Dolomite lime and PH Runoff questions

OK after doing a thorough reading on here (and getting thoroughly confused ) I have two main questions RE: Dolomite Lime and PH Runoff.


I just transplanted my three girls in 12'' diameter pots (if my math is right equaling about .25 cubic feet) NOW I added 2 TBS of Dolomite per container figuring on the known practice of adding about 1 cup per 2 square feet. My question is do you think this is enough (literally seemed to be a "drop in the bucket") or should I add more..better yet will adding more be harmful.

For the trickier question..PH Runoff..some of you think this number doesn't matter others say it does. I personally have always had a PH runoff of (roughly) 6.0 (Had a nasty MG problem as well hence the dolomite to raise the PH..I think) But yesterday after transplanting my PH was only at 3.8. This was the first time I just went "au natural" as far as water is concerned (tap water left out over a day, dish soap (a few drops to act as a wetting agent) no PH up/down of water was at 6.5.

My question I suppose would be since my plants, other than some leaves being hit with MG issues (which were in turn caused by PH issues) were nice and big and green should I continue to do what I've been doing as far as Upping/Downing the pH BEFORE I add the water or should I let it be at 6.5 and just ignore the low runoff reading.


Thanks to anyone that understands this and can answer.

Just my opinion and some advice i was given. I wouldn't pay attention to the run off Ph .... as long as you have the lime in there and you keep watering with Ph'd water you should be ok. I had the same problem in a few past grows where i'd water with 7.0 water and the runoff would be at 5 or less ..... I continued with no problems ...THIS ISN'T FACT THOUGH. I'd suggest PM someone with a bit more experience

Thanks for the quick response ataxia..as far as PMing someone still somewhat of a "new guy" so not sure who I can PM...any ideas on who's real good with soil around here?

Run-off certainly isn't the ONLY way to determine the pH of your soil, but I think it can provide the grower with a rough idea whether it seems okay or alert them that they should do an actual soil test. The horticultural pH test drops are used primarily for checking the pH of irrigation water or fertigation solutions (after fertilizer has been added). There are inexpensive pH testing kits which are intended to be used with soil specifically, and these are more accurate. The soil kits come with capsules; you put soil in the provided sampling container, empty the powder from the capsule in with it and then fill with water, shake and wait for the result.

It is best to mix the dolomite lime into your soil before you plant into it. You can do it afterward as you did, and those amounts are fine just be sure you water it in thoroughly. You could also go ahead and mix a tablespoon or two of dolomite into a gallon of water and give it to the plants like that- keeping it all agitated while going from plant to plant (dolomite lime doesn't dissolve well). This can be done preemptively every month or so to ensure your soil stays at an appropriate pH.

When you test the pH of your run-off it helps to know what the pH of your fertigation solution was in the first place. When my solution tests very acidic (red) going in, but the run-off comes out as greenish-yellow or yellow (6.5 or 6.0 according to the bottle) then I feel confident that my pH is fine. If it tested anything else or if I was having any problems I could use the aforementioned soil test kit to get a clearer picture of the actual soil pH.

Nullis thanks for this...have to look into these capsules (an idea where to buy them would be great) But I do own a PH meter so I don't know if their an absolute necessity. One thing you said struck me as odd though..you said your fertigation solution was very acidic (which makes perfect sense since when I do add ferts the pH drops like a rock) however your saying it actually comes out higher (or at the very least within the correct range) so in your case when you put in a lower ph (acidity is anything below 7.0 correct?) that it actually goes up..very interesting.

I should also mention that I did indeed add the dolomite prior to putting the girls in their new homes...at least I did somethign right on this whole transplant mess.

i'm having a similar issue but have not yet implemented lime. my issue is that water comes out of the tap at 7.0 and turns the runoff below 5. municipal water supplies vary shitloads by location. imo if you have water that changes 5 points after it hits the soil, lime should definately be used, regardless of whether the change is toward acid or base. the part you mentioned about the runoff being so acidic only when you went "au natural" should be all the convincing you need. sounds like you have less than ideal water and lime is the only way to buffer it. ph'ing the water further alkaline before you douse the plants DOES NOT WORK in this situation and only makes the problem worse. growing in acidic soil is a huge pain in the ass and always hurts the end product. i know this from experience

Total If I'm reading what your saying right then I should just keep using the lime...and NOT buffer the water (either with PH up or PH down) before I add it to the plants..I"m assuming that you have the same feelings re: when adding nutrients to the soil as well...thanks for this.

420Marine said:

Total If I'm reading what your saying right then I should just keep using the lime...and NOT buffer the water (either with PH up or PH down) before I add it to the plants..I"m assuming that you have the same feelings re: when adding nutrients to the soil as well...thanks for this.

Click to expand...

yes you read correctly. of course you still want to ph your fert solution when you feed nutes to get it closer to neutral, but when watering, overcompensating for the ph will cause you nothing but headaches. it doesn't "balance out" in the dirt. from what you've said so far it definately sounds like a water issue and not a soil issue. the lime will keep the water from ruining the soil.

total one last question if I could...do you think I should add more lime (possibly in the next watering) to get the PH to where it needs to be or do you recommend a "top coat" of sorts along the top of the soil? Thanks for being such a good fellow about this....First grow = growing pains

lime takes a little bit to be effective. there's a balancing act between waiting for the ph to even out or adding more (and possibly too much) lime. i'm honestly not very experienced with the top-dressing method of applying lime for potted plants. i've only done it once and they weren't even my plants so i don't have a real feel for how it worked out. a buddy had some plants that were having ph swings and we mixed it in the water and gave the plants a good drink. 2 weeks later (after a feeding and another plain-water watering) the soil had risen almost 2 points. however i was not there during those 2 weeks so i don't know what else may have been going on, and the results seemed pretty drastic. i used to use lime mixed into the soil when i lived at a different address, and i only really used it because it was there and that's what my grandfather always did with his potted outside plants. i wasn't trying to combat any specific issue. even my first grow at this address had lime in the soil because it was what was left over. i never gave it a thought until 2 years later when i'm trying to figure out what the fuck happened to my growing skills.

well it sound like you figure it out pretty much on your own..hopefully I can as well. I did ask the peeps at the hydro store and he said to put about a half inch "ring" around the perimeter of the plant..so I did that and now I"m either going to nute feed tomorrow or just plain aqua...more than likely plain water and see how it stacks up. Again thank you so much for all the helpful nuggets (no pun intended)