Grow Flavourful Basil with LED Grow Lights

Basil is a popular herb in a variety of different cuisines worldwide making it a popular growing staple when it comes to home gardeners. Its avid culinary use is mainly due to its unique flavour and aroma, however, growing basil under different lighting conditions can affect not only its growth but its taste and aroma too. 

Today, Basil is increasingly commercially grown indoors under LED grow lighting, and home indoor gardeners are also starting to accomplish the same feat. But what are the best lighting conditions to generate the optimal Basil crop indoors? To help answer this question, we have already defined optimal light intensities (PPFD) and light quantities (DLI) for Basil plants in a previous post. However, to fully answer this question, we need to dig deeper and explore the effects of different coloured light and ultraviolet wavelengths (UV) on Basil's growth, flavour, and nutritional content.

Grow light colour and Basil growth

The wavelengths or colours of light play a significant role in how Basil grows and develops. Red and blue wavelengths are particularly important in promoting photosynthesis and enhancing Basil's growth. The relative intensity of each not only affects this growth but can also affect the nutritional content and taste of Basil.

Having said this, however, there is no one single ratio of red light to blue that is ideal for all aspects of Basil development. Changing the ratio can have both positive and negative effects on Basil growth, taste and nutritional content. Therefore, striking a balance between these effects is what we should be aiming for when growing Basil indoors.

Light colour and Basil growth

Multiple scientific studies have shown that the ratio of red to blue light determines Basil's growth or yield. In general, the lower the proportion of blue light, the higher the yield we get from Basil. Taking results of several of these studies together allows us to come up with an approximate light colour ratio for getting the highest yield of Basil crop. An approximately 4:1 Red:Blue light ratio seems to be optimal for Basil growth under LED lighting. However, this does not mean that we should grow it under this ratio as the relatively low blue light level can have some negative effects too.

Light colour and Basil nutritional content

In contrast to increasing Basil crop yield with a decreasing proportion of blue light, increasing the blue component of light leads to increases in essential oils and phenolic content of Basil leaves. These phytonutrients are the health-positive substances that we absolutely want when we consume Basil!

Even more compelling is the improved taste we get with increasing levels of nutritional & health-positive compounds in Basil leaves. Taste-testing studies have revealed that Basil grown under higher percentages of blue light generate the highest rating for taste, aroma, and spiciness. A 2:1 Red:Blue light ratio was shown to have the highest rating for flavour, aroma and spiciness. In contrast, Basil grown under the lower levels of blue light tends to be more bitter. 

Therefore, from a taste perspective, we need to maintain as high a proportion of blue light as possible from the grow light source. This will maximise the level of good phytonutrients and the tastiness of Basil leaves.

Basil grows more compact

One other more minor consequence of growing Basil under higher levels of blue light is that it encourages plants to grow more compactly than they otherwise would. Whether this is a positive or negative is debatable. However, in our opinion, more compact Basil will favour the more desirable leaf growth over the stem and petiole ('leaf stem') growth typical of more elongated plants. So more compact Basil plants is probably something we want.

Basil balancing act

Taking all the above effects together, as Basil indoor gardeners, we have to strike a balance between getting as much edible Basil leaves as we can while at the same time maximising their tastiness and nutritional content.

So ultimately, we have to settle on a level of blue light that is somewhere in-between its two extremes. Based on several research studies, this is likely to be somewhere around a 3:1 Red:Blue light ratio mark which will balance out the yield, taste and nutritional content we derive from a Basil crop.

Red light at night

All plants need a daily period of darkness for health reasons and Basil is no exception. Indeed, studies have shown that when you grow Basil under continuous light, although growth is accelerated, plants start to show signs of ill health after just a couple of weeks.

However, one study has shown that exposure to red light at night can positively impact Basil plant growth without being detrimental to its health. So if you would like to experiment with trying to boost the yield from your Basil crop, then try a low level (~60 µmol/m²/s) of red light exposure overnight.

Ultraviolet (UV) light and Basil growth

As all plants have evolved under sunlight, it is perhaps no surprise that many (if not all) of them are also affected in some way by UV. In general, UV light exposure decreases crop yields in Basil plants, so it is not something that we want too much of.

However, one major positive effect of Basil's exposure to UV light is that it increases the concentration of those healthy phytonutrients that we want in Basil leaves. Crucially, it has been found that short-term UV exposure was better at increasing the phytonutrient content of Basil leaves than long-term exposure.

As a result, it is important to strike a balance between giving your Basil plants a small amount UV to enhance their nutritional content but not so much that it significantly stunts their growth. So how much UV light should you expose your indoor Basil plants to? Based on studies to date, we recommend an hour a day of ~2.5 µmol/m²/s UV-B (we say UV-B as that was what was used in the majority of research studies. However, the effects from UV-B and UV-A are likely to be similar). This level of UV is likely to provide the right balance between maximising Basil crop yield, taste, and phytonutrient content.

Conclusion

As you can see from this post, different colours of light and UV wavelengths can have significant impacts on Basil's growth, nutritional content, and flavour. In particular, the red:blue ratio of light can, most of all, affect Basil's yield. While a lower proportion of blue light can stimulate vegetative growth, higher levels of blue light can enhance healthy phytonutrient content and the tastiness of Basil leaves.

In addition, exposure to red light at night may supercharge your Basil plant's growth, while UV radiation will increase phytonutrient levels even though it may decrease overall crop yield.

Therefore, growers can and should manipulate light colour and UV exposure in addition to setting the light intensity and duration of LED grow lights for Basil plants in order to optimize its production and nutritional quality.

References

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Bantis, F., Ouzounis, T., Radoglou, K., 2016. Artificial LED lighting enhances growth characteristics and total phenolic content of Ocimum basilicum, but variably affects transplant success. Scientia Horticulturae 198, 277–283.

Dou, H., Niu, G., 2020. Plant responses to light. Chapter 9. In: Kozai, T., Niu, G., Takagaki, M. (Eds.), Plant factory – An indoor vertical farming system for efficient quality food production. Academic Press, Elsevier, London, UK.

Matysiak, B., Kowalski, A., 2019. White, blue and red LED lighting on growth, morphology and accumulation of flavonoid compounds in leafy greens. Zemdirbyste Agric. 106 (3), 281–286.

Pennisi, G., Sany!e-Mengual, E., Orsini, F., Crepaldi, A., Nicola, S., Ochoa, J., Fernandez, J.A., Gianquinto, G., 2019b. Modelling environmental burdens of indoor-grown vegetables and herbs as affected by red and blue LED lighting. Sustainability 11 (15), 1–21.

Patel, J.S., Radetsky, L., Rea, M.S., 2018. The value of red light at night for increasing basil yield. Can. J. Plant Sci. 98 (6), 1321–1330.

Sakalauskaite, J., Viskelis, P., Duchovskis, P., Dambrauskiene, E., Sakalauskiene, S., Samuoliene, G., Brazaityte, A., 2012. Supplementary UV-B irradiation effects on basil (Ocimum basilicum L.) growth and phytochemical properties. J. Food Agric. Environ. 10 (3-4), 342–346.

Yelton, M., Byrtus, J., Chan, G., 2017. Better tasting basil grown with LED lighting technology. 2017/04/research. LumiGrow Inc., Emeryville, CA.