Image source: OSRAM

So, the Papillon LED test bed is now in full swing!! Growing out successive crops over a tiered growing system gives a fantastic opportunity to identify differences in growth between different crop types, different lighting technologies and most excitingly, different spectrums of light. So, what exactly have we got going on here and sort of information are we expecting to see? We thought it would be best to break down what exactly is happening, and what we are looking for.

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The Set-Up

An industrial metal shelving unit has made the perfect basis for a three-tiered racking system. Each layer has been positioned in such a way that the overall PAR readings from each light source, are as even as we could get them across the entire growing area.

Having made use of a hand-held PAR meter and a grid-based sample system, the best position for each light was calculated after a fairly long process of trial and error.

Red, White or Blue?

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Appropriate spectrums for plant growth is indeed quite a hot topic. Not just with the recent leaps made in LED technology, but growers worldwide have constantly wondered what spectrum will give most beneficial growth. Does the blue of a metal halide give different growth to that of the orange HPS?

The aim here is to get an insight into exactly this principle in a bit more detail. Each layer of the tiered racking system has a different spectrum of light but set to the same intensity of PAR levels at crop level. Morphological differences have often been noted from growers using lights of different spectrums, so this is exactly what we are delving into!

Players of the Game

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A few different types of plants have been selected for the first run. Lettuce, Basil, Dwarf Marigolds and Radish have been selected to try and get a quick insight into how the different lights effect different varieties of plants. The lettuce will give a good idea of how fast growing leafy type plants grow. Basil will indicate how short statured herb type plants will perform. Dwarf Marigold should show any impacts of the lights on quick flowering plants and the radish will give an example of how bulbing plants will perform.

Now of course we are expecting differences in growth, but particularly with the first cycle of plants under the lights, that may well happen anyway! Varying conditions over the three levels might impact growth so it is the perfect opportunity to nail down any differences in conditions between the levels. There is always something that needs tweaking in a grow room! For example, the lower level shelf was reading roughly 3-4°C lower in temperature than the top two shelves. Using a thermostatically controlled heat means that you have control over un-ruly root zone conditions.

Ready, set, Grow!

So, with everything ticking along nicely, the plants were split up promptly after germination, and planted out under each respective light. After only a short time from germinating, they were ready for replanting into slightly larger pots. A high quality organic potting compost was used for each crop type on the basis that each plant will have access to the same high level of organic nutrition throughout it’s life. With such healthy root systems developed in their initial cell trays, they were at a great point for transplanting.

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Of course, before and after this point they were gently hardened-off. For those of you unfamiliar with this phrase, it simply means getting plants used to a different environment. In a propagator, as a seedling, plants like it very humid. As they get larger and older, you do not want such a high humidity as it increases the chances for moulds and diseases to take over. So, you need to slowly drop the humidity to gradually prepare them for the outside world. There are many methods, but simply opening the propagator vents in stages will get things started in the right direction. Check out the blog All about Hardening off, for the finer details!

Let it Grow

So, at this point it is more-or-less a case of letting the plants grow and recording the differences! Obviously, there is things like watering and adjusting for any environmental changes that need to be done, but the plants now do most of the hard work. Without trying to tease too much, differences between the lights, seemed to rear their heads within the first few weeks of growth!