Rockwool nightmares. Help a noob?

[peppy]

So I've been growing cannabis successfully in soil for nearly a year. I made the decision to "level up" to hydroponics, specifically DWC, and got my feet wet by trying to grow bok choy, spinach, and various leafy greens in rockwool. So far it has all been going well.

My technique with leafy greens: I get a small tupperware style box, sterilize it, and put soaked rockwool cubes in the tupperware. After seeds sprout, I add a very small amount of water (1/8" - 1/4" or 3mm - 6mm deep) to the box and replenish it as the water is either absorbed or evaporates off. This method has been working very well with my leafy greens -- they're all just about big enough to transfer to an aeroponic tower after a few weeks of growing in my grow box. Healthy, consistent growth with very low failure rate.

I've tried sprouting several cannabis plants in rockwool. I keep my seeds vacuum sealed in the back of my fridge so I think they're still good. But I am experiencing a very low success rate. All of the seeds managed to pop their taproot out, but further growth did not happen. I am assuming the plants are drowning.

At least for sprouting my seeds, what is a good watering policy in regards to rockwool? Should I wait until the bottom of the rockwool cube feels dry and then drip a little water on top of the cube, like, teaspoon of water? feels bad wasting seeds

Also, from what I understand, in dwc you keep the rockwool above the nutrient solution and let the roots of the plant reach down to the water. Is it important to keep the rockwool moist or is it okay for it to dry out once the plant is able to drink water from the bucket?

 

[peppy]

Been a few days so bump for interest :(

 

[TheIslandIsGreen]

Been a few days so bump for interest :(

I would assume starting seeds in rockwool would be very similar to rooting cuttings. I soak my cube in very weak fertilized water. Then when full saturated I pick them up and give a shake to unload some of the moisture and then put my cuttings in the cubes and the cubes in a sealed plastic tub. Stick tub under a weak light and in 2 weeks I have nearly 100% rooted cuttings.

I should note the cubes are raised on a screen so they don't sit in water that condensates when the lights are off. I give them a spray with a hand pump sprayer if the start to feel too light (in water weight). You don't want them soaked, but you don't want them too dry either.

I figure seeds would like a similar situation.

 

[Gonnnn]

I would assume starting seeds in rockwool would be very similar to rooting cuttings. I soak my cube in very weak fertilized water. Then when full saturated I pick them up and give a shake to unload some of the moisture and then put my cuttings in the cubes and the cubes in a sealed plastic tub. Stick tub under a weak light and in 2 weeks I have nearly 100% rooted cuttings.

I should note the cubes are raised on a screen so they don't sit in water that condensates when the lights are off. I give them a spray with a hand pump sprayer if the start to feel too light (in water weight). You don't want them soaked, but you don't want them too dry either.

I figure seeds would like a similar situation.

That makes sense. Seeds and cuttings both like a warm, humid environment with good moisture balance. I’ve had good luck using a similar approach with some affordable genetics from The Seed Pharm and keep the cubes moist but not soaked, and they usually get off to a strong start.

 

[Ninjadogma]

Been a few days so bump for interest :(

Im gonna suggest something a little gross but it's a training exercise to help get you acquainted with what an appropriate amount of moisture in a rockwool cube is.

Take a fresh rockwool cube and submerge it in water. Take it out and give it a firm shake to purge excess water. Then put your mouth up to the rockwool cube and suck on it. If water enters your mouth, it's too wet. Give it another shake and try again. Once you get it in the right moisture level where the cube is fully moist but breathing, remember the weight of the cube and the coolness to the touch, and when you remoisten the cube, that's how you want to make it. A spray bottle works great and with a little practice you'll dial in how many spritzes you need to rewet. You got this!