Midflower pH Issues

So, I'm three weeks into flower and my soil pH is 7.2, and it's climbing.

At transplant (about a month ago), pH was about 6.6 or so. Two weeks ago, pH measured about 6.9-7.0.

The trend is increasing, but what can I do about it at this point? I'm watering with RO that's about 7.5pH, should I start bringing pH down when I water? If so, what's the best thing to use to accomplish this?

It's odd because I mixed up more soil than I needed for this cycle and the unused soil is at 6.7pH. So, something is going on in these containers. I'm assuming this soil is bacterially dominated and large amounts of P is inaccessible without solid fungal activity.

Plants are looking good at the moment, but I'm sure yield is going to suffer...and if pH continues to climb I'm thinking things could make a real turn for the worse.

Any thoughts?

*bump*

I suppose my options are:

A) Let it ride, there's nothing you can easily do to correct this mid run.
B) Try and amend to bring the pH down, but you risk causing other issues in doing so.

Thoughts?

What are you using to test the ph?

Using the Blue Lab soil pen...which I've been calibrating often to make sure the readings are trustworthy.

Ok well that answers my only Q; a soil probe should be fairly accurate. They look so healthy its doubtful you have lockout issues....even if your soil is 7.2 ph that should be ok; still in range.
Adding some organic matter like compost via a top dress can help drop the ph a few points. Was just reading that watering with cold coffee can also help but I certainly wouldn't do anything too drastic for these plants.

Thanks for your input RD, I've enjoyed your threads. I think you follow the TLO grow style? That's what I've got going here. Things are going well besides the pH issues.

Good call on the topdressing. I topped with insect frass and EWC about 10 days ago. Things have certainly improved since then...but the pH continues to climb. The cold coffee idea is interesting, going to give it some thought.

Yep TLO changed my life in a very profound way. Now I eat healthier and even started growing my own food...
I would think that just like everything else in organic growing the compost you added will take time to work. The coffee being already soluble is supposed to be more expedient but also temporary. Ph in soil fluctuates constantly so I really wouldn't worry about it too much; your plants look great. If you didn't have that fancy schmancy digital meter you wouldn't even know your ph was jacked...

Richard Drysift said:

If you didn't have that fancy schmancy digital meter you wouldn't even know your ph was jacked...

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Hah...there's truth here.

Yeah RD, the TLO book was a real eye opener for me as well. Now that I've spent more time researching and learning organic growing methods I'll be changing things up from the Rev's approach. But it's been a huge, huge step in getting things going with soil.

Love that you've transitioned into producing your own food, that's in my future as well.

EWC and Compost doesn't necessarily bring the PH down. My compost and EWC is in the 7.5-8.5 Range infact. I would say your plants look really healthy, so don't worry if its not in the perfect range. Drastic PH changes can shock the microbial soil food web that exists because of the PH your in. Instead focus on adjusting your next mix to address this. so add less DL, more gypsum, or add some sulfur. Or add more PEAT which has ph of around 5. For this current run you can adjust your water to 6.5, give it a bit of a short term swing and at least not raise the ph of your soil.

Strudelheim said:

EWC and Compost doesn't necessarily bring the PH down. My compost and EWC is in the 7.5-8.5 Range infact. I would say your plants look really healthy, so don't worry if its not in the perfect range. Drastic PH changes can shock the microbial soil food web that exists because of the PH your in. Instead focus on adjusting your next mix to address this. so add less DL, more gypsum, or add some sulfur. Or add more PEAT which has ph of around 5. For this current run you can adjust your water to 6.5, give it a bit of a short term swing and at least not raise the ph of your soil.

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Thanks for the reply Strude. I'll have to measure the pH of my EWC, you've got me interested in that now.

What's got me stumped is the unused soil (same mix) is right now sitting at a nice 6.3-6.5pH while the containers are up in the 7s. I'm really curious what would cause the pH in the containers to rise so much over the unused soil. Any ideas? My readings from the Lowenfels 'Teaming' trilogy suggest that my soil is bacterially dominated at this pH. We also know that mycorrhizal fungi, which release the majority of unavailable phosphorus so critical in bloom, require pH in the 6s.

@ShLUbY has said that his yields were impacted with a similar high pH and that once he corrected it, yields rebounded. From what I've read, cannabis can grow well with limited P (as long as it's not too low) and look solid throughout a grow, but during flower, yields are the first thing effected.

It's entirely possible that my soil mix has too much P, which can have a negative effect on myco fungal life as well. And without the mycos, 80-90% of P will remain locked up even though it's in abundance. I just sent my soil out for analysis, so that will tell more of the story I hope.

I plan to recycle this soil. But I'm unsure of the best way to bring the pH down before the next run. I like your idea of adding gypsum, but that will add additional calcium to the mix too. Peat is a good option, wonder how much I'd need to add to get this down to 6.5 or so. Most likely I'll recycle by blending the soil now in the containers with the unused soil and add some peat and possibly gypsum if the soil tests show that calcium isn't too high.

Oh and if I wanted to adjust my water prior to using it, is gypsum a good way to do this?

