Measure pH directly in soil or from run-off water?

J

Jupiter79

New Member
Hello everyone!

I'm into my 2nd grow and have some issues with the measuring of pH-value. I can't understand whether to measure it directly from the soil or to measure the run-off water. I have tried both and get different values, and I'm not sure which one to go by. Because there are different opinions (So I've heard, according to the many threads I've read on this) if one should actually measure the soil or the run-off, this gets extra confusing.

Let me just quickly describe the background situation: (I hope it's not too long and deatailed, but maybe someone can pick up something I'm doing either wrong or right)

When I first suspected that the pH could be a little off, I got a "Hanna Combo pH&EC"-meter and measured my tap water which I use for watering and it has a pH-value between 7,9 - 8.0. The soil I'm using has a pH of 5,8
Then I measured pH from the run-off water from one time when i flushed those ladies, and the pH was really low, something like 5,1 or 5,2.
Also one other problem I have is that I water my plants once everyday, and therefore don't use that much water each time. So there is very little or no run-off water to measure. If I have to give more water just to get more run-off water they're gonna get so overwatered instantly.

Anyhow I started to go by the run-off water value and increased the pH with a pH+ solution. And because of the lack of run-off water in my environment I started to measure the pH in the soil instead. After a while I felt like I started to get the hang of the amount of pH+ to use and I ended up with a pH of around 6,5 when measured from soil. So I was happy.

(I don't know if I measure it correctly in the soil, but my method is this: I water the plants and instantly take one sample of soil and pack it onto and around the pH measuring probe on the pH-meter. I've read somewhere that the soil has to be wet when you measure it otherwise the values will be uncertain.)

I thought I had this in the bag, but the other day I slightly overwatered one of the plants and some run-off filled the tray of the pot. So I measured it and this time it was HIGHER than before: 7,8 (from plain water) and 7,2 (from water WITH nutrients). So all this time I used a pH+, should I have used a pH- instead? I am also confused of why the pH of the run-off showed such a low number like 5,2 the first time and next time it shows 7,2-7,5. The only difference I can think off is that when the run-off had a pH of 5,2 it had already been flushed for like a half hour so a lot of water had ran through. The other times I just watered them and a little run-off came through the pot. Could this somehow affect the value? Then again maybe its a just shitty ph-meter?

Conclusion: If I measure the soil it tells me I should use pH up but the run-off water indicates a pH down. Eventhough the soil pH is fine (6,5) I feel like the pH is still off and blocking the plant from absorbing all the nutrients, and it makes me suspect that maybe the pH of the run-off water is the accurate one. But since I got those different readings from the run-off water I don't know what to do.

I didn't mean to get so scientifical and detail-oriented, so sorry if anyone got bored. Just wondering if anyone can be of any help. And any shared thoughts on this will be appreciated.
 
"I water my plants once everyday, and therefore don't use that much water each time. So there is very little or no run-off water to measure."

That may be your problem. You need to have run off to flush out build ups. I would let them dry out thoroughly then flush with
plain water, lots of water. 3 or 4 times the pot size. Then let them dry well before feeding again.
Give them more water each time but less often.
 
Get some garden lime or dolomite lime in your soil as a top dressing mixed 2 inch down and just water. I never pH soil grows or have run off for that matter. My soil mix keeps everything in check for me. I haven't checked yet and my girls are super green and healthy.

Run off like oldman said just empties soil of it goodness and needs to be fed again to regain it. I water every 10 days as my mix holds it well with all the animal poo in there. Again like oldman said let them dry out between feeds so they arent over watered. I have a very good soil mix running now in my journal linked below. You may want to check it out, the soil is doing great and im over a month , just and they have only had water the whole time and 1 time molasses to feed my microbe army!

Hope this helps mate. Keep the ph pens for coco's and Hydro's. Get a good soil mix and F them off. Mine is collecting dust now.
 
