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Managing blueberry soil micronutrients

Blueberry bush

My next thorny question was --- how closely can I apply Solomon's soil analysis guidelines to woody plants?  Refreshing my memory of The Holistic Orchard suggests most woody plants might enjoy the same soil conditions Solomon guides us toward.  But blueberries are another matter.

Optimal vegetable garden pH is supposed to be around 6.0 to 6.5, but blueberries like it more acidic --- 4.5 to 5.5, with 6.0 being permissible for the easier-to-please rabbiteyes.  And despite lots of pine needle mulch, pine logs edging the beds, pine humus in the root zone, and even sulfur given to half the plants their first season, the pH in my blueberry patch is 6.5.

Micronutrients and pHWhile 6.5 sounds bad for blueberries, Solomon and Phillips both suggest that higher pH may not be as much of a problem as other writers suggest.  With vegetables, Solomon finds a pH of 7.5 is fine as long as you even out cation excesses, and he reminds us that the pH of our soil may appear much lower to our plants than it does in the testing lab since plant roots hang out around organic matter and organic matter creates pockets of acidity.  (Microorganisms eat organic matter and exude carbon dioxide as a waste product, and the gas mixes with water to form carbonic acid.)  But can blueberries really handle a pH of 6.5 even if the soil has a CEC of 12.6?

The trouble with high pH in the blueberry patch is that it makes it tough for blueberries to find iron, especially if excess calcium is around.  Some sources suggest balancing blueberry soil with less calcium and more magnesium than you'd allow in your vegetable garden, Blueberry iron deficiencyespecially since magnesium can also be hard for blueberries to find.  Luckily, my soil already trends toward low calcium and high magnesium levels, so all I have to do is leave it alone to achieve that goal.

Iron deficiencies are usually pretty easy to see in blueberry leaves during the growing season, as you can see in the photo to the left.  I recall noticing yellowed leaves during the blueberries' first year or two, but not more recently...but I also tend to ignore the blueberries while the vegetable garden is calling my name.  So I think I'm going to table this issue for now and check over the patch once the leaves come back out.  I definitely won't be adding any lime to the blueberries' soil, though, and if I do decide to boost the sulfur levels, I'll do so with ag sulfur instead of with gypsum.

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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The photo you are showing is not an iron deficiency, it is a manganese deficiency, maybe even induced from and iron and aluminum toxicity. A good leaf analysis taken from the leaves next to the fruit will demonstrate my point.

You have no Mn in your soil...

Comment by Michael Fri Oct 7 00:38:07 2016
Michael --- Actually, our soil-test results say that we have plenty of both iron and manganese in that soil...but it's what the plant can suck up rather than what's present that really matters. Both minerals become much less accessible as the soil "sweetens," and leaf symptoms of both types of deficiency are the same. So, it's a bit of hair-splitting on both of our parts to argue whether the picture is iron or manganese deficiency --- likely it's really a bit of both. Either way, though, the root problem is pH, not an actual deficiency in the soil.
Comment by anna Sun Oct 9 15:00:06 2016

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