No gypsum is more of a slow acting soil ammendment. It does raise ph or buffer it alkaline like dolomite lime, thats why i suggested to use it as a replacement for your lime so that the mix stays more acidic. Elemental sulfur is used to lower ph it is also a slow release microbial activated up to 3 months for full effect. 1/4 cup should bring down a cubic foot mix from 7.5 to 6.5 given a month or two. to be honest i wouldnt worry about it that much since your plants are looking fine. just don't add any dolomite lime or calcium carbonates etc into your mix. and check your compost or ewc to make sure its not way up there.

Ah ok, sounds like gypsum is more pH neutral then? I didn't add any suffer, so it's probably a good idea to get some in there anyway.

Here's the mix I followed, more complicated than it needs to be I now realize.

Base mix:
6 gal organic soil mix
2 gal rinsed coco coir fiber
4 gal perlite
4 gal earthworm castings

Amendments:
1/2 cup PURE Grow (Organicare)
1/2 cup greensand
1/2 cup ground oyster shells
3/4 cup crushed oyster shells
1 cup powdered Dolomite lime
1 cup pelletized fast-acting Dolomite lime
1/2 cup blood meal
1/2 cup 9-3-1 bat guano
2 cups feather meal
2 cups bone meal
1/4 cup powdered soft rock phosphate
1/2 cup gypsum powder
3 cups kelp meal
3 cups alfalfa meal
1/2 cup granular Azomite
1/4 cup Humid Acid Ore
2 cups steer manure

For 2 cubic feet of mix thats pretty rich. Looking at your plants thats not a bad thing, might have to take a page out of your book! But like I said for nitrogen you have 1/2 cup bloodmeal, 3 cups alfalfa , 2 cups feather meal.then your 1/2 cup Nitrogen rich bat guano. Not to metnion whatever is in the "pure grow". Additionally kelp meal and bone meal are decent source for some N too. Works out to 7 cups of N, for 2 cubic feet. Maybe all that N is feeding the bacteria which is bringing up ph? But for sure part of it is the Dolomite lime, and Oyster Shell. The reason you might not see a ph change in the stored bin, is because the plants and watering and temps are interacting with it differently. So you can replace oyster and dolomite with gypsum for calcium, and get some sulpomag for the magnesium. Thats what my strategy was. Most of my compost based mixes I made were all coming out at 7.2-7.4 out of the gate. With said changes Im at 6.4 Now, shooting for 6.7.

Remember its the "carbonate" in oyster and dolomite and in hard water that raises ph. Gypsum is calcium sulfate so no carbonate to bring up the ph as a liming agent.

for my calcium ammendment I use just 1 cup per cubic foot. 1/3 Cup oyster shell flake, 1/3 cup gypsum, 1/3 cup dolomite lime. Sulpomag is on back order so this is what Im jusing for now.

a tip from what i've found recently, my RO water was coming out at about 8.0-8.1 pH.... this was without air stones bubbling the res. after adding the air stones, the pH is now around 6.8. Must be some carbonic acid forming in the water to lower the pH. which is fine IMO. still O2 getting dissolved as well. unfortunately the heat is moving in... and I'm gonna pay attention to the pH changes of the res as it warms up. higher temp holds less O2... which means CO2 will likely increase, and more carbonic acid will form.

To lower the pH of the soil, i would definitely consider soil sulfur. the prills would be a good choice. Really slow release as previous poster mentioned. also, i'm holding off on adding organic matter to my recycles until at least 2 or 3 runs have been done. roots break down into OM, biota breaks down into OM, nutrients break down into OM... matter is neither created nor destroyed right? besides pulling nutrients out of the soil, the plant builds itself of atmospheric inorganic carbon, which means your SOM is staying right in the pot, and new SOM is being created with each run.

I just concluded that one of two things happened (or a combination of both) with my mix. 1) I was adding too much SOM at each recycle and diluted the mix too much and the peat moss lost its acidity and was neutralized. 2) the mix turned mostly bacterial, driving up pH, and I need to focus more on fungal teas to try and get a better balance of diversity in my soil. I will be practicing both from now on

also as above poster mentioned, sulfur will acidify at first, but once the sulfur is used up it leaves behind the calcium, which will raise pH. I've already been down that path and learned the hard way haha.

btw, your plants seem to be showing normal growth for 3 weeks. I wouldn't get too drastic. I would brew a fungal tea. no molasses. just compost, and food stock for fungus. fish hydro (according to elaine ingham), maybe some oats, and some kelp. bubble for probably 24-36 hours (if room temp is warm, i'd just go 24. if it's cool enough, 36.

And simply replace oyster shell and dolomite with gypsum on next amendment. that should keep ph close to where it is. I would try that before using sulfur. your not looking for drastic changes, just zoning it in to the perfect range, so I recommend little adjustments, nothing drastic, and see how the next run goes.

Those plants look good to me, I wouldn’t get too caught up with pH in organic unless you are seeing some truly extreme outliers.

Southerner said:

Those plants look good to me, I wouldn’t get too caught up with pH in organic unless you are seeing some truly extreme outliers.

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agreed. the only reason why i had to delve so deep into my pH was because my yields were about 60% of what they should have been. the strange thing was the plants looked amazing.... they were just lacking bud badly.

Pee on them.

That should bring down the PH i dont ever do PH you should be able to look at your plants and tell what they need if anything.