I agree with oldman60 and JBC on their response, but I'll add my own response from current experience :). I am using Fox Farm Ocean Forest Soil and General Organics Nutrients (The GO Box (Bio-Series)) with R/O water (bought in 1g jugs from store since I don't have an R/O system). I have not pH'd once this grow, have had absolutely no issues with anything. I've heard numerous times if you go organic, no need to pH, turns out it is true (obviously, it's working for me and has been for just about a month). Last run I ran the same soil but with synthetic non-organic nutrients, the Fox Farm line. I never pH'd run-off except once during flowering and it was in the mid 6 range, although i pH'd the water EVERYTIME (when feeding I'd pH after adding the nutrients). Really hope this helps, always remember there are numerous ways to succeed in growing, just have to find your sweetspot. :)
 
jz1990 said:
Really hope this helps, always remember there are numerous ways to succeed in growing, just have to find your sweetspot. :)
Click to expand...

Thanks for all the replies, but so far it didn't help much unfortunately. Like you said everyone has their own sweetspots in growing. I like to water everyday or every other day. I'm currently using Green House Seeds nutrients and you should feed the nutes only every other watering. If I water everyday, that means the plants can get nutes every other day. If I should water them less, once every 10 Days it means they only get to feed once every 20 days, why would you wanna give them that little? If I do that in my grow setting the plants are really gonna starv. Maybe we have different lighting, temperature and humidity conditions that plays a part here?
I personally think that less frequent (and therefore also more amounts) watering just adds even more to salt build-ups in the soil, just because of the sheer amount. It's like a human, it doesn't matter if you eat 3 times more than what is needed, your body is just gonna absorb the amount of nourishment it needs and discard the rest. It feels to me that if you water frequent and less it gives the plant more chance to absorb everything (or almost) and therefore less amount is left for salt build-ups. And also it's easier to control how much nutes your giving when watered more frequently, easier to keep track on how much they actually need, it's much more easy to overwater for me if I do it say once a week.

But this wasn't really my question, whether i should water less or more, or more or less frequent, I'm still gonna have to measure the pH don't I? And the question wasn't about: "Should I pH or not?"

My problem is that when I measure the soil it tells me my pH is low, and if I measure the run-off it indicates a high pH. I want to know if I should pH the soil or the run-off, which one is the most accurate or reliable etc.
 
Well soil & coco coir have a buffering effect when it comes to PH !

In fact i would be more inclined to check soil PH than run off...


I use to monitor soil PH over my first couple of grows & don't bother any more as its a load of old bollocks... i use to notice a dip in PH levels after watering with nutrients but with in several hours the PH level of soil was back to normal that being the buffering effect !


Run off seems not very accurate to me as the water/nutrients has just been leached through an enitre flower pot... some of those nutrients will stay with in the soil whilst the run off may pick up excessive salts which may well give you total differnet PH reading than that of the soil...
 
Good info Fuzzy, he knows soil also.

Seriously mate if you water everyday to a level where you get run off , you are seriously going to over water them. If you take oldmans advice and water very little everyday with no run off, then that will work. Like he said at the beginning , either water very little very often or water quite a lot not so often. Its up to you which you choose but both work well.

But you have 4 good soil growers info here telling you that ph in soil doesnt really matter so its up to you mate. I dont have any salts at any time in my soil as its all organic feeds in the soil already as my mix is a super soil. Chelated chem nutes have salts not organics.

Yeah different rooms and different temps make everyone's situation different , but all this advice is very similar if you read it all and we all have decent veg setups. I water very little at the beginning to build a good root system so when they are bigger they will want more water and nutes. My roots are like coco roots mate. seriously!! They are massive and white and all over the place!

Send more info and some pics and we can help better. Setup, medium , the F'in lot mate :) But seriously all this info from all these guys is good advice, like fuzzy said coco is different to soil. But i'd still treat coco like soil just with a flush through every few feeds. But if you flush every feed you will just starve your plant as all the goodness like nutes, fungi and microbes will be constantly washed out leaving the plant constantly dependent on nute feeds.

If you take the advice from good soil growers on this site and not what the nute company tells you to sell their product you will do good. Follow nute schedules and feeds and your plants will hate it.

