Is your growing substrate hard to rewet?

If water is not quickly absorbed into your growing substrate, it will lead to waste of water and fertilizer, excess fertilizer run off, and wilting plants.  Possible causes and solutions:

Have you tested wettability?

  • Examine trays and cells: after flat filling or during crop production, irrigate the tray as normal and check to see if the mix is evenly wet.
  • Refer to our Substrate wettability tests in (BPG) for detailed instructions.
  • A droplet test (absorption of a droplet of water applied to the surface of the substrate) can be used to test wettability after flat filling or re-wetting after the mix dries down.
  • A float test (placing the substrate in a cup of water) can be used to test wettability for both loose and paper-wrapped pots.

Rewetting tray

Is the wetting agent working well enough?

  • Wetting agent needs to be uniformly mixed with the growing media.
  • Granular wetting agent is easy to apply but it takes time to react with media particles. Liquid wetting agent provides uniform wetting and rewetting.
  • Increasing the concentration of wetting agent, or applying extra wetting agent in a watering tunnel to the growing crop may improve wettability and re-wettability.
  • However, make sure to trial first and check plant growth and rooting, because wetting agents can be phytotoxic at high rates.

Testing if the wetting agent works well enough

Is the growing mix delivered too dry?

Dry mixes are harder to rewet if they contain hydrophobic components such as peat. Increasing initial moisture level (up to 55% moisture) will improve wettability.

Testing if the growing mix was delivered too dry

Should you change components?

Some peat sources tend to be harder to wet than other peat sources. Components such as coconut fiber are not hydrophobic).

Are fungus or mold growing on the surface of growing media? 

Once mold or fungus dries on the soil surface, it can form a hydrophobic layer that is hard to rewet. 

Mold growing on the surface of growing media

For more information: Contact authors Jinsheng Huang and Paul Fisher of University of Florida IFAS Extension, and Dr. Bill Argo of Blackmore Co. Thanks to our Floriculture Research Alliance at University of Florida sponsors including A.M.A. Plastics, Blackmore Co., Everris, Fine Americas, Greencare Fertilizers, Klasmann-Deilmann, Pindstrup, Premier Tech Horticulture, Quality Analytical Laboratories, Sun Gro Horticulture, and leading young plant growers. The University of Florida does not endorse any product, and our research focuses on quality testing on these and competing products to assist grower success. June 30 2015.