Page 16 - Griffin Gazette Spring 2016

Media pH- Keeping the
Green Springin
By Rick Yates,
GGSPro Technical Services Manager
Gorgeous spring
flowers deserve a
canopy of rich, healthy
foliage supporting
them. Foliage color
can serve as a useful
indicator of overall plant
health. Several factors
most commonly impact
foliage color. A root
system compromised
by disease will quickly begin to diminish
the appearance of the foliage. Nutritional
imbalances also produce foliar symptoms
that warrant further investigation. Maintaining
the proper media pH goes a long way towards
averting nutritional deficiencies and toxicities
that manifest as sub-par performance and
appearance. Fortunately, several effective
tools can be used to manage media pH.
Media pH is a dynamic system with several
variables that need to be managed well to
produce crops that meet their potential.
Some of the factors that have a bearing on
media pH include: soilless mix components,
alkalinity of the irrigation water, fertilizer inputs,
limestone type and amount and, in some
cases, the plants themselves. Many plants
exert influence over the pH of the media
16 Griffin Gazette Spring 2016
they're growing in, sometimes in a direction
that seems contrary to optimum growth.
It's worth taking some time to explain why
media pH plays such a big role in the nutritional and pentas. If these crops were to be grown
well-being of the crops we produce. The
availability of nutrients available for uptake by toxic levels of micronutrients. Most of these
plants is influenced by the pH of the media.
Micronutrients, such as boron, copper, iron,
manganese and zinc, become more available
as the media pH declines. In soilless media,
availability of these elements is good up to
around pH 6.2 with declining availability as
the pH increases further. Molybdenum is
unique in that it becomes more available as
soil pH goes up, as poinsettia growers know.
You might wonder why we don’t just grow all
crops except poinsettias at a low media pH to
maximize the availability of micronutrients. The
answer is revealed through a discussion of the
relative ability of different plants to scavenge
for micronutrients. Some plants are inefficient
at taking up micronutrients, especially iron.
Examples include some of the most popular
spring flowers, such as calibrachoa, diascia,
pansy, petunia, snapdragon and vinca
(flowering). For these crops, we generally
strive to provide a media pH in the range of
5.3-5.8 to make the micronutrients readily
available for uptake. Another group of plants
are over-achievers when it comes to taking up
micronutrients: examples include geraniums
(seed and zonal), helichrysum, impatiens
(New Guinea), lisianthus, marigolds (African)
at a pH of 5.3-5.8 they may well accumulate
crops will thrive at a media pH of 6.0-6.6.
Now that the importance of media pH has
been established, the next step is to consider
how best to keep it in the correct range for
each crop. Most growers produce a variety
of plants with varying pH requirements in
the same growing area. Success has been
achieved growing low-pH crops (5.3-5.8)
with those that are not as particular, targeting
a middle ground (pH of 5.7-6.2). Whenever
possible, segregate crops that need a higher
media pH (6.0-6.6) and grow them together.
Varying temperature and light requirements
may not always allow that to happen, so do
the best that you can.
So-called high-lime soilless mixes may be
an option when high-pH crops cannot be
segregated. These mixes receive a higher
lime charge with the idea that the high-pH
crops can be fertilized along with the lower-pH
crops while maintaining a satisfactorily high
pH. Another option is to simply fertilize the