how long to soak rockwool cubes
- Thread starter boatrowe
- Start date
nongreenthumb
Well-Known Member
Half hour in ph 5.5
potroast
Uses the Rollitup profile
Well, you are both right! 
Grodan originally said to soak for 24 hours, but has recently changed their directions to 30 minutes. So it's not the amount of time that is important, it's the pH. Rockwool is spun rock, and some of the rock is limestone. There may be residual lime in the rockwool, and lime, as we all know from our reading, raises pH. So the wetting of the rockwool is done with a low pH soup, to fix the lime.
Lower your soak solution to the low 5's, using pH Down, or a Bloom nutrient.
After your soak, rewet with a low-strength nute soup, pH 5.8, and plant away.
HTH
Grodan originally said to soak for 24 hours, but has recently changed their directions to 30 minutes. So it's not the amount of time that is important, it's the pH. Rockwool is spun rock, and some of the rock is limestone. There may be residual lime in the rockwool, and lime, as we all know from our reading, raises pH. So the wetting of the rockwool is done with a low pH soup, to fix the lime.
Lower your soak solution to the low 5's, using pH Down, or a Bloom nutrient.
After your soak, rewet with a low-strength nute soup, pH 5.8, and plant away.
HTH
Serotonin
Well-Known Member
Yea, I just germed 6 six snow whites in Grodan starter plugs... the 1" cubes. I got the 1/4 nutrient water's pH to about 5.6 and every seed popped in like 4-5 days. Also, I use a nursery tray and have one of the clear humidity domes over it. Just slap all of that on top of a heating pad set to low and spray a tad of water on the bottom of the tray.
So far, I've had 90% germination rate doing this. I never used too and it is probably because of the pH imo.
So far, I've had 90% germination rate doing this. I never used too and it is probably because of the pH imo.