I just thought I'd bump this post as a compliment. lazrbrn makes some great critical points about watering rockwool.
1. soak it, rinse it, be paranoid - I could add, some tap water is already closer to 8 pH(limestone aquifers) and it doesn't really help with dropping the pH. It would be better to soak it in a 5.2 solution overnight then rinse with a 5.5, tamp and load the cuttings. The pH of the rock wool will still rise because of the inherent nature of the mineral. and the final pH will most likely be 6.5 to 7. We tested this thoroughly at my university lab with unloaded soaked cubes and a very narrow pH probe.
2. don't water rock wool like a plant. - I could add, after soaking and rinsing the rockwool, tamp the base down five-times on a clean paper towel laid on a clean surface and get as much residual water out of the wool as possible. Think of it this way, we water to feed the leaves and buds, we water less to stimulate the roots to grow. That is why watering your plant every three days is better than watering your plant twice a day. If you're always feeding your plant there is no need for extensive root development. A humid and airy interior is what you want to create for quick rooting, it's the humidity, the whoremones and the oxygen all cycling inside the rock wool that drive root production.
3. Humidity dome is a must. Many people propagate without a dome and do fine. However, I want my clones done in a week, not three weeks. And I run a small confined operation with an underdeveloped mother who only affords about 10 cuttings and I need all ten to make it through cloning and into my pots. Furthermore, I need to get the grow done in short order in order to avoid the monsoon season, which rots my outdoor crop. So 95-100% humidity for the first 3 days and taper it down 10% each day after. I also trim my leaves to about half length. The rockwool will show some signs of light drying, but don't be deceived, it's still hella wet after many days. I only water the pan on day 5 and 7, the day 5 watering is necessary for me because I've got roots forming at this time and they deserve some reward for their efforts. I water the pan by running a solution across the bottom of the pan from one corner to the opposite corner and out a small drain hole. This actually waters and flushes any possible residues of microbes from the base of the pan. My watering solution is R.O. water (aired out to remove the ozone here or chlorine there) with 1 drop per gallon of superthrive and a cap-full of peroxide and a cap-full of isopropanol.
4. I add warmth. Just enough to get the cubes about 10 degrees above ambient (or about 75-80F) This causes a gradient and a reflux inside the rock wool which is subtly cycling trace nutrients and new oxygen across the new roots. By design the roots seek out the warmth, running from the frost.
5. My lighting is super low. I run a 100w CFL about 12 inches away from the top of the clone dome. We want to balance photosynthesis with transpiration. Photosynthesis is not very essential. A 4" cutting has a butt-load of sugar in the phloem juices and the cortical cells of the stalk. In reality you only need enough photosynthesis to feed the leaves. Keep in mind the stalk and the leaves are both photosynthesizing. Also keep in mind that the growth of a decent root ball is not demanding on the stored nutrients of a 4" cutting. Roots are a very simple tissue and exist primarily to transport water and nothing else, thus requiring less nutrients to grow. And very low lighting keep the interior of the rock wool darker also.
Everything else I do is similar to what you've read in many other threads. I take my cuttings cleanly only after two flushes(3 days apart) of my mother soil. I soak the cuttings in a very dillute superthrive (1drop per gallon) for about 1 hour, I re-cut, dip in olivia's or clonex, pre-punch my cubes, post pinch the tops. Mist my plants and dome with water to generate humidity.
The last thing I do that really matters is I don't touch the kit for the first 5 days. Not even a bump. If I have to mist I'm very careful to avoid causing plant movement. The root-tip meristem is very very fragile and any movement can add days onto the time it takes the roots to fully lengthen.
I follow this watering method from experience. I've screwed up a lot of cuttings in my early days using many different methods including aero and bubblers. I used to yield about 50% in those days, but can get 100 percent now. I clone about 30 cuttings a year and haven't lost a cutting since 2008. I've been cloning MJ since 1998.
Using this method I can usually get 5 of 10 clones ready by day 7 and the last five ready by day 10. I save a weeks time, sometimes two weeks time compared to others results. Two weeks of grow time matters a lot to me when I have to get a whole batch sprung between January and June living in the monsoon belt, otherwise the rain rots my colas.
Oh yeah PPM is low with R.O. water, maybe 200ppm max after you add the superthrive. But I think root growth relies on nutrients very little within the first 1.2 weeks. the superthrive does the job. Don't be concerned about adding additional nutes, I'm pretty sure it may hinder instead of help.
The cutting seems to be hardened by day 7. When I transplant to soil, and water generously without nutes the first time, I never see signs of stress from my cuttings.
Happy Planting!
... they are living.. but.. men.. WAAAAAAAY to slow..
i have been doing it wrong the whole time thank you