Avoid compressing the rockwool cube after soaking in water in step 1. You want to keep the fibers loose to allow the roots to easily penetrate them.
Soak your cube in the 5.5 pH water 15 seconds. You dont need to soak the cubes too long, they quickly will wick up the moisture. Remove from the water, gently shake away excess. Now you’re ready to add your seed.
In hydroponic growing the plants’ roots get their nutrition directly from the watering solution. So you can use rockwool in hydroponics grows to start seeds, and you can move to larger sized rockwool cubes once rooted.
When to transplant rockwool seedlings
The most important considerations for caring for seedlings in rockwool is to go easy. Avoid harsh light. Use light nute mixes. And don’t let the rockwool cubes fully dry out.
Go very light, start with a 25% strength mix. Work your way up to 50%. You don’t want to overdo nutrients when germinating in rockwool, the new seedlings’ roots are very delicate.
Where should weed seed be placed in rockwool cube?
Using rockwool in hydroponics for the entire grow cycle isn’t a method used often by first time growers, as there isn’t as much wiggle room in having the cubes dry out vs. using something more forgiving like coco coir. But since the rockwool dries out easily and can also absorb a lot of water given the size, so you can grow some very strong root systems which in turn can generate large yields of cannabis per plant.
You can also germinate seeds the old-school way, putting them in a sunny window. Just make sure to avoid extended direct sunlight when the plants sprout to avoid killing them off, as the rockwool cubes can dry out very quickly in sunlight (especially the smaller 1″ x 1″ cubes).
The pH Meter I bought was new so even before I could start soaking my cubes I needed to calibrate it first.
Instead of tossing away the reduced pH water I saved some in a separate container. As you wait for your seeds to sprout you may need to re-water the rockwool cubes if they get dry. Re-using this water saves you from having to mix up another batch of reduced pH water.
Soak the Rockwool Cubes
From this Question & Answer post someone asked if you could use rockwool outside and answered:
There are many numerous methods germinating seeds. Popular methods include using paper towels, solo cups or just directly inserting seeds into soil.
Insert the Seeds and Store
Now that the cubes were properly prepared it was time to insert the marijuana seeds and store them in an ideal sprouting environment.