Cloning in Rockwool Cubes

I know I started a topic on cloning before, however I have more specific questions this time.

We have changed out cloning techniques. We were originally using EZ Cloners(aeroponics). The res contained a mild nutrient solution (EC: .7-.9, pH: 5.8-6.1). The clones were cut and usually ready to plant within our scheduled time of 17days.

Now we have switched to rockwool cubes in a flood tray system. The res is filled with a mild nutrient solution. (.9, 5.7) We have a water chiller and a UV filter, the soultion is aerated as well. I do a partial change of the res every week. Generally the water solution is at 68 degrees.

Bear with me, I am new to rockwool.
Upon taking cuttings, I soak the cubes for 30+mins in the solutions, pH’d to 5.5. I use a gel hormone dip.
I have taken cuttings and put them directly into the system to be irrigated once a day.
I have also taken cuttings and put them in a tray, domed, both on a heat mat (at varying temps, from 75-80 degrees) and off of a heat mat. After a week of being domed, vented slightly, I have put them in the system to be irrigated once a day.

The rooting time has increased by a week. It’s literally taking a month to see roots poke out the bottom of the cubes. Certain strains, the leaves turn yellow, and look poor over all.

I was hoping to shorten the rooting time but I have added a week to it and overall I wouldn’t say the clones have improved any.

Any tips/pointers would be greatly appreciated. Increased irrigation? Temps? Less frequent irrigation?

Thank you for you time!


Hi Anne,

Thank you for the question.

I would recommend soaking the cubes with 1.5 EC/ pH 5.5-6.5 from the start. Since you took the cutting off a plan that was receiving full nutrient and of the rockwool has none you want to supply the clone with some nutrients from the start. You do not have to soak for 30 minutes but just enough to fully saturate the blocks. Also depending on the dome and your environment I would vent the dome fully from the start. You are aiming for about 80% humidity. After you take the cuttings and place the dome I would wait about a week before watering again and transitioning the dome off over a day or two as your environment allows. Then you should wait a few days between the first few irrigations to allow the block to dry back some and the plant to develop roots.

Please let me know if you have any additional questions.

Best Regards,

Doug Jacobs
Grodan Technical Advisor


Thanks Doug! I’ve also been having some troubles getting roots to grow. It’s amazing how good the leaves can look in a dome though no roots have grown at all! I just ran in and added some mild nutrients to them as well.

I’m using a mix of mostly perlite with a bit of soil.



As far as temps go, what you would say is ideal? Should they be put on a heat mat? In the flood trays I’ve recorded temps between 64-70degrees.

I have a thermostat for my heat mat and I’ve left it at 75, I think the Grodan site states the heat mat should be 85. But with a dome, temps would get up past 95 inside the tray with crazy humidity, even with the dome vented.


Having taken a clone or two in my time, I think I might be able to share some insight. Firstly, I love rockwool for propagation for many reasons: mainly, it’s clean and easy to work with.

So, based on what I’m reading here, everything you are doing sounds spot on to me. Your temps and humidity levels are correct, your pH and EC ranges are where they are supposed to be. You’re changing the res out frequently. So what’s going on?

My suggestion is super simple and it should reduce your total workload as it will reduce time spent on maintenance as well as lower your water bill. Here it is: Try cutting down such frequent irrigation. I find that once the rockwool cubes are pre-soaked, their moisture level stays constant for about 5-7 days with the dome in place. Another simple suggestion is to lightly mist the inside of the dome occasionally rather than watering the cube or spraying the clones’ foliage. Spraying the dome will serve two purposes: it will maintain the RH level within the micro-environment and it will encourage the plants to focus energy on rhizosomal production (root growth).

I’ve found that these simple practices allow for me to focus energy on other aspects of the cultivation facility instead of constantly babysitting cuttings. I have about a 98% survival rate with an average rooting time of 10 days. Try it out. I believe this will half the time it’s taking your clones to root and get you to that high success rate! Hopefully this helps!

Happy Growing


I’ve never been satisfied with the time frames in comparing EZ cloners to rockwool. I’ve found the aeroponic EZ cloner setup to be 7-14 days vs 10-20 days in rockwool. Some of the suggestions to let the cube dry out more make sense. But I will still bet you will never root as quickly in rockwool as with the ez cloner.



Great advice on the misting. Since there are no roots the plant cannot get enough moisture from sitting in a moist media. In our greenhouses we mist every 20 min for the first few day then start backing down over then next few days. The plants need to remain Turgid (no wilting) or it will really slow things down.

Also check the rooting hormone, some formulations are too strong and will burn the end of the stems so they can’t callous nicely and roots cannot form


When I was working in the greenhouses at a botanical garden we misted clones at about this frequency as well, except we were using a mix of perlite/vermiculite.

How would a person know if their rooting hormone is “too strong?” I have seen stems rot from too much rooting hormone left on the stem, so I could totally understand this being a problem.

Good input, everyone! Thank you!


You are exactly right, it burns them, and you will see discoloration where the hormone is. Most people over apply rooting hormones. Almost all rooting hormones consist of varying concentrations of (Indole-butyric acid ). If using a powder like Hormodin, you should use the .1% powder, just barely touch the end of the stem then blow off any excess. It’s not uncommon to see growers pouring powdered hormone into a bowl and sticking the unrooted cutting (URC) into it up to an inch high and “nice and thick” coating. This is just asking for trouble and even if it doesn’t burn the URC it makes for uneven rooting.
I prefer the Hortus IBA WSS. We use a rate of .944 grams per gallon. What’s nice about this is you can stick your cuttings, get them layed down and watered in and then put this on as a heavy spray, make sure to get it on the soil. There is no re-enrty time on it and you don’t have to worry about your employees breathing in the power or getting it all over themselves.
It seems kinda pricey when you order it but .94 gm/gal is a low rate and it will last. But it can up to 5 days off your rooting time and that is worth alot.