7/2/2013 - By Dr. Raymond Snyder

Potted annuals and perennial are often unintentionally subjected to water stress conditions prior to and following incorporation into the landscape.  Water stress is not solely the result of a deficiency of applied water through irrigation or hand watering.  The hydrophobic nature of potting mix media can further promote undesired water stress on potted plants.  Furthermore, highly porous potting mixes can lead to preferential water flow within the root-zone resulting in poor water distribution throughout the potting mix.

The use of granular wetting agents may help to reduce water stress associated with hydrophobic potting media and poor water distribution throughout the root-zone.  Granular wetting agents are designed to reduce water repellency and improve water distribution when incorporated into root-zone media though the use of a light-weight, hydrophilic carrier infused with a liquid wetting agent component.  As a dry solid material, granular wetting agents can then be incorporated into potting media mixes so as to increase the efficiency of applied water.

Recently Harrell’s conducted a long-term experiment to determine the ideal granular wetting agent product for use in potting mix media.  The goal was to identify a granular wetting agent that would significantly improve root-zone water relations and reduce potted plant water stress over a period of 120 days.

In this study, granular wetting agents were added to one-cubic foot increments of potting media at 1 and 2 pounds per cubic yard.  The mixed potting media was then added to one gallon pots to which bush daisy liners were placed in each pot.  The pots were placed on ground cloth in an irrigated, outdoor nursery environment.
Approximately 120 days later, after plants reached maturity, irrigation was withheld for several days to induce wilt.  A total of four wilting cycles were conducted to examine the effect of the granular wetting agent products on wilt.  Finally, two weeks following the last wilting cycle with no irrigation, the bush daisies were cut at ground level in the pot and discarded in order to examine the ability of the granular wetting agents to distribute applied moisture uniformly throughout the potting mix media.

In this study it was determined that the inclusion of a granular wetting agent significantly increased the time to wilt and improved moisture distribution throughout the potting mix media without negatively impacting infiltration rate.  Furthermore, Harrell’s Brilliance G was identified as the optimal granular wetting agent when applied at 1 pound per cubic foot of potting mix media.  The inclusion of Harrell’s Brilliance G in this study improved plant appearance, reduced wilting, and improved moisture distribution in the root-zone relative to the control for up to 120 days after application.  

Infiltration ratings, moisture measurements, and moisture distribution ratings following application of 3 cm water to air-dried soil in pots.

Means for percent of pots without wilting, by Rate, using observation dates as replications.

Visual ratings of plant growth and health. Study initiated February 16, 2012

Special thanks to Brad Smith and Dave Edison from Harrell’s and our Partners at Mulvehill Nursery for their help with this study.