The 3 Reasons Why Your Purple Basil Is Turning Green


Red Rubin Basil: a well known purple basil variety that might turn green – Photo of Forest and Kim Star

Purple basil is a beautiful herb that very likely you have as an ornament in your house. However, as you might have experienced, its intense color might fade. Do not despair, this article has you covered with science-backed up information and remedies if this happens.

Hence, why your purple basil is turning green? Purple basil has the tendency to turn green because of the lack of anthocyanin, the pigment responsible for the intense purple color. The level of this pigment can change due to:

  • Pigment fading: lack of light
  • Pigment Inheritance: purple basil generate green-purple offspring
  • Hybrid Green-Purple: basil is purple and green by nature

Now you know that the lack of a particular pigment is responsible for this color change. However, you need to understand why this is happening and, as a consequence, what you can do about it.

Purple Basil Turning Green? Pigments And Type

Purple basil can show green colors either because of an inadequate light level of pigment, pigment inheritance, or because it is green and purple by nature. Let’s try to understand more of these three cases.

Pigment Fading

The number one reason that purple basil fades to green color is due to light. You need to know that the intense purple color you love is given by the presence of a plant pigment called anthocyanin. For more, you can read this detailed scientific publication from Purdue University, USA.

Such pigment (in 9+ varieties, source) is present also in many other basil varieties (like Rubin, and Dark Opal) and other plants-fruits (such as purple cabbage, cherry, blood orange, etc…). This pigment, indeed, is also responsible for red and blue color.

This pigment is naturally produced by the plant itself. More precisely, purple basil produces anthocyanin as a response to external stress, as discussed in this study from the University of New Zealand.

Contemporary research, in contrast, has begun to show that the pigments can significantly influence the way a leaf responds to environmental stress. Anthocyanins are pigments produced in response to stressful situations. These include drought, UV-B, heavy metals, as well as resistance as a reaction to herbivores and pathogens.

Source

The more anthocyanin produced, the more dominant the purple tone of the leaves will be in purple basil. Alternatively, if anthocyanin production is low, the chlorophyll, naturally always present in the herb, will dominate. As chlorophyll is green, the lack of anthocyanin will make your purple basil turn green.

Hence, the real secret to keeping as long as possible your basil purple is on light management as the light is directly related to anthocyanin production.

This has been highlighted by recent research done by the Journal of Agricultural and Food Chemistry, where a purple ornamental grass called Rubrum was studied. The main finding is that the stronger light exposure is, the stronger anthocyanin production in a plant will be.

This is a concept that can be tied to any anthocyanin-dominant plants such as purple basil. The more light that purple basil is exposed to, the richer of a purple hue it will typically maintain. If the basil plant doesn’t get enough light, it’s likely to revert to a green tone.

Because natural light exposure is related to seasonal changes, you might notice your herb losing its purple tone during autumn-winter. Indeed, purple basil on your windowsill during the long summer daylight hours is more likely to keep its anthocyanin-dominant coloring than in the winter.

Pigment Inheritance

Purple basil might originate new leaves with a partially (or totally) green color. Indeed, as detailed in this study from the study from Purdue University (quite active on the field), the inheritance of the purple pigment (anthocyanin) is quite unstable on basil.

For you, this means that the purple basil seeds you quite likely have bought have a chance of giving a basil plant that presents both green and purple leaves. However, if this is the case, the seller should warn you for providing this percentage. In the Purdue University study, for instance, a 34% probability of having green basil was provided by the seller.

How to differentiate if it is a lack of light or a genetic problem? As shown in the Purdue University study (picture if here) in case the reasons are genetic, some leaves are likely to presents purple and green patches on them. Nothing to worry, this is totally normal, and your herb is healthy and safe to eat.

In case the problem is a lack of light, the majority of the leaves will gradually fade away in color from purple to green.

Hybrid Coloured Basil

This is more confusion than a real problem. Indeed, some basil types present by nature purple and green colors in the same plant. This color duality might involve leaves, stems, or both.

As discussed in this Hawai University study, among the hundreds of basil species, the ones that, by nature, present both green and purple leaves are:

  1. Anise
  2. Licorice
  3. Purple Bush
  4. Tulsi or Sacred
Example of purple-green basil – photo from Kim and Star

Hence, if the seller defines one of the above basil types as purple, you now know that they are both purple and green in color. However, this might not be a problem for you. Indeed, quite a few gardeners find this dual-colored herb even more attractive than its uniform purple counterpart.

Can You Keep Your Basil Purple?

The good news is that it is possible to keep your basil purple under the proper care. This, of course, applies in case the reason is due to a lack of light. For the other 2 cases (pigment inheritance and hybrid colored basil), there is nothing you can do.

As for light, there are a few different methods that can help keep your basil purple. Having a chat with a few indoor gardeners, I found out that making sure the plant gets at least six hours of sunlight every day is vital to keep the purple color healthy.

Increasing the amount of sunlight that a plant gets can be as simple as:

  1. Changing the location: perhaps, due to its ornamental role, you placed it in the middle of the room, on a table, or far from a natural source of light. Place it close to a window or direct sunlight. If you are operating in a greenhouse (you can build one at home yourself), make sure the glazing material is clean.
  2. Grow light: if you, like me, live in a country with just a few hours of sunlight during winters, your plant might still survive but very likely will lose its color. If you really want to keep it purple, you can provide those extra hours of light missing (or the whole 8 hours) through a grow light. If you want to know more about what a grow light is, tips on how to choose one on a budget, and the best grow light in the market, just have a read to my grow light guideline and best grow light choice.

