An introduction to injection molded propagation trays

There are lots of different options when considering vegetable propagation trays – size, cell dimensions, material, color and so on. Here, we go through some of the key areas to think about when deciding on a tray and address some concerns with injection molded containers.

When deciding on the tray, it is important to look at your current greenhouse or nursery set up to get the right outer size of tray. Plants per square foot is the important factor, rather than purely how many cells the tray has. A 144 cell tray will perform very differently to a 128 cell 26x13” tray, for example.

Injection molded trays represent the best return on investment over the life of the tray. If you are constantly having to throw away your trays after a year or two because they break, or you can’t clean them well enough, a tough plastic tray will be the right option for you.

Below, we address some of the more common concerns people have with making the switch from Styrofoam or thermoformed trays.

It’s a feature we don’t see all that often – so what are root training ribs and why are they important for vegetables?

Only some vegetable trays contain this feature. Having these ribs means that roots grow down and are forced to the drainage hole, rather than circling and choking up. It’s a simple thing that really improves plant quality – you get the roots right and the bits above the soil have a good chance of being great too. These great roots also mean that the plant pulls very easily too, meaning less time wasted trying to tease seedlings out and fewer broken trays.

Some trays claim to increase the number of plants per tray over Styrofoam equivalents – does this not reduce plant quality?

The right injection molded vegetable trays do not require a large outer rim. That means that it is possible to fit in more cells per tray. Styrofoam trays have large outer rims and thick cell walls due to the nature of the material that they are made from, while thermoformed trays require the rim to stop them from bending and to add rigidity.

Injection molded trays trays do not require a rim so can be produced with more cells per tray, but can also space them out enough to ensure that plant quality is not compromised. Therefore, you will be able to produce more cells per tray, which means more plants per greenhouse and more profit for you!

Injection molded trays are much more expensive than throw-away trays like Styrofoam or thinner plastic models – how quickly, if at all, can growers make their money back from such a big purchase?

Injection molded trays are tougher, heavier and have more plastic in them - so they are a bit more expensive. In terms of getting money back, that’s quite a complex answer as it depends on crops, size of nursery and how many seedings you do a year. However, Proptek has found that growers’ ROI can sometimes even be less than a year – but we typically say 2-5 years to be on the safe side. This extra money comes from 3 places: not having to buy any trays in subsequent years, more plants surviving to be sold (even more so if you have a tray that increases cells per tray, as above!), and that the trays are easier to work with. It takes less people less time to fill, seed, move and then pull the plants from the trays, helping cut down labor costs. We have some great spreadsheets we can tailor to individual set ups that we can show if people want to get in touch.

Isn’t re-using the same tray year after year dangerous in terms of disease carry-over?

If done incorrectly, yes – very much so. Thermoformed trays and styrofoam trays are very hard to clean effectively, and the risk is much higher, whereas injection molded trays are much easier to sterilize. This cleaning can be done safely and at a low cost too, using only water and steam. No nasty chemicals are required, which helps keep future plants safe, as well as being nicer for the people handling the trays and also the environment too. More information can be found here.

What are the environmental impacts of an injection molded tray? Is using plastic really a good thing?

It is! Check that your supplier is making their trays from reprocessed material – then once the tray is worn out, it can often be reprocessed yet again. It is plastic – but when you look at the awful waste (and expense!) that something like throwing away Styrofoam produces, it is much, much better.

Injection molded trays are much easier to clean – they just need a quick tap and then a steam for a couple of hours. This sterilizes them with no nasty – and pricey – chemicals. As the trays are tough, this heat and steam doesn’t damage them like with Styrofoam or thermoformed trays.