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germinating cannabis seeds in rockwool

Rockwool is a man-made substance and it doesn’t break down, so it’s not the best for the environment. Avoid breaking up the cubes and breathing in the small fibers, they’ll damage your lungs.

Marijuana seeds grown in rockwool cubes usually germinate within a few days. If they still haven’t germinated after a week with proper moisture maintained in the cubes then your seed might be a dud. Once your seed germinates you’ll see two small leaver poke up out of the whole. These two leaves, called cotyledon leavers, are quickly followed by additional leaves that have the classic shape associated with cannabis plants. As the seedling grows taller the roots will continue to grow well. Eventually you’ll see white roots start to poke out of the sides.
Check moisture levels daily. Lift the cubes to monitor water levels. Seedlings grow best in light moisture since they’ll grow roots to seek out more water. But if the rockwool cubes dry out fully you risk killing the seedlings. The most important tip for beginners is to check them daily. It’s better to have a wet cube then a dry one.

Since rockwool cubes naturally have a very high pH, you need to offset this by lowering the pH of your watering solution. This is the most critical part of growing pot seeds in rockwool.

  1. Soak rockwool cube in one pint of water that is pH’d down to 5.5. No extensive soaking is required, but make sure water gets fully absorbed. Include rooting stimulant (such as 2 ml per pint of water of Canna Rhizotonic) to encourage root growth once the seed germinates.
  2. Remove from water and shake gently to release excess water.
  3. Add marijuana seed to the hole in the rockwool and push to the bottom gently with a toothpick.
  4. Place under a gentle grow light in a humidity dome to create a warm, moist environment.
  5. You seed should begin to germinate in the rockwool within a few days.

Starting marijuana seeds in rockwool cubes is an easy and effective way to encourage rooting. Rockwool is a reliable growing medium for pot seeds, and it’s suitable for transplanting to all types of growing including soil, hydroponics, and coco coir.
The marijuana seed needs to sit in the bottom of the hole in your rockwool cube. Drop seed in hold and very gently nudge it down with a toothpick or wooden skewer. Be gentle!
We like to use a large CFL lighting fixture designed for growing seeds and clones, placed an inch or two above the top of the dome. T5 fluorescent tube lights which are great for covering a tray of rockwool clones. You can also use LEDs, very low wattage HID lighting set far above the cubes, or even a sunny window. Avoid high-powered HID lighting such as 600-1000W Metal Halide or High Pressure Sodium lights, they are far too intense for young seedlings.

If you notice white fuzz forming where the seedling stem exits the rockwool cube then take action immediately!

It's easy to learn how to grow marijuana seeds in rockwool cubes in a few simple steps. Rockwool is a reliable growing medium for propagating weed seeds, and it's suitable for all types of growing including hyrdroponics and coco coir. Here's how you do it.