how to use lime to counter mid-late stage pH drop in promix

[RubeGoldberg]

For the longest time, i've been an advocate of ample runoff of promix, but im starting to realize that the initial dolomite amendment might be wearing off on me as well.


At the moment my plants (week 6.5 of 9.5 week bloom) are getting around 5.3 pH runoff, in spite of ample runoff happening on a regular basis.

part of this problem is due to the fact that I feed heavy, but I'm starting to think the medium is working against me as well.


That being said.... For a top dressing, to counter the pH drop.
What type of dolomite should I be using?

I used about 2tsp of Dolopril per gallon of medium and watered it through, but runoff is still low. (I realize it takes a bit to activate)

Can I use Rapid Lime?


Also what is the best form of lime if I want to amend the promix during transplant?

 

[FunkBomb]

The best form of dolomite lime to use is the powder. It keeps the pH where it needs to be, but the only issue is that plants eat it quickly. I add it to every soil/soiless mix I make and it works wonderfully. I go with 1 cup per 1 cubic foot of media.

I run into issues sometimes when the plants eat through it too quickly. When I use 3-5 gallon containers I'll top dress with 2-3 teaspoons and then top scratch it in. Water heavily and it will make its way into the rootzone in no time.

This is what I use:

https://www.amazon.com/Dolomite-Mag...pons&keywords=greenway+biotech+dolomite&psc=1

-Funk

 

[Easy7]

What are you feeding the grow?

Oyster shells in the mix are more stable for buffering than lime. A pinch of agri lime in the solution will raise it. A pinch too cause that stuff is hazardous how basic it is. Seriously, a small truck load treats acres and acres.

 

[purplepassion]

Run a tea to supplement and create a partially living soil.

 

[PaulieWaulie]

What I have noticed is that my promix PH is staying very consistent. I have been re using it for a year so am on my 4th run with it now. It was 6-6.2 in the beginning and now is 6.1-6.4, I have never added dolomite lime and usually get 20% of water going in coming out for run off. Using 3G pots, and feeding PBP for the most part at a total of 600 PM ever watering, lately I have stopped PH ing the nutrients as the media ph is always so consistent no matter what. So far so good.

I am thinking my water is fairly alkaline at 220 PPM of mostly calcium carbonate (180ppm), so every watering there is a bit of buffering occurring.

 

[troutman]

If your worried about using too much pH up or down.

Test the pH of your nutrient water solution prior using it and you won't overshoot your end pH goal.

Eventually you'll get a feel of how much base or acid to use.

 

[Douglas.Curtis]

Overfeeding is probably the number one reason for low pH in the root zone. It's due to root rot.

 

[G.O. Joe]

I attributed it to the chunks of limestone in promix dissolving over time, but the peat staying acid for longer. So, I'd add extra crushed limestone or dolomite from the start. A cup of it per cubic foot.

 

[bsgospel]

I might be remembering it wrong but won't carbonates in acidic soil cause greater fluctuations in ph? Carbonates have better stability in alkaline soils, which is why gypsum is a better option/sul-po-mag in combination? Or do I have it backwards?

 

[G.O. Joe]

What is gypsum going to do for pH though. I think you mean the difference between dolomite and plain limestone of the same size. What they use is a mix of the two in pebble size. It's not quick to do anything, so promix be wetted for a week before transplanting to bring the pH up. The finer forms dissolve faster then are gone and this is the avoidable undesirable pH swinging. I have recommended the dolomite every time this has come up over the years, using the amount suggested by GH for a long time with their nutes. The dolomite in addition to having Mg takes longer to dissolve, so it's still around at the end after growing for months without transplanting.