buffering up
instead of all of the nutrients going directly to
plants. So, the CEC in the coco is exchanging
some of the K and Na for Ca and Mg. This
exchange is now unbalancing your nutrient
solution, increasing the K and Na while decreasing
the Ca and Mg. How much unbalancing, you ask?
Earlier, I mentioned the coco could have as much as
1.56 g of K and 0.35 g of Na per 100 g of coco. Your nutrient
mix is not highly concentrated with Ca and Mg, but it is
enough to get some of the K and Na released from the CEC.
About 15 years ago, I was growing roses in coco and we
did a weekly chemical analysis of our feed and drain water.
The first time we used coco, we noticed the Ca in our
drain water was less than 40 ppm (we would have normally
expected the Ca to read 100-150 ppm in the drain water),
and we were feeding Ca at a rate of about 200 ppm. For the
next two weeks, we had the same result, so we doubled our
Ca to 400 ppm. The analysis of our drain water went up to
about 50 ppm of Ca. We watched that for about three weeks
and then started feeding Ca at about 500 ppm and still had
very little change in the Ca ppm in our drain water. It took
about four months for our drain water Ca analysis to read
about 100 ppm. The loss of the Ca and Mg is one thing, but
you also get an increase of K and Na. High levels of K will
hinder the uptake of Mg by plants. Sodium can negatively
impact plant health even at low levels and is toxic to some
plants starting at 50 ppm.
“Sodium can negatively impact
plant health even at low levels
and is toxic to some plants
starting at 50 ppm.”
The widespread use of calcium and
magnesium supplements in the indoor
gardening industry is an indication that many
have experienced the CEC phenomenon
in coco that I am talking about here. The
deficiencies are observed and can be
corrected to a certain extent with calcium and
magnesium supplements, but there are also
coco products out there buffered to a higher
level, which don’t need the calcium and
magnesium supplements.
94
Maximum Yield USA | April 2015
A Coco-Buffering
Glossary
Cation Exchange Capacity (CEC) –
The degree to which a growing media
can adsorb and exchange cations. The
value of a cation exchange capacity is
normally expressed as meq/100 g.
Cation –
A positively charged ion, such as Ca++,
Mg++, K+, Na+, NH4+, H+, Al+++.
Milli-equivalent (meq) –
A measurement often used in
quantifying a cation exchange capacity
(meq/100 g = milli-equivalent per 100 g
of dry media). The milli-equivalent is
based on the value of an equivalent. An
equivalent is the weight in grams of a
molecule divided by its molecular weight
multiplied by its charge. For example,
hydrogen (H+) has a molecular weight of
1 and a single positive charge, so 1 g
of hydrogen is one equivalent. Calcium
(Ca++) has a molecular weight of 40 g
and a double-positive charge, so 40 g
of calcium is two equivalents.