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As Why do blueberries need acidic soil? points out, it seems that iron is really the biggest nutrient to suffer in alkaline conditions. Even an answer there, despite a nice emphasis on the broader soil ecology, ends up focusing on this nutrient:

Acidic soil … to release phosphates, iron, magnesium which your blueberries love. The iron particularly is needed …

Similarly an answer to Is it really important to give blueberry plants acidic soil? quickly introduces a similar claim:

At higher pH, the bushes will have an iron deficiency…

So as much as I appreciate building good soil, I've seen doubts cast that I'll really be able to pull it off to the extent blueberries theoretically need. (E.g. "pine needles aren't really acidic", "sulfur discourages worms and/or mycorrhizal fungi from thriving", "all your irrigation water is going to be alkaline anyway"… I'm not particularly intending to debate those claims here.)

I've got some chelated iron around (HEDTA if memory serves) that I use in my aquaponics systems. It is iron bound to a "helper" molecule such that [they claim] the plant can take in the iron and use it, at much higher pH levels than where iron is normally available.

What would happen if I simply gave my blueberries an occasional foliar application of iron, or periodically top dressed the soil with some of the powder, and didn't worry so much about changing the actual pH of the soil?

  • I'd be interested in knowing this as well. This year I planted my blueberries in the ground without checking the pH and they have not flowered at all. Would be good to know if there's anything I can add to the soil to help them produce or if one must keep them in a controlled potted environment. – Organic May 27 '16 at 20:09
  • @Organic My actual strategy for blueberries so far has been liberal application of coffee grounds around my blueberries, and honestly I hope that is a better idea than this. (Haven't been at one house long enough to decide if it is working.) But even though I'd prefer to avoid "fake stuff" outside, even if it is OMRI-listed or whatever, I've always been curious about this :-) – natevw May 27 '16 at 20:16
  • As anyone can tell you, gardening is about building the soil correctly for the plants. If you don't want to do this, then grow the plants hydroponically. – Graham Chiu May 27 '16 at 21:39
  • @GrahamChiu: Absolutely, but I guess my question is: what if I'm in a situation where I can build what would be "great soil" for all sorts of other plants, but that soil has a pH of 7 or 8 or maybe even 6 … but still a far cry from the 4.5 that blueberries are supposed to need. In otherwise good soil, could chelated iron replace the need for such an impossibly low (given my soil/water) pH, so to speak? – natevw May 27 '16 at 23:30
  • If it's impossible to amend the soil, then pull the plants out and put them into a container where you can control the plant's requirements more easily. – Graham Chiu May 27 '16 at 23:52
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You could apply a foliar spray of chelated iron once or twice a season, but that's not fixing the problem which is the soil pH is not allowing the plant to access the nutrients in the correct proportion. It's very unlikely to see iron deficiency in soil itself, and like you, I have chelated iron on hand for my aquaponic plants which do get iron deficiency.

I only water my blueberries using rain water (neutral) or from my various aquaria so that the water tends to be a bit acidic.

So, you might be able to (inefficiently) correct iron with a foliar spray but what about the others?

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The crux is that its not just about the amount of iron in the soil. It has to be in a form that the plants can absorb.

Plants mainly acquire Fe from the rhizosphere. Although Fe is one of the most abundant metals in the earth's crust, its availability to plant roots is very low. Fe availability is dictated by the soil redox potential and pH. In soils that are aerobic or of higher pH, Fe is readily oxidized, and is predominately in the form of insoluble ferric oxides. At lower pH, the ferric Fe is freed from the oxide, and becomes more available for uptake by roots.

Joe Morrissey, Mary Lou Guerinot,
Iron uptake and transport in plants: The good, the bad, and the ionome

Your best bet may be to either grow in a container or a buried tub since correcting the PH aggressively with sulphur will harm microorganisms. And lime will leach from the surrounding soil which will raise the PH gradually anyways. You may be able to find a used bathtub or plastic barrels used to ship cheap wine and grape juice.

Keeping the PH low can be done by adding organic matter and mulches which are low in ph. With peat moss from sphagnum being a popular choice since it has a very low PH. Bear in mind though that peat bogs store large amounts of carbon and clearing and draining bogs for mining releases huge amounts of greenhouse gasses as well as deprives many endangered species of their habitat.

Providing nutrients by way of chelated iron and other supplements is going to be very expensive. You need far more than in a hydroponic system.

There is aslo a very good chance that the plant roots may not be able to thrive in an alkaline soil anyways since they have spent millennia adapting to peat bogs.

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