Check any of these guys grows to see if their advice is bad. It works for us and we been doing it years. The way your saying is bad for me. We all have sig's linked at the bottom of our posts , check them out before you take our advice mate.

Happy growing
 
What I meant was that I don't water them everyday so I get run-off. That will of course cause overwatering. I water them everyday with just the right amount so I DON'T get any run-off or maybe very very little. That leaves me little possibility of ph-ing the run-off so I started to measure the soil instead. But after a few waterings that did generate some run-off I measured that too and that's where the confusing part about ph-ing the soil or run-off started. I've read on different articles, forums etc and a lot of people say the run-off is more safe and many also says the opposite that soil ph is the one you should measure.

The problem with salt build-ups that comes from never having any run-off can be solved by flushing them on a regular basis which I also do. (Say once every 3 weeks)

Sorry, I don't have any photos but I can describe the setup:

1 sq. m growing tent with 7 plants growing in soil medium.
310 W LED-light (eq. to 600 W HPS)
3 x 125 W CFL's vertically positioned
1 normal size osc. fan and 2 smaller clip-ons and a vent.fan (all blowing 24-7)
Temperature varies from 75-86 degrees (depending on hot or cold days, or if it's day- or night time) But most of the time it stays around 80 degrees.
Don't have any climat control installed yet so the variations will have to do for now, would be nicer if the levels were kept more constant though)
Humidity is currently 50-55 % and the ladies is 4 weeks into flowering. Kept it higher like 70-80 % during veg. and gradually lower it as the flowering process proceeds. Planning on keeping it to 35-40 % during the end of flowering)

The tent is located in a closet-room, and is actually a bad place and also very confined with poor air circulation. it's hard to control temp and humidity, but I do it by how much the door is kept open or closed. When closed the temp and humidity rises alot, too much and if the door is wide open it's the complete opposite, very dry and cold. So I have to make it work with something in between.

I don't know if the growing medium brand is of any importance since I live in Sweden and I use a Swedish brand. And many growers have told me that's the best you can find here and that it's actually pretty good. I think it has a nice mix of some coco, peet and bark, but I cant really be certain of it's quality. ph is 5,8 and has a 14-7-15 NPK compund, it also has chicken manure, limb and dolomite and also most of the micro-nutrients so it SEEMS to be a decent soil mix, at least to me)

Finally the nutrients are the Green House Seeds powder feeding. It's a universal solution you can use in both veg and flowering cycle. I'm not sure of it's quality, (not a big fan of this universal thing) since it also was alot cheaper than most other brands. However next grow I'm gonna use Metrop nutrients.
 
Your soil/compost PH is a tad on the low side at PH 5.8 your optimal PH of soil/compost should be PH 6.4 to 6.6 !


Once you have observed the buffering effect of soil ya get borded of checking PH of run off or soil PH... I did.


I use organic nutrients & added them to my tap water which i never checked PH off ! or the final PH of nutrient enriched water & water/feed plants every 3 days... i don't bother checking soil PH now & have not done in the last 8 months of growing such is my faith in organics :peace:

Here's some pic's

0011161.JPG
004957.JPG


The only thing i suggest if using chemical/synthetic nutrients is a bloody good flush every few weeks to prevent salt build ups that would screw around with your PH levels.
 
Thanks Fuzzy Duck for the advice, will try using dolomite lime to raise pH.

That is some nice bud formation you've got there. Really nice job! Is it a ScrOG? (I hope it is, otherwise I'm gonna be jealous)

And I also like the idea of organics. Does anyone know what the good brands are? And also does it taste different? or better? with organics?
 
Jupiter79 said:
Thanks Fuzzy Duck for the advice, will try using dolomite lime to raise pH.

That is some nice bud formation you've got there. Really nice job! Is it a ScrOG? (I hope it is, otherwise I'm gonna be jealous)

And I also like the idea of organics. Does anyone know what the good brands are? And also does it taste different? or better? with organics?
Click to expand...

The girls where grown from clones & where LST trained (low stress training) which i stake the cola bearing branches in flowering to support weight.

