Basil Plant Light Requirements: Key Points
- 1Basil plants should be exposed to a PPFD of at least 180 µmol/m2/s (use the Photone app on your Apple or Android phone to measure PPFD at home if you don't have a dedicated PAR meter).
- 2The optimal PPFD for Basil plant growth is 500 µmol/m2/s.
- 3A PPFD of more than 600 µmol/m2/s can be detrimental to Basil plant growth and can also negatively affect its taste when consumed.
- 4Basil plants should be grown at a DLI of between 13 and 29 mol/m2/s (also measurable with the Photone app).
- 5Basil seedlings should be given lots of light in their first 8 weeks, as this has an outsized positive effect on how vigorously they grow as adults.
- 6Light quantity positively correlates with Basil's phytonutrient content. Therefore, the more light you give your Basil plants, the more nutritious and healthier for you they will be to eat.
Basil is a popular herb used in various cuisines around the world. To grow basil, providing the best light conditions is essential.
How much light does Basil need?
Light intensity is a crucial factor in Basil plant growth and development. It is perhaps no surprise then that research shows Basil plant growth increases with increasing light intensity. However, this only occurs up to a certain level. At a certain peak light intensity, Basil plant growth is then limited by other factors.
So what is the optimal light intensity for Basil plants?
From scientific studies, Basil has been shown to grow well with a light intensity or photosynthetic photon flux density (PPFD) of 180 μmol/m2/s and above. However, the plant grows at its very best at an irradiance of about 500 μmol/m2/s. To check whether your own Basil plants are getting enough light, you can measure PPFD either with a dedicated PAR meter (expensive!) or you can use an app on your mobile device (cheap). Our go-to app is Photone which is available on both Apple and Android hardware.
Going a lot beyond the optimal light level of 500 µmol/m2/s does not encourage greater growth and may even be detrimental to Basil. Indeed, one study in Brazil showed that giving Basil plants 50% shading from the full effects of the sun resulted in larger, more fruitful (in terms of the number of edible leaves) Basil plants.
Another consequence of too much light is that the taste and texture of the Basil leaves can be negatively affected. Studies have shown that increasing the light intensity beyond 400-600 μmol/m2/s leads to Basil leaves that are more bitter and less appealing in texture and colour.
Using DLI to measure whether Basil plants are getting enough light
Another measure that should be used to assess the amount of light given to your Basil plants is the Daily Light Integral (DLI). This is similar to PPFD but also takes into account the amount of time in a day that plants are exposed to light. So, for example, a plant exposed to a PPFD of 300 µmol/m2/s for 18 hours in a day will have a DLI of 19.44 mol/m2/day as the calculation below shows:
18 hours = 64,800 seconds
300 µmol/m2/s = 0.0003 mol/m2/s
=> DLI = 0.0003 x 64,800 = 19.44 mol/m2/day
Basil is classified as a high-light plant since its optimal DLI is above 20 mol/m2/day (that is something like 16hrs of 350 µmol/m2/s of light). However, this does not mean that Basil won't grow well with lower light quantities. Indeed, studies have recommended DLIs for Basil growth of anywhere between 12.9 to 28.8 mol/m2/day. This is especially relevant when growing Basil indoors as you have to balance the costs of artificial lighting and a controlled environment against the return in edible produce.
A good confirmation of the light requirements of Basil can be taken from commercial Basil production where the recommended DLI ranges between 13 and 35 mol/m2/day.
Other reasons to make sure your Basil plants are getting enough light
There are two other points to note when considering how much light your Basil plants need.
Firstly, studies have shown that a constantly high DLI during the first 8 weeks of seedling growth is a must. This is because the yield you eventually derive from plants exposed to lots of light as a seedling is much greater than for those plants that were not. What this means is that you should not assume that a small Basil seedling does not need lots of light just because it only has a few small leaves. Giving it lots of light early on has a multiplying effect on its eventual development.
Secondly, increasing the DLI also affects Basil's phytochemical composition. Studies have shown that the greater amount of light that Basil plants are exposed to, the more they will maximise the amount of healthy phytonutrients they produce. So when it comes time to eat them, plants that have been exposed to lots of light are going to be even more packed with nutrients that are good for us than they would have otherwise.
As you can see, providing the best lighting conditions is essential for growing lots of high-quality Basil. While there is a range of ideal light intensities and light quantities under which Basil will grow well, one also has to consider the balance between yield and quality factors such as taste, appearance, and texture.
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