Test settling and compaction

Goal: To consistently fill propagation trays evenly, while avoiding excess settling or compaction.

Why is it important?

Tray filling practices affect how much solid, air, and water are in each cell. Excess settling reduces the cell volume available for root growth. Excess compaction reduces air porosity which can limit root growth. Uneven filling across the tray results in uneven drying and plant size.

How do you measure it?

Step 1. Requirements

Requirements

You will need: A ruler, plug or liner tray, and propagation substrate

Step 2. Fill propagation trays

Fill propagation trays

Each time the substrate type and tray size is changed, fill 3 trays with the adjusted flat filling equipment. The dibble may be used, but do not sow seeds or cuttings, and do not cover with vermiculite.

Step 3. Irrigate to container capacity

Irrigate to container capacity

Bring the substrate to container capacity by passing through a water tunnel for 3 to 4 times, through a subirrigation conveyor, or by using a fine mist nozzle with hand irrigation.

Step 4. Measure settling

Measure settling

After the tray drains for 30 seconds, drop the irrigated tray onto a table from an 8-in (20-cm) height twice. Measure the settling (loss in surface height). This can be done with a ruler by measuring from the plastic tray ridge down to the substrate surface, or quickly estimated by eye.

How do you interpret the measurements?

Underfilled:

  • Substrate surface drops 10% or more from the ridge of the tray (which is 5 mm in a 5-cm tall 128-plug tray).
  • Increase flow of substrate from the hopper to the tray.

Unevenly filled:

  • Variation of more than 5% (3 mm in a 5-cm-tall 128-count tray) between the lowest and highest cell in the tray.
  • Check adequate and even flow of substrate from hopper, adjust brushes.

Ideal:

  • A small amount of settling occurs (less than 10%, 1 to 4 mm in a 128-count tray), enough to provide a slight reservoir for irrigation, and keep plant roots within each cell.

Overfilled:

  • Ridges of the tray are covered with substrate, or little/no settling occurs.
  • Reduce amount of substrate delivered to tray, and compaction into the tray.

For more information: Contact authors Jinsheng Huang and Paul Fisher of University of Florida IFAS Extension. Thanks to our Floriculture Research Alliance at University of Florida sponsors including A.M.A. Plastics, Blackmore Co., Everris, Fafard et Frères Ltd (Canada), Fine Americas, Greencare Fertilizers, Pindstrup, Premier Tech Horticulture, Quality Analytical Laboratories, Sun Gro Horticulture, and leading young plant growers. August 23 2014.