Strawberry plants like the blues

​​Just about any plant with the right lighting and in the right environment can be grown indoors, but it turns out that determining ideal conditions for growth is not a one-size-fits-all affair. Today, it is pretty well established that different plant species have different needs and requirements, and this happens to be especially true in the realm of lighting where different plant species react differently to different wavelengths of light. This is why it is important to understand the effect of different lighting conditions on a plant species-by-plant species basis. One recent study that emphasises this point looked at the growth of strawberry plants under different kinds of artificial light with some interesting conclusions that might be relevant to anybody thinking about growing their own strawberries indoors.

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​In the study, scientists grew strawberry plants in a growth chamber under either fluorescent neon lights, blue (436nm) LED lights, or red (666nm) LED lighting. They grew 25 plants under each of the lighting conditions set to a constant photosynthetic photon flux density (PPFD) of 100µM / m2 / sec for 78 days with the fruit harvesting period from day 37 to day 59.

As one might expect, multiple characteristics of the plants' growth and the yielding of strawberries were ​monitored including the fresh weight and dry weight of the plants, leaf area, petiole (‘leaf stems’) and flower stem (peduncle) lengths, chlorophyl content, average yield of strawberries, average fruit weight, and ultimately fruit quality (involving such things as flesh firmness, acidity, fruit colour, and the amount of certain phenolic compounds in the fruit like anthocyanins that are healthy for us to eat).

From the study the researchers found that although strawberry plants grown in blue light had higher amounts of biomass, they tended to have much reduced leaf areas and have longer flower stems and petioles. Surprisingly, they also produced significantly more strawberries than the other two conditions. This is in contrast to what one normally associates with flowering plants where red light tends to be more associated with greater flowering and fruit production, while blue light tends to be more associated with vegetative growth. Similar results with supplemental blue light were obtained from strawberry plants in an earlier study (Choi et al., 2015), so this does appear to be a consistent finding.

​Summary of the relative levels of various characterisitics ​of strawberry plants grown under different lighting regimes


​Fluorescent neon

​Blue LED

​Red LED

Fruit yield

​​Control

​Greater yield

​Smaller yield

Biomass

​​Control

​​Higher Biomass

​​Similar to control

Leaf area

​Control

​​Less leaf area

​​Similar to control

​Chlorophyll content

​Control

​​Lowest

​​Lower than control

​Anthocyanin level

​Control

​Lower than control

​Lower than control

Two aspects of the study should be noted here. Firstly, in ​each of the growing conditions of the experiment, the yield of strawberries was considerably lower than what one sees from strawberry plants grown outdoors. However, one has to remember that none of the lighting conditions in the experiment involved full spectrum lighting or lighting that is considered to be optimal for plant growth and fruit yield. This study simply focussed on trying to dissect out the role of different wavelengths of light on the growth of strawberry plants. The second point to note is that the increased biomass of the plants exposed to blue light may have simply provided greater plant resources to produce the higher yield of strawberries as opposed to having a direct effect on flowering and fruit production. Nevertheless, the study clearly shows that higher blue light levels applied throughout the life of strawberry plants leads to higher fruit yields.

If you are wandering about the quality of the strawberries under blue light, then it is interesting to note that the fruit in all three lighting conditions ​showed similar results ​in most of the quality control tests that the researchers carried out. However, anthocyanin levels were seen to be reduced in the LED lighting conditions (both for blue and red lighting) compared to growth under neon lights, but the relevance of this is debatable since once again in any optimised real indoor growing set up, single wavelengths of light would not be used alone to grow the plants.

Image of strawberries

What should an indoor gardener learn from this study?

If you are an indoor gardener and you are planning to grow strawberries indoors, then increasing the amount of blue wavelengths could help increase the yield of strawberries that you can obtain from your plants. Consequently, indoor gardeners might well be advised to test increasing amounts of blue light applied during a strawberry grow to see if there are any positive effects in their particular setup. Of course, one must not forget that in order to maximise plant growth and health, other light wavelengths like red light are still required for healthy plant growth and a healthy yield, and the extra blue light should merely be added on top of the base grow lighting.

​Reference