What Is pH
A pH reading is a
measurement of the acidity or
basicity of a solution.
The pH range is 0 (most acid)
to 14 (most basic). pH
represents the number
of hydrogen ions in
solution. The scale used to measure
pH is a logarithmic
scale. Each increment of pH
has 10 times more
hydrogen ions that the previous
increment. Therefore, a
substrate with a pH of 5.0
has one hundred times
more hydrogen ions than a
substrate with a pH of
7.0. pH represents a balance
between hydrogen and
hydroxyl ions; the lower the
pH, the higher the
concentration of hydrogen ions
relative to hydroxyl
ions. Conversely, the higher the
pH, the higher the
concentration of hydroxyl ions
relative to hydrogen ions
Each plant species has a preferred pH; in general,
the optimal range for
maximum growth is 5.4 to 6.8.
Plants experience pH
through the roots. The substrate is a mixture of water with dissolved nutrients,
air and solid particles.
How does pH affect
plants
Plants need light, carbon
dioxide, water and mineral
nutrients in order to
produce sugars (food) and
grow. Water is supplied
through the substrate, and it
contains dissolved
mineral elements. The mobility of
these nutrients is
determined by substrate pH. Especially
affected are those nutrients that plants require in small
quantities, called micronutrients
or trace elements. When
the pH is too low,
the micronutrients become
more mobile and are
absorbed in excess of
what the plant needs, resulting
in this potential for
toxicities. When the pH is too
high, the micronutrients
are less mobile and the plant
cannot absorb enough,
which results in deficiencies. As evidenced by the chloroticgrowing tip and young
leaves, this plant is
experiencing some sort of
nutrient deficiency. This is
typical symptomology of a
pH-stressed plant.
