Plastic Seed Trays vs Polystyrene Seed Trays

Plastic Seed Trays are made of durable injection moulded plastic.

Using plastic propagation trays provides a great many benefits for growers and can directly help your bottom line and return on investment.

1. Super Long Life Design

Typically, a Polystyrene tray will only last about 4 seasons. Good quality injection moulded plastic trays are able to last for over 10 years on average – and as long as 20 years if care is taken. While the capital outlay to acquire plastic trays is generally larger than the capital outlay to acquire Polystyrene seed trays, over the course of ten years they are far more economical in purely cash terms. Plastic seed trays also offer the added benefit of better plants, better sterilisation and more plants per square foot, plastic trays become not only financially viable but financially beneficial.

With a Polystyrene tray, the first damage is typically a broken outer wall where a cell has snapped out. This means that the next time you fill this tray the soil, and possibly the seed, falls out. This can get very expensive very quickly as seeds can often be quite a large investment themselves. Eventually, it comes to a point that you are losing too much money from broken cells, so you simply through the tray away. Injection moulded plastic trays do not present the same challenges.

2. Improved Sterilization and Disease Reduction

To sterilise injection moulded trays or containers all that needs to be done is a simple surface sterilisation. Plastic trays will not deform at the high temperatures required to clean and kill the disease. Deformed trays could influence plant pulling and cause seedlings to be damaged. To sterilise Polystyrene you have to sterilise the whole block of material and this is only practically possible with heat. When using polystyrene trays, you run the risk of losing some trays after a single sterilisation, but certainly, after a couple years a good proportion of trays will become unusable.
Over time a Polystyrene tray will allow roots and disease into the Polystyrene and thus you get a tray to tray variation and diseases carry over, this never happens with an injection moulded tray.

3. Improved Plant Quality & Air Pruning

Moulded plastic trays offer a higher level of detail in the form of plastic ribs and holes. This facilitates exceptional and natural root structures as the seedlings grow. Roots that are not tangled up in themselves grow a lot better, resulting in a stronger, much more consistent plant.

Polystyrene trays are porous, this might cause water and fertiliser to get lost. Eventually, roots also penetrate polystyrene trays, this causes roots to break off during the pulling process. In general plastic moulded trays result in a better quality, more uniform plant but they also pull a lot easier.

4. Better Integration with Mechanization

As plastic is a more precise material than Polystyrene, injection moulded trays better suit automatic transplanting systems. Plastic moulded trays are more durable too. They survive many more seedings and extractions.

5. More Plants per Square Foot

As plastic is tougher and stronger than Polystyrene, cell walls can much thinner and trays no longer need a thick outer rim to keep the tray rigid. The thinner rims mean that more cells can be placed into the same space without affecting the spacing of the plants too much.

6. Increased Cell Volume

Rather than increasing the number of cells, injection moulded trays can also be designed to have a larger cell volume. The greater cell volume is achieved because of the tough nature of plastic. The strength of the material allows the cells to share thin cells walls, thereby increasing cell size when it’s required, such as when you require more soil and the water and nutrients it carries.

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