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It's 420 somewhere

Hydro with rockwool and Clay pebbles

Hi all,


I'm a complete noob to all this and need to get some decent advice before I get things going as the seeds have arrived!!


I have very little space to play with which meant I got a 75x75x200 (WxDxH) tent, 450w LED light, carbon filter/extraction fan, a 65x65 wilma with 4 x 11ltr pots.. I have a bunch of extras like oxygen pump, heater (as the tent is in a shed, a concrete shed but a shed all the same), oscillating fan etc.


This will be my first grow ever and the advice I get seems to change often, I've been reading this forum and everyone seems happy to help so here are my questions..


  • I was told to use 1" rockwool starter cubes, move them to 4" cubes once ready and then the 4" cubes into the 11ltr pot filled with clay pebbles.. Is this a good way to go as some people are telling me not to put rockwool in with clay pebbles?
  • If I do stick with this medium setup do I drip feed or flood as rockwool and clay seem to prefer the opposite method?
  • I appreciate there is no real set watering schedule but if i am going with rockwool held in clay pebbles can anyone give me a good starting point for the number / duration of feedings the plant should have? i can dial it in from there.


I will be on an 18 on 6 off light schedule (maybe 19:5 just to test it) and was told not to feed during the dark period.


I think i have the EC / PH / reservoir cleaning all down and i will pull back on the nutrient dosage to around 1/4 of recommended as I am growing autos and that seems to be common advice from everyone.


Any tips / advice you can offer would be really appreciated :)


Let me know if any of you need more info on my setup before offering up ideas.Thanks


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my advice would be-don't use rockwool.

its not a good medium for hydro, as it holds on to too much water, and affects the ph drastically.

I would use root it cubes instead. Just put the seed into this when it has cracked after 24 hrs in water.

Place this into the net pot, with hydroton - clay pebbles. Flush all the crap off the hydroton and sit the pebbles in 5.6ph water for at least 24 hours before starting or putting the pebbles into the system. check the ph before removing hydroton, you want it to be about 5.6/5.8

Use the blue drippers and put them on a drip.

I would use a aquarium heater, sized to the res capacity,  in the res, set to maintain 18 degrees. If you manage to maintain the shed temp at around 19/20 degrees, you wont need an aquarium heater.

start them at 0.4EC ph 5.6, and check the ph as it will rise up over a few days, when it gets to 6.4, re-set it back with ph down to 5.6 .

insulating the shed will help to maintain temps, and you will use less electric on heating. 

for feeds I would start with 15 minute feeds 3-4  times a day during veg.


good luck with them. A decent root stimulant will work wonders with autos.

Edited by badbillybob
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3 hours ago, It's 420 somewhere said:


Thanks Billybob, appreciate the feedback, I have already done the flush on the pebbles and they are presoaking atm. I might do away with the rockwool and switch in a 60/40 mix with coco instead.. so many choices but i guess i will learn what works for me when i try them.


I thought the same thing about an aquerium heater, i got a little 50w just in case it gets too cold 'Winter is coming' 

I got some Mycorrhizal Fungi for aiding in the root growth so i will see how this all comes together 

Edited by It's 420 somewhere
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the only downside to using coco is that the coco will inevitably end up in the res (clogged pumps, feed lines  etc) .

I would just use hydroton if I was gonna do a Wilma , but its up to you, and I wish you luck with it.

Edited by badbillybob
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23 minutes ago, It's 420 somewhere said:

60/40 mix with coco instead..


Everything that @badbillybob says.........no to the coco, stick with the pebbles alone. Definitely no fecking rockwool, evil nasty stuff!!


Different mediums hold different amounts of liquid, when you mix more than one it can make watering a problem.


People do soak pebbles but it isn't necessary on first use as they are ph neutral, just a rinse to get rid of the gunk, if you re-use them though, then they have to be treated.


I'm in dwc, also in the shed so temps can be a challenge, my res is set at 20c and never strays more than 1c either side.


This allows the room temp to be lower as the roots are toasty, not ideal but it works.


I recommend a fan controller which will help to keep temp and humidity in range, keeps the noise down too.


Good luck bud


stu  :oldtoker:

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Thanks lads.. 


I thought if i was going to only use pebbles alone i would need to either do a flood and drain system or i would have to leave the drippers on constantly as the pebbles don't retain moisture etc. and the drippers don't tend to get all of the pebbles wet, just the area they are aimed at which would stunt root growth??


I could add more drippers, the pump shouldn't have a problem with that, i only thought of doing a coco mix simply to help it hold some water if I was doing away with the rockwool.

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I wouldn't leave the drippers on constantly.

If you are concerned about them drying out then go with more frequent feeds, like say 15 minute feeds every 3 hours during lights on, That would be 6 feeds a day during veg (based on veg being 18 hour period) don't feed during the lights out period in veg.

2 drippers per pot would probably help, but if you did use 2 you could knock a couple of feeds off, or feed every 4 hours for 15 minutes.

the hydroton does retain quite a bit of moisture, especially below the surface.

You don't want the drippers right at the base of the seedling either, it could cause dampening off of the stem, place them at least 40 odd mm from the stem, to get the roots searching for moisture/feed

I wouldn't go more than that, feed wise, to be honest, and even at this it might show signs of overwatering (leaves wilting down or clawed ends).

there are a lot of differing opinions on how many feeds to do, but this is what I would go with.

Edited by badbillybob

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Thanks Billybob,


I got some root it cubes yesterday. I will germinate in them and then transplant strait to the hydroton pebbles, i will play around with the drippers or just do away with them and fit a watering ring as they give better coverage, i will dial in the feeds/watering times as i go and i will keep an eye out for nut burn / over watering etc.


Thanks again for the advice, I want to do a grow in every medium there is just to get some experience and see what i like to use etc. first up.. root it and pebbles... I will post an update on my little northern light autos at some point even if its a fail but i will keep my hopes up :) 

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It might be worth running the light 24 hours,It may work out cheaper on the electric by not using a fan heater or such,to keep the temps up during lights off period.

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I had the same thought Ursus1000 i figured i would do this crop and monitor how often the heater comes on (its not a fan its an eco heating tube which should use a lot less power) and how much elec it uses, if its coming on a lot during the night then i might switch to 24hrs lighting, I am not massively concerned on cost to run it all just more on what works for the autos and keeps their stress down 

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