watering that is required you will build up nutes in the medium in a hurry and periodic flushing is required, meaning you have to be in top[ of your 'runoff' readings (ec, ph)
Back to your picture, the reason it will not work with top feeding is that the hydroton will require far more watering then the rockwool, which you can not due while you top feed.
You can tell that I hate f'n rockwool lol, I would go from the starter cube directly into hydroton and after a week or so do a 24/7 top-feed & recirculate. That way you can eliminate flushing during the grow, nothing will build up in the medium as long as it gets constant or near constant water flow. I use 100% perlite for the first time, not even a starter cube lol, so far they like it.

Here I type all of this before reading Lysol's comment lol, right on Lysol

Good luck ronby!

Kind

 

[ronby]

thank you for your input... glad to hear i'm not alone in this.

yes, i believe that with rockwool, it is better to treat it like soil when it comes to watering frequency.

i hear you about the difference in nutrient build-up levels between the rockwool and the expanded clay pellets (is that hydroton?). it complicates flushing.

I plan to switch to ebb & flow feeding when i believe that the roots get long enough to reach the flood level. then again, maybe the wicking action of the clay pellets will get nutrients to the roots even if they don't reach all the way down yet?

thanks!

 

[Wait...What?]

read my .sig for rockwool watering with drip lines.

water early and often when using hydroponic methods.

i frankly dont see any real difference between growing in hydroton/rockwool/perlite/lava rock/sawdust/coco [coco has quirks the others dont]

 

[kwamtime]

I use rockwool now in a ebb and flow tray. I start the cutting in 1.5 in cubes once rooted stick them in the 4 in and once those have rooted place them on top of the 6 in or new 8 in cubes, it works great for me. You do however want to be carfull when watering from the top because of algae. Also the nutrient retention in rockwool is high so you must keep a close eye on this and flush periodically. Other than that its gravy!!

 

[ronby]

kwamtime... really cool looking setup. i notice you keep paper on the bottom cubes. how deep and how often do you flood? (sounds like a sex question doesn't it?)

 

[RockyMountainHi]

I am about 10 days into flower in my first rockwool grow - I used 6-in Hugo blocks in a flood and drain system - I've varied feedings and so far seem to do best with one a day. I can go 2 days - but the trays get very light.

Growdan site says using flood and drain - the blocks need to be flooded 2/3 of the height - (4-in) otherwise salts build up. any higher and peeps get mold and stem rot issues. - Getting mold? - cover the blocks with plastic, that will stop the light and take care of the mold etc.

Rockwool drains differently with something underneath it - expanded clay or coco mat will alter the watering schedule - My blocks are on a plastic tray - multiple strains and differing harvest times - when I can run entire trays of the same clone - it will be Hugo blocks on top of a 1-in coco mat.

If you pre-rinse your blocks - leave them on a flat tray then later, tilt the tray, each time check the weight of the blocks - now stack a couple blocks on top of each other - it's like turning on a faucet - the extra water that drains. The bottom cube tends to hold more water. Rockwool does have a big advantage - it can be wet and the roots can still get oxygen.

I've pH treated most my blocks with 5.5 and then drain and dry - and I used a few blocks with no pre-treat, and they had more pH up swings. Back to pre-treating

I have a friend using 6-in blocks and floro's/400HPS, and I use floro, 400HM and 1000HPS - the blocks have no problem keeping up with the higher light output set-up.

Out of the 44 original starts - I didn't loose any till the males started showing up - I'm down to 26 girls now - a couple have issues - a little leaf necrosis - curled leaves - just not quite happy - but the other 3 in the tub are fine, so majority rules.

let me get ya a link to my shake down run,,
http://www.icmag.com/ic/showthread.php?t=122314


There are a couple posters that warned of issues you are having - stop by see what may help.

 

[Haps]

I do not like RW, it itches, nasty stuff, unhappy little girls when itchy.

 

[Wait...What?]

I do not like RW, it itches, nasty stuff, unhappy little girls when itchy.

ever step on hydroton in bare feet? for tiny round balls, they sure hurt. and the little bastards get EVEYWHERE

rockwool is the least messy of any medium, but i could probably make a mess even growing medialess...

