Page 20 - Griffin Gazette Spring 2016

Testing Media pH and EC with the Pour Thru Technique and potassium bicarbonate. All three offer proven performance,
(Adapted from Cavins, T.J.; Whipker, B.E; Fonteno, W.C.; Harden, providing fast acting increases in media pH. Flowable limestone, sold
B.; McCall, I. and Gibson, J.L.; 2000. Monitoring and Managing as Limestone-F, will raise media pH and hold it at the new level for a
pH and EC Using the Pour-Thru Extraction Method. North Carolina longer period of time compared to potassium bicarbonate. However,
State University. Horticulture Information Leaflet 590.) because the solution is quite thick, flowable limestone is more difficult
to apply. While it can be applied using an injector, it is abrasive and may
Materials Needed cause premature failure of wear-related components. Some growers
• Distilled water prefer to use a simple siphon system, such as a Hozon. Treatment
with Limestone-F also contributes significant amounts of calcium and
• Graduated cylinder or small volume measuring cup magnesium to the media. These added nutrients may prove beneficial
to the crop and are seldom harmful. Potassium bicarbonate injects
• Plastic saucers easily, leaves no residue, but offers a shorter-term solution compared
to flowable limestone. Large amounts of potassium are applied as
• Plastic sample cups a result of this treatment, and higher rates can distort the foliage of
some plants. Leaching with a balanced feed at the next irrigation helps
• pH and EC meter(s) to overcome the imbalance. Flowable calcium carbonate, available
as CalOx, is easier on injectors than flowable limestone. However,
• Crop to be tested in low flow-rate drip systems, the CalOx may be deposited on the
inside of irrigation pipes; hand watering is preferred in this scenario.
Test Procedure In addition to pH adjustment, CalOx does provide calcium to the soil.
1. Irrigate crop (or sample pots only) to saturation following normal Specific grower needs guide the decision regarding which of the three
products to use. When utilizing re-circulated water, flood irrigation,
irrigation practices, i.e., use fertilizer if using a constant feed low-volume drippers prone to clogging, or when visible residue would
program. be a problem, treatment with potassium bicarbonate is the preferred
choice. When producing longer-term crops, flowable limestone or
2. Select five representative (random) pots from the crop for sampling. flowable calcium carbonate are preferred. Regardless of the product
used, the following points should be kept in mind for flowable
3. Allow pots to drain for 30-60 minutes (be consistent across limestone, flowable calcium carbonate and potassium bicarbonate:
sampling events).
• Most of the pH change will occur within 24 hours of treatment, with
4. Rinse plastic saucers with distilled water, shake excess water from a slight increase occurring in the next 7 days.
saucers.
• Media pH should be re-tested seven days after treatment; reapply
5. Place saucers under pots, one pot or cell pack per saucer. treatment as necessary desired pH is reached.

6. Add distilled water to the container in sufficient volume to collect 1.7 • All three products should be applied to leach for maximum pH rise.
oz (50 mL) leachate from the pot. Trial and error will help to identify
the best volume for your mix. Expect to add increasing volumes • Avoid applying these products to dry media.
of distilled water for larger pot sizes. A good starting point for 6.5"
azalea pots is 100 mL of distilled water. Keep in mind that leachate • Foliage should always be rinsed prior to any residue drying on the
volumes above 60 mL will be too dilute to provide reliable data. leaf surface.

7. Use meters to test pH and EC of the leachate from each pot. • Always flush injectors following treatment.

8. Average the results from all five containers. Top dressing of pelletized or granular limestone products is generally
not an effective method of increasing media pH in a timely manner.
9. Rinse all containers and saucers thoroughly before storing or This can bring less predictable results, and involves more complicated
processing the next sample. application rates. Special cases may warrant top dressing; the
GGSPro team can help evaluate this need.
Rapid Corrective Measures for Media pH
On occasion, media test results will reveal an extreme problem with Application Instructions: Use the recommendations in the table
media pH that requires immediate correction. It is critical to crop health below to achieve the desired change in media pH. Note that actual
and salability to correct the pH as quickly as possible. The following media pH changes can be difficult to predict because pH is a
methods to achieve the correction are proven safe and effective. logarithmic scale.

Raising Media pH in a Production Environment
When media pH falls below the desired range, swift, effective correction
is desired to avoid crop problems. Fortunately, three inexpensive
products are readily available and appropriate for both greenhouse
and nursery media: flowable limestone, flowable calcium carbonate

Desired Change*

Product Application Method Low Change Fertilizer B
Limestone-F (-0.5 point change) (-1 point change)
Injector - 1:100 Direct inject1, one application Direct inject1, two applications
Potassium bicarbonate Hozon - 1:15 0.75 gal plus 2.5 gal water 1.5 gal plus 2.5 gal water
CalOx Bulk Tank2 1 part to 100 parts water 1 part to 50 parts water
Injector - 1:100 1 lb in 1 gal water 2 lb in 1 gal water
Hozon - 1:15 12 oz in 5 gal 24 oz in 5 gal water
Injector - 1:50 or 1:100 Direct inject1 at 1:100 Direct inject1 at 1:50

1Do not dilute the stock solution prior to injection
2To avoid potential damage to injectors, pump flowable limestone out of a bulk tank.

20 Griffin Gazette Spring 2016