[nafex] blueberries and pH, etc

Alan Haigh alandhaigh at gmail.com
Fri Dec 21 15:27:47 EST 2012

As I understand it from long ago research in soil text books, gypsum is
only affective in sodic clays and not as an all purpose panacea for
excessively clay soils.

>From direct experience, I have found the need of low pH is exaggerated in
blueberry cultivation and I've several times seen vigorous and productive
blueberry stands in soils with a pH near neutral where plants were annually
mulched with wood chips and even Sweetpeet.  I suspect the humic acids
released in the decomposition of wood may free up adequate iron which is
easily absorbed by fine roots that tend to form in the interface of soil
and mulch.  There is established research by Carl Whitcomb that alkaline
induced iron deficiency can be alleviated by only a surface application of
sulfur well before any but the soils surface experiences any reduction in
pH.  This was with pin oaks in unmulched soil.

I've also found that pine needles do not appreciably lower the pH of soils
and have compared soil mulched with pine needles for years to nearby
unmulched soil with both having identical pH.  Conifers due absorb less
calcium than deciduous trees as a general rule, which may somehow be the
source of this old gardening husband and wive's tale.

Treating water with sulfuric acid is probably too much work for the casual
grower but I've heard vinegar is comparatively useless from experienced
growers who've done the research as it's acidity is lost within moments of
contact with soil with very little adjustment.   Seems to me an annual
application of pelletized sulfur would work to counter alkaline water.

I have read numerous testimonials that peat moss bales is an affective
place to grow blueberries in the west, even where irrigation water is
alkaline. I think one reason they work in the west is because it doesn't
rain there much during the growing season, otherwise I suspect there would
be drainage issues with a pure peat mix and blueberries suffer from poor
drainage as much as any plant I've grown.  Also, establishing plants often
suffer from drought as their roots are not very efficient.

Anyone with questions about growing blueberries in alkaline conditions
should post a question on the Gardenweb as there are a few very serious
blueberry growers in high alkaline soils that participate in the Fruit and
Orchards section of that site.

"Lee is right, Gypsum (calcium sulfate) is a neutral salt and in most
circumstances has no effect on soil pH.? There have been some reports of it
raising pH in soils that are high in aluminum, but this is attributed to
increasing the solubility of aluminum in these soils. Gypsum can be
beneficial or detrimental depending on your soil, but it is often most
useful for breaking up heavy clay soils and displacing sodium (by replacing
it with calcium)?in soils with excess sodium. Depending on the composition
of your soil, it may in fact lower pH very slightly but this is also
specific to certain soils and generally it must be applied at high rates to
have this effect.
Blueberries need acid soils (pH 4.5-5.5) for two reasons.? One is because
they have poor nitrate reductase activity.? As soil pH is reduced, nitrogen
is more commonly found as ammonium, which blueberries are able to take up
and utilize.? At higher pH, soil nitrogen is?oxidized into nitrates, which
blueberries are very inefficient at utilizing for growth.? If using
conventional fertilizers for blueberries (i.e. if NOT using soybean meal as
suggested earlier) then one should use either ammonium or urea, depending
on your objectives. The other reason why blueberries need low soil pH is
also because they often have problems with iron deficiency in higher pH
soils.? As soil pH rises, iron becomes less bioavailable (as do zinc and
manganese, although these are less problematic in blueberry).? Blueberries
grown in soil that is too high in pH usually develop iron deficiency before
they experience nitrogen deficiency.? Iron deficiency in blueberries
 manifests itself as a yellowing of the leaves with some green retained at
the midvein and in some of the other leaf veins, leading to what many
people refer to as a "Christmas tree" pattern.? Google "Blueberry iron
deficiency" and you will see many good pictures.? Many people see this
yellowing and assume it is nitrogen deficiency?so they never really fix the
problem, or worse, they burn the plants by giving them too much or the
wrong kind of nitrogen, as blueberries are very sensitive to high EC.
Adding elemental sulfur about 6-12 months before planting is the best way
to lower soil pH (the rate is?dependent on the amount of lowering needed
and your soil type).? This is because soil microbes break down the sulfur
over time and it gets converted into sulfuric acid.? The effect is
temporary, so you should monitor soil pH every year or so to make sure it
stays in the proper range.? Fertilizing blueberries with Ammonium Sulfate
provides the correct form of nitrogen and has the effect of lowering pH
slightly at the same time (although to a lesser extent than adding
elemental sulfur).? This is the recommended nitrogen source for established
blueberry plantings where the pH has started to creep upward.? Urea has
less effect on soil pH and is the preferred nitrogen source for blueberries
where the soil pH is already in the correct range.? There is some evidence
that high organic matter and mycorrhizae may help to mitigate nitrogen
issues when soil
 pH is higher than optimal,?so that blueberries can get sufficient
nitrogen.? Unfortunately, this doesn't fix the iron deficiency that occurs
in many soils when pH is too high, so it can't be counted on as a way to
grow blueberries in higher than optimal soil pH at every site.
Of course everything I just said mostly applies to growing blueberries in
the ground.? If you grow in pots or bales of peat, there may be other
issues with the soil chemistry which affect how well blueberries perform.

Michael Dossett
Mission, British Columbia

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