Are my paper-wrapped pots too compact?

Over-compacted cells reduces the air porosity in the growing substrate, which slows down rooting. Compaction also reduces the number of trays produced per bag of mix, thereby increasing production cost. The following pointers are useful if you are making paper-wrapped pots such as EllepotsTM.

How can I measure compaction?

  1. With your finger, you can press down on the mix in the pot, and with experience get a feel for the amount of compaction. The pot should be easily compressed when it is moist.
  2. You can also objectively measure compaction of individual pots with a digital force gauge. Push a 1-inch (2.5-cm) diameter disc down 3/8-in (1 cm) from the top of a well-irrigated pot (see our Measuring compaction in paper wrapped pots testing method under the 'Root substrates' training module of this website). If the compaction reading on the meter is more than 1500 grams, then the pots are over-compacted.

Force meter pressing on paper pot

Vacuum setting on the machine

The vacuum setting in an EllepotTM machine affects how tightly the substrate is compacted inside the paper tube. Increasing the suction power will increase compaction of the pots. The vacuum should never need to be above 0.2 – if such a high setting is needed to hold the pot together, the peat is probably too fine, the mix is too dry, or the pot is being cut too short (shorter than the diameter is wide).

Vacuum dial at -0.3

Moisture level when making paper-wrapped pots

  1. If the substrate is too dry, it normally leads to under-compaction. Under-compaction will cause ripping of paper during the cutting process, and lead to incompletely-filled pots.  Growing mix will fall out of the bottom of the pot. Dry pots are also hard to rewet in propagation.
  2. If the substrate is very wet, it will be more compacted during pot production. You can check the substrate moisture level by weighing the bags of substrate (where heavier equals wetter) or test by hand.  For paper-wrapped pots, a target moisture level is 60 to 70% of total weight.  At this moisture level, the peat based substrate will have a light brown to tan color; it will form a weak ball in your hand and will break with a bounce. See our Look and feel method (in the 'Irrigation' training module of this website) for guidelines on how to test moisture.
  3. If the substrate moisture level exceeds 70%, do not use this substrate without drying or blending with a drier batch, because it will clog the machine and will produce a lower number of trays per bag of substrate.
  4. If the growing medium is too dry (below 60%, add water before making the pots.  When adding water, preferably spray onto the substrate on a mixing line, or if necessary in the hopper itself.  Use a spray nozzle rather than a coarse hose.  Mix in water as evenly as possible, but without damaging the particles.

Hand demonstrating the look and feel method

Packing, storage and shipping

Make sure to place a cardboard or similar barrier between each layer of trays, or offset them so that upper trays are not pressing down and compacting substrate below.


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.