1, 2, 3’s of PourThru
The PourThru program is designed for growers to
monitor and manage crops. It involves three parts:
1) a simple technique for measuring pH and electrical
conductivity (EC), 2) charts for recording pH and
EC values, and 3) recommended ranges and procedures
for maintaining substrate pH and EC.
The substrate pH is very important to plant nutrition.
The pH directly affects plant nutrient availability,
especially micronutrients (Fig. 1).
Low pH can result in increased micronutrient
availability which can lead to phytotoxicities in some
plants. For example, a low pH (< 5.8) can result in
iron and / or manganese toxicity in geraniums and
marigolds. In contrast, high pH (>6.2) can lead to
micronutrient (iron) deficiencies in petunias and
azaleas; and boron deficiency in salvia, petunias, and
pansies. Both excessively low and high pH’s should
be avoided in greenhouse production.
Most greenhouse crops grow best at pH 5.4 to 6.2, but
some crops such as azaleas and hydrangeas prefer an
acidic substrate while others such as Easter lilies are
grown at a higher pH.
Soluble salts are the total dissolved salts in the root
substrate (medium) and are measured by electrical
conductivity (EC). A conductivity meter measures
the passage of electrical current through a solution.
The higher the EC value, the easier it is for electric
current to move through the solution. The EC of the substrate provides insight to the nutrient status of the
crop. Keep in mind that not all of the salts measured
by an EC meter are fertilizer salts. An EC meter
measures the sum of all salts in a solution, but does not
provide details about the type or amount of each salt
Excessively high EC values are associated with poor
shoot and root growth. Symptoms often begin on
the lower leaves as chlorosis and progress to necrotic
tips and margins. If the root substrate is allowed to
dry, plants may exhibit wilting symptoms because of
dieback of root tips, which further inhibits water and
nutrient uptake. High EC has also been linked with
the increased incidence of Pythium root rot.
In contrast, when EC values are too low, plant growth
can be stunted or leaf discoloration can result from
the lack of nutrients. Usually nitrogen is the most
typical nutrient deficiency (lower leaf yellowing).
But lower leaf purpling (phosphorus deficiency),
interveinal chlorosis of the lower leaves (magnesium
deficiency), or lower leaf interveinal chlorosis and
marginal necrosis (potassium deficiency) can also
Sampling results are only as good as the sampling
procedure. How to set up a sampling program, which
crops to sample, and the number of samples to collect
are all factors to consider.
Any single crop which makes a large contribution
to the “bottom line” should be included. Examples
include poinsettia, fall pansies, bedding plants,
geraniums, garden mums, or hanging baskets. If it is
a major crop, then include it!
Some crops are more troublesome
than others. Examples include crops which are
sensitive to low pH (celosia, dianthus, geraniums, and
African marigolds), to high pH (pansy, petunia, salvia,
snapdragons, and vinca), to low EC (Easter lily and
poinsettias), or to high EC (African violets, begonias,
cineraria, impatiens, New Guinea impatiens,
pansies, and primula). Consider including these
troublemakers in your sampling program.
Consider taking separate crop
samples if there are variations in the substrate used
(different manufacturers or ingredients), the fertilizer
type (acidic or basic) or rates, or planting dates.
The speed of PourThru makes weekly
sampling possible. Ideally sampling should be done
weekly, but in practice it may not be possible. If time availability is a concern consider selecting the
“Top 10 Crops of Concern” based on their economic
value or if they tend to have nutritional problems.
Divide the crops into 2 groups of 5 and alternately
sample each group every other week.
Plugs should be sampled every 2 to 3 days. PourThru
interpretation standards have not been developed, so
consider using the “Squeeze” sampling method. (For
additional information, see the Floriculture Information
Center, click on the topic: Plugs. Address listed
Number of Samples to Collect.
For routine analysis,
collect and analyze a minimum of 5 individual
pots (or for bedding plants a minimum of 5 cell
packs). As a general rule, sample 5 pots per 1,000
pots of similarly treated plants. Results can then be
averaged for a single “interpretation value”.
• If steps to correct an EC or pH problem have been
taken, then resample those plants weekly. If needed,
sample as frequently as every other day.
• If results seem atypical, consider resampling before
making drastic changes, especially to the substrate
Charts for recording pH and EC values, interpretation
values, and corrective procedures are all
listed at the Floriculture Information Center, click
on the topic: PourThru. That web address is:
PourThru Nutritional Monitoring Manuals are
available from the North Carolina Commercial
Flower Growers’ Assoc. for $15 + postage (919-779-
1. Irrigate your crop one hour before
(Fig. 2a). Make sure the substrate
is saturated. If the automatic irrigation system
is variable, water the pots/flats by hand.
If using constant liquid feed, irrigate as
usual. If using periodic feeding (weekly,
etc.): a) irrigate with clear water, b) test a
day or two before you are to fertilize, and
c) test on the same day in the fertilizing
cycle each time. Consistency is very important!
2. Place saucer under container.
the container has drained for an hour, place
a plastic saucer under the container (Fig.
2b). If testing seedlings in bedding plant
flats, pull out one cell pack and place it in
the saucer (Fig. 2c).
3. Pour enough distilled water on the
surface of the substrate to get 50 ml (1.5
oz) of leachate
(Fig. 2d). The amount of
water needed will vary with container size,
crop and environmental conditions. Use
the values in Table 1 as guides.
4. Collect leachate
for pH and EC
(Fig. 2e). Make sure
to get about 50 ml of
leachate each time
(Fig. 2f). Leachate
volumes over 60 ml
will begin to dilute
the sample and give
you lower EC readings.
5. Calibrate your
pH and EC meters
prior to testing
2g). The test results
are only as good as
the last calibrations.
Calibrate the instruments
every day that
they are used. Always
use fresh standard
Never pour used solution
back in the
6. Measure pH and
EC of your samples
(Fig. 2h). Test the
extracts as soon as
possible. EC will not
vary much over time
provided there is no
evaporation of the
sample. The pH will
change within 2
hours. Record the
values on the charts
specific to each crop.
for all pics and tables please visit https://www.ces.ncsu.edu/depts/hort/f...out%20123s.pdf