Soil Buffering

[KannibisKing]

Hey AFN peeps, Just a quick one..with organic soil mix's such as biobizz all mix, Has PH buffers in it which should buffer the PH for you right?(so no PH pen). What my question is, does these buffers wear off after a while? Like say after 5-6 weeks you may exsperience PH lockout or other issues. Or does it stay bufferd through the whole grow? Thanks for any feedback just trying to work my head around organics, and I only run all-mix this time so I didn't have to worry about PH. Comes out the tap at 7.9 here.

 

[Dr Who]

There are lots of different pH buffers in soil, the main ones are probably clay minerals and organic matter. I believe that if your (soil based) medium starts out at the pH you want, and isn't subject to anything too extreme during the grow then I doubt that you would have any problems.

I don't think that you can "wear out" most of the buffering mechanisms (small lime particles can be dissolved by acidic water, neutralising it, but when they're gone that's it), although some of them may degrade or change over time. If you count the lime reaction as a buffering mechanism then yes you can wear the buffering mechanisms out. I can't think of a comparable mechanism that would resist upward pH deviation similarly (as might be your issue).

Watering with rainwater, although it can be fairly acidic, is good because it has very little buffering capacity of its own, so won't "fight against" the natural pH of the soil. Continuous watering with high pH water, when you are really after a more neutral pH might cause the kinds of cumulative problems that you are talking about. It is possible that if you have very hard water you might be gradually increasing the pH of the soil. A gradual shift to higher pH would probably reduce the availability of some nutrients.

 

[KannibisKing]

There are lots of different pH buffers in soil, the main ones are probably clay minerals and organic matter. I believe that if your (soil based) medium starts out at the pH you want, and isn't subject to anything too extreme during the grow then I doubt that you would have any problems.

I don't think that you can "wear out" most of the buffering mechanisms (small lime particles can be dissolved by acidic water, neutralising it, but when they're gone that's it), although some of them may degrade or change over time. If you count the lime reaction as a buffering mechanism then yes you can wear the buffering mechanisms out. I can't think of a comparable mechanism that would resist upward pH deviation similarly (as might be your issue).

Watering with rainwater, although it can be fairly acidic, is good because it has very little buffering capacity of its own, so won't "fight against" the natural pH of the soil. Continuous watering with high pH water, when you are really after a more neutral pH might cause the kinds of cumulative problems that you are talking about. It is possible that if you have very hard water you might be gradually increasing the pH of the soil. A gradual shift to higher pH would probably reduce the availability of some nutrients.

Thanks a lot for your reply mate, I'm having problems with cal-mag. Micronutrients should be in my soil mix anyway but I still feed cal-mag every other feed. The water is hard water here so I think you may be right with the constant watering with high PH'd water effecting it gradually over time.
Do you have any tips on how to resolve this problem? I've started flushing the medium with Ph'd water. Thanks a lot bro.

 

[Sunny747]

I asked the same question at the hydro store today. They said just to water with lower ph water. I would have thought they'd have a product to adjust soil ph quickly.(with a $25 pricetag... One grower here suggested Aluminum Sulfate to lower PH. Probably worth checking out if it turns into a real big problem. For now I am just dropping my ph water to under 6.0.

 

[KannibisKing]

I asked the same question at the hydro store today. They said just to water with lower ph water. I would have thought they'd have a product to adjust soil ph quickly.(with a $25 pricetag... One grower here suggested Aluminum Sulfate to lower PH. Probably worth checking out if it turns into a real big problem. For now I am just dropping my ph water to under 6.0.

Thanks for your reply sunny, so you think if i lower my PH to 6.0-6-1 for a week or so and keep checking the soil PH that may bring it back down? I will also look into the aluminum sulfate, more organic the better i spose! thankyou brother.

 

[Dr Who]

Hi KK, I think that your simplest solution would be to collect and use rainwater for your plants.

The most realistic alternative is probably to reduce the alkalinity of your tap water by acidifying it, as suggested above. Make sure that the pH remains stable for at least a few hours once acidified, if the pH drifts back up afterwards it won't help much.

I would not recommend aluminium because under the wrong conditions (low pH) this might be quite toxic to the plants and could inhibit root growth. It seems likely that you could get this situation if you are trying to lower pH.

 

[KannibisKing]

Hi KK, I think that your simplest solution would be to collect and use rainwater for your plants.

The most realistic alternative is probably to reduce the alkalinity of your tap water by acidifying it, as suggested above. Make sure that the pH remains stable for at least a few hours once acidified, if the pH drifts back up afterwards it won't help much.

I would not recommend aluminium because under the wrong conditions (low pH) this might be quite toxic to the plants and could inhibit root growth. It seems likely that you could get this situation if you are trying to lower pH.

I have heard rainwater can be quite acidic, one of my buddies on here had problems when he use to water his plants with rainwater because the PH was so low. Is there no other way? Thanks Dr.

 

[Dr Who]

The pH of rainwater is (in principle) about 5.65. It is determined by the level of carbon dioxide in the atmosphere. This pH level is indeed fairly low, but the important thing is that it has no buffering capacity (alkalinity) of its own, so is not able to resist changes in pH which might be caused by e.g. interactions with soil. Provided that the natural pH of the soil is good then rain water will not cause a problem. If the natural pH of your soil is bad then using rainwater won't help it.

Perhaps this is better advice for your next grow than your current one?

 

[steelrat]

Hey KK,

i also live in the UK and my tap water's pH is about 7.8, you know i'm an organic, soil-grower.

Once my water is 'nuted' the pH is 6.8 and the run-off is 6.4.

Plant Magic, the company i buy compost and nutes from do hard and soft-water versions of their compost :

http://www.plant-magic.co.uk/products/supreme.html

Since using their compost i haven't had to worry about pH.

Unfortunately my water provider (Severn Trent) now put chloramine in the water supply, which is chlorine and ammonia, they even tell you on their website not to use chloraminated water in a hydroponics setup !

I'd advise a few tablespoons of dolomite lime in your compost, mix it two weeks or more before planting time, fill the pots with the mix and presoak them to get the micro-organisms going.

With a healthy organic soil mix and average UK tapwater plus your organic nutes your pH should be okay.


All the best,

steely

 

[KannibisKing]

Thanks steelrat, i was thinking of going for PM light mix soil as a guy i knew said he never had problems with the PH in that soil either, be nice to choose from hard/soft water versions too as my water is hard water! I don't even know the difference lol! But i like to try stick with the same brand otherwise u just cant keep up if u get me! All im doing now is flushing my soil because i am having problems with the big SD, so not sure if the soil is locking out all the nutrients because i was feeding her ok and she seemed to be getting burnt on the tips/showing def's so must be a soil problem i stuck a probe in and the soil PH is over 7, so gunna do that then add some Epsom salts i guess to try fix the problem.