I carefully measure the Ph of my mix and nutrient solutions. But since I grow outside, occasionally it rains. I set out a bucket and used my Ph meter on rain water and get about 4.2, which is about right for acid rain. Not too surprising since I live 50 miles downwind from an active volcano.
What steps should I take to mitigate this? For small rains I generally ignore it. For large rains I will flush with ro water after, then feed.
Is this correct and is there anything else I can do? Growing indoors isn’t feasible for me. I thought about flushing with slightly alkaline water using PhUp. Is that a good idea?
I’ve gotten some good grows so this doesn’t seem fatal. But recently I had an unusual symptom of bright yellow leaves on new growth. I was wondering if this is a Ph problem from the rain. I was growing 10 plants and it only affected 3. Two recovered almost immediately, but one still has yellow leaves.
The volcano isn’t constantly erupting. About every two weeks it will erupt for about 12 hours. I think I should start measuring the rain all the time and see if I can relate it to the eruptions. Perhaps this is an unavoidable risk. If it doesn’t rain shortly after an eruption, I might not get acid rain at all. Perhaps my good grows were just lucky.
To buffer soil against low pH, incorporate slow-acting liming agents like agricultural lime or dolomite (if your soil also needs magnesium). For long-term resilience, continually build the soil’s cation exchange capacity (CEC) by adding high-quality compost, aged manure, and biochar, which naturally resist rapid pH shifts.
Have you checked the pots pH at the roots yet? Upper yellowing of new growth is iron or zinc. Those are available up to 5.3-7.1. Could you show pictures of the issue, please?
Limestone is the common upward buffering amendment added to increase pH over time.
After prolonged heavy rains, I’d check the pH rather than automatically flushing with RO. Flushing with RO can strip nutrients from the container. Instead, follow the rain with your normal irrigation and feed, allowing the soil’s buffering capacity to do the job.
This is what it looks like. I’ve seen it before, but not frequently. The yellow is almost a fluorescent yellow, like something I wouldn’t expect in nature. All the plants get exactly the same nutrients and mix. If it doesn’t happen much it repairs itself in time.
Fortunately I live in a very dry area and I generally grow autos. It’s entirely possible for me to complete a grow without getting much rain. I surfed the web for answers and it looks closest to a sulfur deficiency to me, but the same web site says it could be a ph issue. For me, sulfur comes from gypsum in the mix. I rarely have the problem, so I doubt if that is it. But I do think a hard rain could be a problem for me.
I grow 10 at a time (the max allowed by the state), but don’t have identical outcomes. Whatever this is, it only attacks plants that already seemed weaker for other reasons. This plant had narrower leaves than the others to start.
That’s iron def showing, like I figured. See how it starts at the petiole and progresses towards the tips? You probably have plenty available, but it’s locked due to pH. Now is that from being too high or too low? Without a current pH number, I don’t know how to advise further.
They gypsum doesn’t effect the pH like lime. It will stay at whatever the pots are without buffering. Limestone would raise it as it buffers the acidity. The thin leaves mean nothing more than that pheno expression leans more to the sativa side of one of the parents.
I’m pretty confused right now. This is what I use to check the mix:
My substrate is too alkaline! It’s about 7.5. When I came up with the recipe, I let it cook for a few days and checked it and it was exactly 6. I’m now wondering if there are acidic components of my mix that are more soluble than the alkaline ones, and they dissolved away over time, making the alkaline components more dominant. Does this happen? I do know that when I planted the substrate Ph was 6.0, and all the nutrient feedings I did were 6.0, but I haven’t been checking the substrate Ph since planting. Clearly I should have been doing that, but it didn’t occur to me that it would change.
Thanks for the help! I was really on the wrong track worrying about the acid rain!
The next question is, what do I do? I can’t redo the mix. Can I use garden sulfur as a top dressing? Will that help? Or should I just boost the PhDown in my nutrient solution and go more acidic there?
I can also do nothing. I still have more than enough very healthy plants to fill my need. I plant extra assuming things won’t go perfectly, but the problem I normally anticipate is pests. I haven’t seen any of those this year so I should be OK anyway.
Cooking takes 1-1.5 mos usually. 6 days isn’t enough time to do much.
I don’t know your mix to judge amendments biodegration, and I’d only be guessing. Soil tends to buffer upwards over time. Usually in veg pots tend to be microbial dominated with a lower pH. As the plants shifts demands to fungal, pH increases.
No doubt. You’re welcome. Happy to help. Luckily your descriptive words made all the difference for me, and we are able to put you on the right track.
