Soaking GRODAN to proper Ph for growing

Question 11: Soaking GRODAN to proper Ph for growing

Hello. I use propagation cubes and 3x3" blocks. I soak them overnight in pH 5.0 water to achieve a pH 6.0 for growing. My friend soaks in pH 3.5 water because she says the natural pH of GRODAN is around 8. What is the correct method? My water reads at 6.0 after the 24 soak. Why couldn't we just put the dry cubes on the table and set it to cycle every 30 minutes overnight. If we did this with a pH solution of about 4.5, it should give us a proper pH of 6.0, correct? Please advise. Thank you.

ANSWER:
GRODAN stone wool is pH Neutral! It is a common misunderstanding that GRODAN is alkaline and that one has to continuously adjust the pH, when in fact stone wool is pH neutral.

The confusion stems from the fact that GRODAN has some residual lime from production. Follow this simple procedure to remove this un-buffered lime. Begin by saturating the stone wool in pH 5.5 water ½ hour before use. There will be a rise in pH of about 1.0 from the residual lime dissolving. The final step involves flushing the "dissolved Lime" from the stone wool with your nutrient solution just prior to planting or sowing. From this point onwards, the pH neutral GRODAN stone wool will not contribute to any changes in the pH of the solution.

Note: Ensuring pH values remain between values 5.5 – 6.5 is essential for optimum plant development and optimum substrate integrity. If you condition GRODAN products with a solution pH lower than 5.0, you risk damaging the stone wool, so take steps to ensure values do not go below pH 5.0

Why does pH change ?
When the plant grows the pH goes up because of the root activity involved in nutrient uptake of the plant. If the pH is not going up, your plant is not actively growing!
When the plant gets ready to set flowers or fruit, the pH will briefly drop. So when you notice this drop, the plant is signaling that it is time to change to your bloom-solution.

So in answer to your questions; You should always stay above pH 5.0 (better to use pH 5.5), because GRODAN begins to dissolve below pH 5. You can soak the cubes on your table. You don't need to cycle, as long as the cubes are soaked initially. However, you do need to add the final step of watering from the top in order to flush out the lime residue. You should also get rid of the drained water, as it contains the lime residue.

Please download the leaflet “Watering and pH” or pick it up at your local hydroponic store for more information.