Hygiene & Tray Cleaning

Tray hygiene can be a major problem which sometimes means growers have to use a new tray for each successive crop. With Proptek’s range of long life injection molded plastic trays this does not need to be the case.

There are high pressure tray washers being produced specifically for injection molded plastic trays which would destroy Styrofoam or flimsy blow-molded trays. These high pressure cleaners effectively remove not only the dirt but even cells with complete root balls still in them.

If an injection molded tray is clean i.e. the dirt is removed from its surface then it is almost as good as sterilized as the disease is on the dirt and not the tray. This is not possible in practice with thermoformed or Styrofoam trays.

Heat Sterilization.

A lot of nurseries have used heat via steam from a boiler at about 75C ( 170F ) to destroy all disease on or in the tray. This is most commonly done with trays stacked in a confined space such as a shipping container body to raise the temperature to the required level. Steam is good as it penetrates well and has no potential chemical residue problems. However, care should be taken not to exceed the target temperature and a good thermostat should be used.

Tips for setting up your steam-room container:

1. First you need a method of creating steam at 170 degrees Fahrenheit.

2. It is very important to have a backup system that cuts off the steam if the temperature get to 180 degrees.  With the best will in the world, valves can jam and machines can fail. If left unchecked, this could mean complete loads of trays/containers shrinking, warping or melting.

3. The time to get to your temperature of 170 degrees will vary depending on whether it is winter or summer or the first, second or third load of the day and therefore it is important to start the timing from when the container reaches the temperature and not when you turn it on. We recommend that containers stay at the correct temperature for 1 hour or more after it has reached 170 degrees Fahrenheit.

4. If possible, invest in a decent system that allows for full automatic temperature control and timings with built-in emergency stop. All you have to do is push the button to start the process and then leave it and it will turn off after the prescribed amount of time at temperature.

5. Opening the doors as soon after the time is up as possible is advised, as moisture escapes better as the product cools down and the product ends up dryer – important if it is going straight into a new production cycle as wet product means soil will stick to it etc.

6. A very Important last point! Please make sure the container is not airtight as it may explode!  Lots of leaks with steam coming out is no bad thing.

If you would like more details on steam generation, Sioux have a lot of details that could prove useful: https://sioux.com/steam-generators 

Other Methods

There are other methods that you will see to clean trays. These work perfectly well, but have their downsides. We highly recommend using the heat/steam method in most cases.

  • Chemically. This works very well with our trays as the chemical will not penetrate the material and as the trays stack with a small gap the chemical will drain out or evaporate easily. Liquid chemical dips or even gassing with methyl bromide are possible here.
  • Washing. As stated above many people now rely on a good tray washer to remove the dirt and therefore almost all of the disease. Some tray washers have a small section at the end where a chemical can be misted onto the clean tray to be 100% sure.

Please do not hesitate to contact us for more details or advice for your specific tray or set up.