In the past few years, I’ve seen more and more growers across the globe adding LED grow lights to HPS to increase light levels and yields for their gerbera daisies. Unlike high pressure sodium (HPS) lighting, higher light levels can be applied with LEDs because they produce very little radiant heat and use less electricity. 

This enables growers to achieve the perfect balance between warmth and light with LEDs, so that they can produce more crops and potentially accelerate the payback on their LED investments.

Setup of floriculture trial
These benefits prompted us to conduct a floriculture trial in our climate-controlled test facility at BrightBox in Venlo. Most of the requests that we receive are from growers of young plants, so we ran a trial on the propagation phase of flowers. We chose a wide range of annual and perennial plants, including Begonias, Petunias, Calibrachoas, Dianthus, Gerberas, Celosias, Alternatheras and Impatiens.

For this trial, we translated the cultivation conditions of a greenhouse to a climate-controlled environment and added the experience of our colleagues, City Farm plant specialists. Light levels were chosen based on the reference greenhouse environment with daylight, as well as scientific literature and the experience of growers. The light spectra used in the test were aligned with a number of growers to meet their quality standards for the different varieties of flowers. Growth speed is one requirement from growers, but good plant quality is the first priority. In this case, a plant is considered good if it has a compact shape, enough leaves and branches and a good root system. In addition, a good plant should be able to quickly establish roots and bloom as it moves to its next growth phases.

By drawing upon our experiences and the scientific literature we were able to extract enough insights to develop light recipes that would produce these plant characteristics. For example, many plants react to a higher amount of blue light by becoming more compact. The length of the internodes becomes shorter. Some plants benefit from far red light by germinating faster and developing stronger roots, while other react by bolting and drooping. 

Results from floriculture trial
Our results showed that, as expected, each variety of flower reacts differently to a light recipe. The climate settings are also important in this respect. Higher temperatures resulted in faster, but less compact and less robust, growth. The results confirmed that growing floriculture young plants in a daylight-free environment is possible and all about finding the right balance between climate factors and lighting. In fact, the choice of light intensity and light spectrum plays an even greater role in a vertical farm than in a greenhouse.

This is just a first screening, but the trial gave us clear insight into the possibilities of cultivating diverse varieties of young annuals and perennials in a daylight-free environment. As with all trials, there were also plants that did not fare well as a result of a certain light recipe. But we learned from these results as well. The majority of the light recipes tested produced good results in terms of compact, robust plants with a good root system. There is plenty of room for optimisation, depending on the most desirable characteristic for a specific variety. We also saw that it is definitely possible to cultivate good quality plants for several crops under one light recipe. 

Even though chrysanthemums are one of the most popular cut flowers, the use of LED grow lights for their cultivation in greenhouses has been limited. Philips has done much research on these plants over the years, but had not been able to test the perfect light spectrum on a large scale until recently, so it was hard to justify the investment to growers. Recent research results, however, may change growers' minds on this subject.