Is your propagation mix holding too much water?

If your growing media stays wet too long, this can delay rooting and create an ideal environment for root diseases. Possible causes and solutions:

Check if the mix has a high water holding capacity

  • Fill propagation trays with your current growing mix, and with other propagation mixes for comparison. Weigh the trays after irrigating and draining – most of the weight will be from water unless you are using a heavy component such as sand.
  • You can root plants in a tray with different mixes, fully irrigate, and let the mixes dry until plants wilt. Count the days for plants to wilt. A mix with more plant available water will take longer until plants wilt. Refer to our Plant available water test in BackPocketGrower.com (BPG) for detailed instructions.
  • Test air and water porosity following our Porosity testing (air and water) protocol in BPG. A “wet” mix will have lower air porosity and high water porosity.

Over hydrated plant

Are particles too fine?

The finer the particles, the smaller the pores, and the wetter the mix.

  • We have a protocol to run air-dried media through a stack of screens, with guidelines for plug and liner propagation substrates (see our Testing particle sizes protocol in BPG).
  • If your mix is too fine, consider a different source of the same components with coarser particles. That will increase air porosity and decrease water holding capacity.

Hand demonstrating testing particle sizes

Are you over-compacting the mix?

  • Compacted growing mix holds less air, and more of the container volume is taken up with solid and water.
  • For loose-filled trays, check there is a small amount of settling after irrigation. See our Settling and compaction in loose filled trays protocol in BPG. Adjust brushes in tray-filling equipment.
  • For paper-wrapped pots, such as Ellepots, compaction can be measured using a digital force gauge by pushing a 1-inch (2.5cm) disc down 3/8-in (1 cm) from the top of a wetted pot (see Measuring compaction in paper wrapped pots in BPG). Reduce the vacuum setting to decrease compaction.

Testing the compaction of the soil

Are you using the right tray?

  • Using a vented tray helps drying.
  • If you jam Ellepots into the wrong tray there is less air circulation around the paper and slower drying.

Hand showing off tray

Are you over-applying the water?

  • If you over-irrigate, the mix will stay wet and dry slowly. Over-watering leads to more water leaching out the drain holes. Place a collection tray under your trays to measure leaching – the goal is to minimize leaching while keeping media at a target moisture level for rooting.
  • How are you making irrigation decisions?
    1. Use the 1 to 5 moisture scale for plug trays in BPG to improve decisions on when to water, such as letting rooted plants dry to Level 2 or Level 3 before irrigation.
    2. Do not irrigate just based on a time clock. Use light or VPD (vapor pressure deficit) setpoints.
    3. Irrigate plants based on crop stages. Crops need more water for callus, less for rooting, and wet/dry cycles for finishing.

Tray with mix

Tray with mix

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.