 

[Tinytoon]

I myself am getting ready to quit using RW all together. Use Rapid Rooters to get things going then put directly into Hydrotron and let the flood and drain start!

 

[K Double O]

I have had bad experiences with rockwool. Not a big fan. Algae and mold are just some of the issues using rockwool.

Not only that... I feel like when using soil mixes, rockwool, rapid rooters, starter plugs, etc... Are an attempt at idiot proofing the whole "seedling" process....

I have a home built 40 site areo cloner which cost about $35.... It works like a charm... I have yet to not root a cutting..... From there its straight into my soil mix....

To each, his/her own. Just be careful with Rockwool.... They can be very trickyy...

Unless used in hydro.... I'm Pass on Rockwool altogether...

 

[ureapwhatusow]

rockwool is an amazing medium

i have used many rockwool and rockwool hybrid combos

for cloning i get excellent results every time, rapid rooters are good too but rockwool maintains moisture longer in arid conditions

I have used 6" rockwool cubes for veg and then transplanted to 12 wire baskets with hydrotron in ebb and flow much like you have shown, except I match top of flood with bottom of cube

I myself would flood a hydrotron rockwool combo and i woudl extend the depth of the flood zone hydrotron requires more watering than rockwool to maintain proper balance of water and air, you can hand flood the cubes top down with water to wash salts outta the cube but i never had an issue and ive done ebb and flow extensively this method

it helps keep a core of the root ball protected if you lose pumps (the whole reason i did it) and the amount of root space in the hydrotron is increased by the larger container


bottom line is that if hydro = bigger plant smaller root then huge hydro rootspace = huge fucking trees in any hydro medium

scrog or LST to get similar results as sog will lower density

these larger containers also give you more rootspace before the roots lock into a mat in case you need to take something in to out of the system

However if you want to handwater and you want giant plants use rockwool cubes on rockwool slabs

this is the rockwool equivalent of planting in a bed which lets plants share an increased rootspace

I think that rockwool 6" cubes or 6" slabs with 4" cubes are the best medium for vertical and if were in a position I would be experimenting with that design

IMO the big detriment to rockwool is disposal and that issue keeps me form using it as a sole medium

 

[Securityfirst]

Here is a pic of my vegg setup, obviously fed from the bottom.1000 watt MH and 600 HPS, I have algae because I use straight tap water. Over the years Ive noticed that rockwool like to be kept clean and have their space to breathe, although algae has not done any damage to my plants ever. When I transplant a clone in rw into the bigger RW I score the bottom with a razor to make room for the roots so as not to stuff it in there. I think that a better method is to put the rockwool into a 3 gallon mesh bottom hydro container filled with 80 coco and 20 perlite mix and either top drip or flood and drain.

Try that you might never go back. The way your plants are set up now doesnt allow for much air flow to the roots. You could also try smart pots with the 80/20 mix as well.

 

[ronby]

this is all good information, even if a bit contradictory... i am obviously commited to the rockwool/hydroton combination for this particular grow... next grow?

...and it's not so much a question of whether i like rockwool or not... it is that it must be used differently than other types of hydroponic feeding regimes, and there is little information about that to work from... and despite claims to the contrary, if not done properly, one CAN OVERWATER in rockwool.

 

[Jellyfish]

... and the expanded clay pellets (is that hydroton?)

YES!

 

[kwamtime]

I keep the plastic on because the roots dont like light. I flood the tray every other day about 1/4 high on the bottom cubes. Good luck !

 

[Hydrosun]

Also I use coco caps which fit over the RW cubes (stops light) and the coco cap is supposed to control rot and algae growth. I am introducing a res chiller when I swithc to flower this time. Algae loves warm H2O let's see how it likes it when my buckets are drinking from 64 degree formula!

Coco cap in action and stem the size of a 1U$


Peace,

 

[ronby]

you see... watering once every other day with rockwool cubes is really different than three times a day with hydroton. and yet, none of the books i've read and none of the how-to tutorials or growing guides address that... so it came as a surprise to me.