Indoor Quick ProMix/peat question...

[Merlin]

I just finished a ProMix grow (peat based medium) and had problems with extremely acidic ph of my run off. I've found that I should have pre-wet the medium to activate the lime/ph-buffers in the mix that stabilize the ph.

My quick question is how long approximately in advanced will I need to put my ProMix in pots and get it thoroughly wet before it should be stable enough to plant my next round of AF seeds in?... Thanks!

 

[The Squid]

Hmmm. Generally we have an issue with Promix having too alkaline of a Ph as it dries out. I always pre water pots and find that it takes maybe a week for the lime to stabalize towards 7, and it stays lower when wet so that's why if you let Promix dry out too much, you may have to deal with lockout from high Ph.

By the time the planted beans grows up a bit, the lime will be working. Dolomite takes about 7-10 days.

 

[Scott817]

I have not heard of doing that before. I guess you can just try it a few weeks ahead and check the run off and see. When I used ProMix BX I added hydrated lime to it to bring it down. Since then I have switched to Sunshine Mix#4 that seems to be pretty neutral as far as ph goes. I also use Humbolt soiless that is about the same as Sunshine.

 

[Merlin]

Thanks guys. I guess I'll just add a bit more lime and start the pots a week before I start the seeds.

Perhaps I got a bad bag of ProMix... It seems there's not many people having this problem, but I found a few who mentioned the need to 'activate' the lime by getting the medium wet in advance of planting. I just couldn't find any one who ever mentioned how far in advance. Maybe I'll just go buy another bag from somewhere else to see if its a bad bag first.

 

[The Squid]

I have not heard of doing that before. I guess you can just try it a few weeks ahead and check the run off and see. When I used ProMix BX I added hydrated lime to it to bring it down. Since then I have switched to Sunshine Mix#4 that seems to be pretty neutral as far as ph goes. I also use Humbolt soiless that is about the same as Sunshine.

Lime to bring it down? You mean up?

 

[Muddy]

I've not heard of anyone having low pH issues with Pro Mix either. Usually it's a bit too high as it's pretty consistently right around 7 right out of the bag. Unless you amending it with some composted manure, guano, castings, etc., no additional lime is really needed. I only pre water my starter pots the day before I plant the seeds. When I transplant to the final pots, I don't water till after they are transplanted. There are a variety of Pro Mix products available, including a new retail line, which are a bit different from the traditional HP and BX most of us are using. Which one did you use?

 

[Merlin]

I'm using promix HP. Although the only local place that had it was lowes, who stores it outside, in case that may have played some roll in this.

But out of the bag, watering with tap water which is high PH (~8), the run off has a PH of 4. With my last grow, I couldn't get the PH of my feeding water high enough to bring the PH much higher then 5.5, so I had all kinds of stress. That's why I amended this next batch (from the same bale) with some powdered dolomite lime (1tbsp per gallon). I've got my fingers crossed... I'll water again tomorrow and measure the run-off and post the results.

 

[Muddy]

That really surprises me. I don't measure run off as I have a good soil probe. I check every bale or bag I use and they are always either 6.9 or 7. I'm curious now. This afternoon I'll do a run off test on mine and see what I get.