I killed a blueberry shrub once, with too much acid. First it wilted, and then it turned brown. I will see pH values as low as 3.8 once in a while, and this makes me nervous, but so far, the shrubs seem to be OK. When I get a low value like that, watering the shrub with our city supplied cold water, pH = 7.6, seems to take care of the problem.

Thread linked below shows pictures of my pH ~3 blueberries. They didn't look chlorotic. Rather they didn't grow, very unthrifty, small leaves, and branches where leaves fell off. Roots didn't grow either. I've since repotted but too soon to see if they'll take off growing.

Here is a link that might be useful: low pH blueberry

Blueberries can be fussy beyond the issue of pH. I have had difficulty establishing them at one site with an excellent clay loam "bottom land" type soil- even on raised beds, although the pH is around 5 after sulfur. Ended up adding a ton of sand and removing much of the native soil and replacing all but two of the plants, which for some reason thrived.

In the wild I've seen them flourishing in a similarly heavy soil, so I have to say I'm a bit mystified. Perhaps some varieties are more tolerant of clay. Chlorosis is often also caused by poor drainage.

Thanks, everyone. I actually had your recent post in mind when I started this thread, fruitnut, since your plants didn't show any signs of chlorosis. In contrast, I'm definitely seeing chlorotic leaves in quite a few of my potted plants (always new growth, not older leaves) in conjunction with pH readings somewhere between 3.5 and 4.0. It definitely looks like the kind of symptoms you'd expect to see if the pH was too high. Interestingly, I see more chlorotic leaves on my rabbiteye bushes than on either NHB or SHB. On most, it comes and goes, and it's never severe. I do have a few plants that have been a but stunted, though, so I'm wondering if the low pH is responsible.

How confident are you of your pH reading? Anymore I don't trust pH meters, not the ones I have anyway.

Also I second HM observation, if your potting mix water logs that can cause chlorotic leaves.

Pretty confident -- my General Hydroponics test kit (dye indicator) suggested that the pH was at or below 4, so I bought some bromocresol green to double check and get a more accurate reading. The latter put the pH under 4 but above 3.5. I'm also reasonably sure that it's not water related. They're all in bark based mixes (70% to 90% aged pine bark) and fabric pots that drain very well. That being said, I observed the worst bout of chlorosis this spring right after a day of heavy rain. Even so, the roots should still have had plenty of air given the porous mix and pots.

To provide a bit more context, this has been an off and on again problem for me over the last couple of years. Last year, I discovered that I had what appeared to be a bad batch of pH test strips, and I switched to the GH test kit mentioned above. It strongly suggested that I'd been adding too much vinegar to my irrigation water, so I backed off considerably (to 1 tsp per gallon). I never fully trusted it, though, which is why I bought the bromocresol green. Now that I've done pour through tests with the latter and gotten similar results, I'm much more confident about the readings. What's curious is that I've never added sulfur to my potting mix (bark/peat/perlite) nor sulfuric acid to my irrigation water -- just vinegar. My well water isn't especially high in bicarbonates, and the pH tests right at neutral to maybe slightly acidic. Perhaps vinegar has more staying power in my particular circumstances? I've always operated under the assumption that its effects are temporary since organic acids are metabolized by microorganisms, but there's got to be some explanation for what's going on here. Of course, there could still be something that I missing or misunderstanding, but the dye indicator appear to be quite clear. So far, I'm basing my conclusions on pour through tests on two pots. Perhaps I'll test a few more today...

This post was edited by shazaam on Mon, Jun 30, 14 at 7:30

My guess is it's not low pH. Something else is going on. But if the plants are growing well and chlorosis is just temporay, I don't see an issue.

No, I haven't observed chlorosis from low pH, but I have a couple thoughts.
"What's curious is that I've never added sulfur to my potting mix?Not even ammonium sulfate?

Where I have read most about chlorosis in relation to low pH is in soils where Aluminum is present - which seems unlikely in your pots - unless your water or something else is adding it.

More likely applicable to your situation is a comment in Spectrum Analytic's document on fertilizing blueberries. In discussing symptoms of Potassium deficiencies, it is stated: "Less frequently, younger leaves may develop interveinal chlorosis similar to iron (Fe) deficiency." And, as pH begins to drop below 5, K availability significantly drops off.

Page 2 of http://berrygrape.org/files/newsletters/blueberry/2006-06.pdf is an interesting read regarding dropping pH in the root zone.

Thanks for the link, charina. I thought that I'd read about iron chlorosis in low pH soils somewhere at some point in the past, but my more recent searches hadn't turned up anything. I agree that aluminum seems unlikely to be the culprit in this particular case, but that was interesting reading nonetheless. It had crossed my mind that the chlorosis might be induced by a deficiency other than iron, so a potassium deficiency sounds reasonable. I'll look into that possibility. Finally, your point about a ammonium sulfate is a good one -- my soluble fertilizer of choice for the last year or so has been Jack's Classic Acid Special, which derives its nitrogen from...ammonium sulfate. I've always been under the impression that acid forming fertilizers don't have a big impact on pH, but the cumulative effect over time might be more significant than I realize. I don't use a lot of it at once, but I'm in the habit of applying it weakly (1/4 tsp per gallon) at every watering, which, in the summer, is 3-4 times per week.