Strawberries have quickly become superstar crops in the controlled environment agriculture (CEA) industry, captivating growers and consumers alike. While more and more growers venture into soft fruits — strawberries, in particular — there’s still much to be learned about cultivating this crop in controlled growing environments.
One area of research has involved LED lighting and the impact of far-red light in CEA strawberry cultivation. It’s long been understood that far-red light can impact plant shape dramatically. Lettuces, for example, grow wider and have larger leaves with far-red in the lighting mix. But most other plants respond with increased stem elongation, which has pros and cons depending on the degree of elongation and the crop involved. Strawberries are one such crop.
Since 2019, lighting leader and Philips parent company Signify has been conducting research into the effects of far-red light on June-bearing strawberries using Philips GreenPower LED lighting. Signify plant specialist Peer Hermans specializes in soft fruit, lettuce and young plants. The task falls to him to translate Signify’s research into practical advice — cultivation recipes — for growers.
Early Signify research confirmed that far-red affected strawberry plants in significant ways. But there was no indication that far-red light resulted in increased fruit production, as growers might hope. As a result, Hermans notes, the value of far-red lighting for strawberry growers was difficult to quantify.
One challenge facing researchers was the combination of plant data, variety and cultivation site. New research was needed to answer the question: What role can far-red light play in the cultivation of June bearers?
Far-red light and strawberry trial parameters
To establish what added value far-red light holds for CEA strawberries, Signify conducted a research trial with Botany Group. The study focused on two strawberry varieties that are favorites for winter production under artificial lighting: ‘Sonsation’ and ‘Sonata’. The varieties were planted alternately in six rows, with increasing levels of far-red light from 1% to 9%. “This enabled us to accurately test the various parameters: What is the effect on plant development, fruit appearance, and production?” Hermans says.
Another important factor in this study was the choice of planting date. “We opted for mid-October to optimally measure the impact of lighting with far-red. This is because mid to late October is the most challenging time to start a winter crop, as there is very little natural light both during the vegetative stage and during harvesting and the effect of the spectrum is therefore at its greatest,” Hermans adds.
The strawberry plants were given a total light intensity of 195 micromole/s/m2 including far-red. The maximum lighting period was 16 hours per day, and the total number of lighting hours was approximately 1800.
Microclimate benefits with stem elongation
Following the research trial, the original conclusion regarding increased production remained unchanged. Yes, far-red light spurred an increase in total biomass (stem and leave mass, both dry and fresh weight). But adding far-red to the lighting did not translate into increased fruit production in kg/m2. But those were not the only results.
Other potential benefits were observed, particularly in terms of stem elongation. “We know from experience that certain varieties grown under full LED tend to remain on the compact side, which — when combined with other climate factors — can create a poor microclimate around the plant,” Hermans shares. “This can lead to a less-active crop, too much moisture around the fruits and excessive root pressure, which can negatively impact fruit and crop quality.”
In contrast, exposure to far-red light encourages elongation of leaf stalks and truss stems in June bearers, which reduces the risk of these problems occurring. For growers, this creates greater flexibility in cultivation and allows greater scope for climate control. “This effect was stronger in ‘Sonsation’, which already has a tendency towards stem elongation, than in ‘Sonata’,” says Hermans.
This indicates the choice of variety coupled with far-red light plays an important role, especially regarding improved picking performance and related labor benefits. The improved microclimate observed with stem elongation could lead to a reduction in the use of chemicals as well.
Far-red as a cultivation ‘safety net’
Hermans shares that there’s no one-size-fits-all solution, so decisions regarding use of far-red light may be tricky for growers. “After all, the most energy-efficient option is to leave it out completely,” he says. However, benefits of stem elongation in June-bearing strawberries may warrant adding 5-6% far-red as a “safety net” to improve the microclimate around the plant, minimizing the risks outlined above. That’s one reason Signify has offered the option of a certain percentage of far-red for June bearers in its standard recipes for some years.
“Developments around full LED are moving at breakneck speed, and we constantly keep our finger on the pulse in relation to strawberry,” Hermans says. “One recent development, for example, is the dynamic light module. The first color-adjustable products are now available, enabling growers to make different choices and opt for greater flexibility without necessarily using more energy.” What does this mean for the grower? Ongoing Signify research promises to reveal answers in the coming years.
Images courtesy of Signify