How do I clone using rockwool?

The Fine Art of Cloning, by N.P.Kaye

Old school hydro growers still use small rockwool cubes for cuttings. They’re about 1.5 inches square, wrapped in plastic, and have a HOLE for the clone to go in. (Note: Rather than the individually wrapped cubes, Grodan manufactures a sheet of 50 cubes which fit perfectly in a standard tray/propagation dome.) You should remove the plastic wrap.

I usually poke a 1/8 inch diameter pointed stick in the hole to deepen it the original hole to a point 1/4 inch from the bottom of the cube (don’t go through the cube). That allows for approximately 1 inch of stem to be in the cube.

Pre-soak the rockwool:

Treat the rockwool by soaking overnite in a 5.2 pH 1/2 strength nutrient solution (If you’re using GH nutrients, that would be 2.5ml of each component per gallon of water.)

Then, before squeezing out any excess solution, rehydrate with a 6.5pH solution of the same strength. In other words, mix a gallon of 6.5pH solution, then use some of it to adjust to 5.2pH for the soak. Use up the remaining 6.5 pH solution until the clones root.

I use Hydrofarm liquid cutting concentrate (HF cutting conc.), widely available Rootone F works as well.

Prepare the clone:

When taking a cutting, always plan on having at least one node inside the hole, and 4 to 6 nodes above. My cuttings are about 2.5 to 3.5 inches tall plus approx another 1 inch below the surface. The stem width of my cuttings (at the cut) average 3/32 to 1/8+ inch.

1. Trim off the leaf/shoot that goes in the cube with a razor blade before taking the cutting (see above)

2. Make the diagonal cut on the stem (from the mom) about 1/4 inch below a node. Use a new razor blade with a small piece of wood behind the stem to serve as an anvil for making a clean cut.

3. IMMEDIATELY dip the bottom one inch of the cutting in the rooting liquid for about 15 to 30 seconds, tweaking it to dislodge any air bubbles that may be present.

4. Then gently push it into the hole (I usually use large tweezers to poke into the rockwool about 1/2 inch from each side of the cutting then squeeze the rockwool to hug the stem).

The first night the cuttings will droop, the second day they will start to lift their heads.

I’ve taken clones rooted in rockwool and transplanted them directly into a pot with soil with no problems at all.. that’s the joy of rockwool, virtually no transplant shock from disturbed roots. As long as roots can be seen coming from the rockwool cube it can be transplanted.

How do you recommend supplying nutrients to the rooting stem?
Nutrition is not as much of a concern as moisture is.

Leave the cube in a humidity dome at around 80 to 85 degrees F, with about 30-40 Watts/sq ft of fluorescent lighting on for 24 hours a day.

The cube should NOT sit in water. As long as humidity is high, you can spray with the 6.5 pH solution twice a day for the first 2 days, then once a day until it roots. But the humidity must be high; you should see condensation inside on the tray walls and maybe the leaves. I also spray the walls of the tray to keep it humid. Spray only the leaves not the cubes.

Check for roots around the eighth day by opening a cube in half very carefully. White roots should be exiting the node.

Keep in mind that the longer you have humid conditions the more likely it is to get mold or fungus; rooting quickly is one way to avoid lengthy humid conditions.

Once rooted:

When you first see the cutting is rooting through the cube bottom, you can stop spraying and start watering the cube, let the solution drain from the cube.

This is a critical time:, when you see roots, water the cube and open the tent a little to allow humidity to escape AND CHECK EVERY 20 MINUTES for ANY SIGN of wilting. If after the 1st hour with no wilting open the tent a little more, and check every hour. After 4 to 6 hours with no wilting, you’re ready to rock n roll. If any clones START to wilt replace the tent, spray leaves, and try again the next day.

If you have some rooted, some not, go for the humidity for a couple more days.

Using General Hydroponic’s ‘Flora’ nutrients and rockwool, and Hydro Farm cutting concentrate, I root in 8 days with great looking clones. So there IS a difference in nutrients, medium, and rooting compounds. BTW use a fresh mix of nutrients, and keep the bottle sealed. pH can shift radically, but usually wont do so for the first 10 days if the bottle’s kept sealed, out of light, and at room temperature. And don’t forget HUMIDITY, HUMIDITY, HUMIDITY. But don’t overdo it for too long or you risk mold and damping off.