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Preparing & Sanitizing your Rockwool (Part 1 of 6)

Part 1 of 6: How to sanitize rockwool sheets and soak them to a pH of 6.0

Follow the instructions in this article to sanitize and soak your rockwool at the start of every grow cycle, before a single seed is placed. Rockwool leaves the bag at a natural pH of about 8.0, and the target for germination is 6.0, so every sheet gets the same treatment. Follow the steps in Keeping your Flex Acre Clean before you begin.

Gather Tools:

  • Rockwool Sheets
  • Perforated Mesh Tray
  • Non-Draining Planting Tray
  • Sanitizer Spray
  • Cold RO Water

Sanitizing your Rockwool Sheets

  • Lay your rockwool sheets flat into a perforated mesh tray.
  • Spray the sheets generously with sanitizer spray to prevent contamination.

Step video coming soon.

Sanitizing and soaking are two different jobs and they run in a fixed order. The spray sterilizes the growing medium. The soak, in the next section, sets the pH. The mesh tray is the one container your sheets stay in from here until they reach your seeding area, so load it once and leave the sheets in place.

Use only the rockwool supplied by Fork Farms, as rockwool alternatives void your warranty.

Soaking your Rockwool to a pH of 6.0

  • Soak the sheets in cold RO water for at least 15 minutes.

Step video coming soon.

The soak is doing two things at once. It lowers the natural rockwool pH from about 8.0 to the target of 6.0, and it saturates the medium with moisture so your seeds sit in a wet cube from the day they are sown. Pull the sheets early and you keep both problems, a pH above target and a dry core. A finished sheet is heavy with water when you lift it out of the tray.

Draining & Moving your Trays

  • Lift the mesh tray clear of the water.
  • Drain the excess water into a sink.
  • Set the mesh tray inside a non-draining planting tray to catch drips on the way to your seeding area.
  • Carry both trays together to the seeding area.

Step video coming soon.

The non-draining tray is what keeps water off your floor between the sink and your seeding table. Your sheets are saturated at this point and keep releasing water as you move them, so give them the sink first rather than the walk. Keep the two trays stacked together, as the mesh tray drains into the non-draining tray again during seeding.

Your rockwool is now sanitized, saturated and sitting at a pH of 6.0—well done! Continue to Seeding & Labeling your Trays (Part 2 of 6) for next steps.