Sulfur takes 6+ mos to degrade and change pH, so it’s not a short term amendment.
I’m not a salts guy, so best to wait for better advice. I would drop pH solution down to 6 and test again after a couple days. Then adjust down incrementally from there till in range. @Dman1969@Growdoc@kaptain3d can point you in the right direction from here.
You need to leave some space between your block of text and the amazon link.
Usually I press enter twice to insert two blank lines, then I put in the link.
Thanks! But LOL, the link works but is deceiving. That page has a variety of meters. I had selected the GS2, but the link shows a GS3. Oh well, if I had gotten the link to work at least I would have known to play around with it.
Thanks for looking @Budbrother , appreciate you. @stcapt , you might want to get some citric acid powder and next watering, first make sure your water has enough bicarbonate to ph properly. If it’s low, you can add cal mag to get it to 150-200 ppm and then add your acid to get it to 5.6-5.7 PH and feed that. Give it a day and recheck ph and if getting better, continue until ph drops to 6.5 or very close. Other options include flushing, but I hate flushing soil unless it’s a have to, but since you are feeding synthetic nutes, it’s an option if the lower ph feeds don’t do it in time. Your locked out of iron like Bud said, likely others as well.
I probably took too many liberties. I started with the Bruce Bugbee video on maximizing yield. That mix is 50% peat, 50% vermiculite, 1.4 g/l of dolomitic lime and .35 of gypsum. But I messed with it.
I wanted more drainage, so first I replaced half the vermiculite with perlite. Then I added 1.4g/l of wollastonite. I got the wollastonite from a reddit group on the bugbee method. It seems like he added that after the video. The goal seems to be to increase the silica and since I had replaced the vermiculite that seemed important.
I had trouble getting the fertilizer he recommended so talked to jrpeters, and the csr there told me it was a bad idea to use it for cannabis because it doesn’t have calcium. I did get a bag of the fertilizer eventually, but I found out Professor Bugbee assumes Utah tap water which has plenty of calcium and magnesium. I switched to RO water because we don’t have much calcium and magnesium in our water here but we do have salt. The high salt concentration makes it hard to start with our tap water because I would start out with more than 500 ppm of sodium chloride. Starting with RO water gets me back to 0 ppm, so I can add calmag to my nutrient solution. I also add potassium silicate, per the same reddit post. I have to add a very small amount of PhDown (1ml per 5 gallons of water) to get to a Ph of 6.0.
I looked at the Jack’s peat lite guaranteed analysis and it seemed like I was short on iron. I added azomite and basalt to my mix to increase the micronutrients. I used the concentration the google AI thing told me, which was 0.7 g/l of basalt and 0.35 g/l of azomite.
When I put it all together it came out slightly alkaline, so I added a small amount of garden sulfur (.6 g/l).
All this together comes out to a Ph of 6. But I easily could have made a dreadful mistake. Did I do something stupid? For the most part it seems to be working, other than the upward drift of the Ph.
The sulfur will drop ph, but it will take months to break down, also your soil should have cooked much longer. I think if it were me, I would buy soil if you aren’t growing tens of plants, Roots organic from HD ships right to your door, and it’s PHd for cannabis. Budbrother posted it earlier in another post, he just bought more.
No wonder your pH is high now knowing your mix and info, it’s not surprising you’re having elevated pH given the amount of duplicate liming materials used like dolomite plus wollastonite (Ca + Si sources), plus irrigation water calmag and then added potassium silicate every watering (pH up). Then there’s the gypsum Ca interactions. Added raw S and that binds to Ca sources as it gets converted and oxidized by the microbes forming a less available form of gypsum. That small amount will be neutralized quickly. Wow organic head spin mane. I just laid down a hash joint.
Now the Bassalt and Azomite have barely given a trickle. Those are long term amendments. Usually you build soil with much higher amounts to mineralize it. In this case the amounts stated were intended for, maybe a microbial energy source? Breakdown times weren’t considered by the advisor.
Sometimes RO is a necessity. This lacking Fe part is corrected with your salts when pH is in range again. You have plenty available but can’t access currently.
Things should be easier to get down into range once you stop adding potassium silica every time, just for now. Let that pH down get you down to 6.5. Add just as much calmag as needed to get accurate readings only. You actually changed a lot more than you’d think.
Thanks for the tag My BudBrother. And I’m set to watchin. I’ll be in the back if you need me @stcapt
And your in the best hands with @Budbrother & @Growdoc
for the tag My BudBrother. And I’m set to watchin. I’ll be in the back if you need me 
Plant Whisperer 