I use Biobizz nutrients which are organic based & believe Canna now do organic nutrients also with these brands being aviable in europe they may be aviable in your neck of the woods tho.



A majority of organic MMJ growers do report better taste/smell of their plants when compared with chemical/synthetic nutrients & if flushing was applyed in the last couple of weeks !
 
Thanks man.

I am familiar with the biobizz and canna brands and the others too. But there seem to be a general opinion that organic nutes is not as "strong" or "efficient" as chemical nutes are, but anyhow I think I might try it in the future.
 
Well its the whole organic vs chemical nutrient debate...


Organic nutrients take a little bit of time to become aviable to the plant via friendly microrganism activitie to break them down so that the plants can use them etc.

Very difficult to achieve nutrient burn with organics & that PH up or downs or monitoring of PH is not required.

The only minor problem i've noticed with organic's is that defeciencys take a little bit longer to correct, hardly threatening tho for plant health & do suggest using a good micro nutrient additive.




Chemical synthetic nutrients are formed in a different way & more in a chelated form EDTA, DPTA, EDDHA etc etc which are so much more readly aviable to the plant to use instantly, hence we often see signs of nutrient burn from over feeding or on occassion we see toxicity issue's caused by salt build ups from careless growers not flushing their growing medium or not using a suitable method of feeding/watering to prevent the issue.

Hence a flush may well be required once in a while !

PH/EC levels need to be monitoered daily if using hydroponic system or with inert growing mediums such as perlite/ hydroton clay pebbles etc.

As with a good qualitie brand of compost/soil which is PH buffered & buffering effect, PH monitoring of run off/soil is hardly worth while !



NOTE - Soil/composts can lower PH value towards the end of flowering for a reason yet unknown, but has been observed.



Not really seen any great evidence to support greater yield of organic vs chemical nutrients tho in soil/compost but more related to training method used, size of bulb & strain grown !


Soil/compost grows are considored slower in veg & normally lower yielding when compared to hydroponic systems when grown indoors.
 
Yes it really is, again thanks

I don't fully understand this buffering effect though. Would it be too much to ask someone to explain it in just a little more detail?
 
The buffering effect of soil/composts can only be observed by measuring the PH of your soil before watering, after watering (normally a drop in soil PH) & a few to several hours after watering & the gradual increase in PH returning back to the ambient PH level of soil/compost, this being your buffering effect.


I use a compost which is PH 6.6 by the time i've finshed adding ammendments like most soil growers do, i would end up with soil PH of aprox PH 6.8


Now most nutrients are a little bit acidic in nature with some others in the neutral range of PH.


Now after directly watering my soil PH would drop down between PH 6.2 to 5.8 on average.

But with in a period of 6 to 18 hours the PH would climb back to its normal level with in the soil/compost.


Providing your PH of soil stays with in the neutral range of PH 6 to 7 ya be just fine & any short term flux is hardly worth worrying about.
 
At the end of the day ya gotta think of soil/compost & even coco coir as an ambient PH battery of a self buffering nature !

So that it does not matter what PH value your tap water is or final PH of water once nutrients are included as once applyed to soil/compost/coco their will be a short term flux in PH but will naturally self buffer back to origanil level over a short period of time.


The PH checking of run off is a wasted exercise or the fact you apply so much nutrient enriched water as so that you run off eventually becomes the same is a pointless waste of resources...



The only thing which will mess with the soil PH is the use of chemical nutrients via salt build ups & the failure to flush or use a proper feed/water regime.
 
Hello again. It's been nice to receive these good advice. I have now observed this buffering effect in soil. As I said earlier my soil pH was kept at 6.5 or so, but that was when measuring instantly after watering. Now within 1-2 hrs the pH climbs up to 7.0 (plus minus 0.05).

(The only reason I didn't measure the pH after waiting a while is that I read somewhere that if the soil isn't wet you'll get uncertain readings cause the probe doesn't touch the soil as well as with wetter soil. That and of course the fact that I didn't know about the buffering effect)

Really good information which I'm gonna use in the future, thank you so much!
 

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