Head Grower, Tomatoes, Gourmet Mokai

At last weeks open day at Gourmet Mokai, head tomato grower Hans van Veen presentation focused on the hurdles he has had to overcome growing tomatoes using supplementary LED’ lighting.  The presentation was an insight to how the ‘mind set’ of the grower has to change and how he has had to acquire new techniques and skills to maximise the potential of using LED’s. LED lighting has been installed at Gourmet Mokai site to improve winter production and provide continuity of supply to the market.

Growing Techniques Hans has had to adjust to:

• Irrigation:  Irrigation is normally triggered via the collection of accumulated light sum from the outside weather station, (or solar trigger) so there has been a need to change to irrigate on slab water content setpoints.  As the lights are turned on at midnight in the middle of winter you need to irrigate like you would during a normal day.  It is difficult to calculate the accumulated light sum, so a new technique is being used.  The approach has been to install Grodan Grosens and have them integrated with the environmental computer.  Hans now has the option to irrigate on water content targets he wants to achieve.  The plants are almost determining its own need for refreshment!  Irrigation from weigh scales could also be a possibility if set up correctly, and for growers in coir substrates it would be an alternative option.  You could irrigate on time but it is not accurate enough. The LED’s are generally on most days depending on the strength of the outside light levels, which again makes irrigation of solar trigger to inaccurate.

• Turning the LED's on and off:  The two installations of top lighting and inter-lighting have different strength micro-mol.  The top light has 125 µmol/m²/s and the inter-light 75 µmol/m²/s.  Each installation will turn off at different outside calculated light intensities.  The top light will turn off at 350 watts and the inter-light at 450 watts.  Currently the lights are set to be available for 16 hours a day.  It is anticipated they could be used for up to 18 hours day for tomatoes.

• Vegetative-Generative Balance: When you look at the stems you can see that the plants have at times been too strong, it has been a challenge to keep the plants generative.   Truss quality is affected if plants are not kept in balance.  Having more light has increased the vigour of the plants, so it is very important to keep focused on burning the extra plant energy and putting it either into the fruit or increased growth.  Stem density is a factor and understanding the best planting density with the amount of light achievable is important.

• Labour:  Hans noted that during the winter period it is generally a time the staff worked ‘under less pressure’ but with the LED’s staff have had to get used to working in summer conditions all year round.

• Insects: Under LED’s the bumble bees will not navigate sufficiently, so automatic bee hive openers/shutters are used, so that when the LED’s are switched on late at night the bees cannot leave the hives until the natural light comes in the morning. White fly is hard to manage as the extra temperature allows them to breed as they would in a normal summer, therefore more control options are required. 

• Disease:Small amounts of leaf mould has been detected and botrytis especially by the door where the temperature can fluctuate.

• Heating pipes: With LED inter-lighting (giving small amount of heat/radiation) and the minimum grow pipe temperature high, to keep the fruit and the leaf area warm, the pipe rail heating system on the ground was turned off, however this created a health and safety issue as the pipes condensate and became slippery, a minimum pipe was re-introduced on the pipe rail.

• Temperature on Dark Days: Giving more heat input on a dark day is still something Hans is trying to adjust to. 

It has been a fast learning curve, Hans said "there is still an awful lot to learn”.  So far, he gives the LED’s the big thumbs up and is very positive about them.  I am sure we will here more about them in the future. 

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Article Written by Stefan Vogrincic, Consultant, Grower2Grower