    Indeed, in addressing the purple basil turning green, grow light ensures the long light exposure needed (and impossible, naturally, during winter) and provides the right “plant-quality.” Indeed, indirect light (this is the light your herb receives as bounced back from furniture) or low light isn’t going to stimulate as much anthocyanin production.

    This is demonstrated by the experiments performed by Andrei Lobiuc from Stefan Cel, Mare University. He shows that artificial light gave by a combination of blue and red (in 80-20 ratio) almost doubled the pigment concentration in basil compared to ordinary white light! High-pressure sodium lights – often shortened to HPS lights – and LED lamps are the most effective choices for this job.

    Both of these bulb types are viable options, but LED lights are often favored because they consume less energy than HPS lights. This will save money in the long term as detailed in this money guideline on grow light. LED lights also produce less heat, so they won’t affect the temperature of your plants while they provide additional light. They also recommend adjusting the light intensities and the most expensive, even color type.

Keeping your basil’s health high and stress levels low can also promote healthy development. This implies more leaf to make your ornamental plant even more impressive and, why not, for harvesting and eating purposes. Purple basil is used in a large variety of recipes. Making sure to keep the soil moist, using the correct container size as discussed in this article and pruning regularly. For more, just have a look at 21 pro tips to grow massive basil indoor.

Purple Basil To Green? Does It Taste Good?

Luckily, while they may not have the same appearance, the green tone that purple basil might take won’t affect their flavor. Indeed, as many home gardeners reported here, the change of color in purple basil is a mostly aesthetic problem. Hence, go ahead with your favorite recipes.

As you might know, purple basil presents a more heavy clove taste, definitely less sweet than common Genovese basil. However, this makes this ornamental basil variety also widely adopted in cooking.

What is Purple Basil?

If purple basil is for you basil with purple leaves, then this might not be totally true. Indeed, as also science demonstrated totally purple basil, might come out the green in color in case of pigment inheritance problem.

Purple basil is one of the seven more common commercial basil cultivars. A cultivar is simply a category of plants that show similar features. This means that purple basil includes a large variety of basil types. The most commons are:

  1. Amethyst basil: This is a particular type of purple basil with the darkest tone (almost black). It belongs to the Genovese family (the same you use for your pesto) and can grow up to around 20 inches (around half a meter) in the best conditions.
  2. Dark Opal: this is by far the most well-known among the purple basil types. It presents an intense purple color, and it is generally shorter than amethyst, with a height of max 16 inches (40 cm).
  3. Red Rubin: This is one of the tallest purple basil varieties with a height of around 27’’ (70cm). This has been originated by crossing with Dark opal.
  4. Holy Sacred Red: This is a variety of holy basil, famous for being part of the Hindu religion and so worshipped in India and useful as a mosquito repellant and can grow up to 20 inches (half a meter)
  5. Osmin Purple: this purple basil variety is known among gardeners to have smaller leaves than others. Its purple leaves are almost as dark as the Amethyst variety. It can grow up to 20 inches (half a meter)
  6. Purple Ruffle: the name is due to its curled leaves edges that are, indeed, ruffled. This variety is obtained by selective crossing between dark opal (purple) and Green Ruffles (green) to take the leaves aspects of the Green Ruffle but the color of the Dark Opal. As the others type it can grow up to 20 inches (half a meter)
  7. Red Rubin Purple Leaf: as the name suggests, this purple basil presents an attractive purple/red color. It can grow slightly taller than its purple counterparts (up to 3 feet, around a meter). As other purple varieties, this has been developed from Dark Opal.

Purple Basil vs Green Regular Basil: Differences

Purple basil is a low-maintenance herb that can be grown either inside or outside. As you saw before, the name “purple basil” in reality, include a large variety of herbs with leaves generally ovular with a speared tip measuring at about .7 to 1.2 inches (2 cm to 3 cm) wide.

Generally, purple basil is small and grows in long bunches. The plant also tends to sprout tiny flowers of different colors depending on the variety. Still, many growers find that pinching these flowers off encourages leaf growth as detailed discussed in the 21 tips to grow massive basil. The majority of purple basil varieties have a spicy anise fragrance with a taste similar to clove.

The growing process is identical to more common green basil. It needs ideally 8 hours of sunlight (at least 6 direct), a well-fertilized soil and (ideally to thrive) and the ambient temperature of 21C. It does not tolerate “wet feet,” as gardeners say. This means do not soak the soil leaving their roots (the feet) wet for a long time. Otherwise, this moist environment can trigger the growth of those harmful bacteria responsible for root rot.

By comparison, Genovese basil – also referred to as common or sweet basil – is vibrant green with ovular, flat leaves around 2 to 3 inches (5 cm to 7.6 cm) wide. It grows as tall as 24 to 30 inches (60 cm to 76 cm). According to the University of Vermont, this is the most commonly grown type of basil and, very likely, the most sold in the world. Its great aroma popularity in recipes is the reason.

When full-grown, basil has a sweet flavor with a hint of spiciness. Their fragrance is slightly sweet as well. This type of basil starts to germinate in only 5 to 10 days and matures in about four to six weeks.

Can You Prepare A Pesto With Purple Basil?

There are plenty of tasty dishes that you can make with purple basil as soon as it’s mature. Good news, you can make pesto. The process is absolutely identical to the one of the green basil. You can watch the video below for an example.

You need to know, however, that purple pesto often has a strong savory flavor with an accent of clove and peppery/spicy taste. I do personally love purple pesto, but a few friends of mine complained about it. Hence, it might not be a right choice for everyone, but please try at least once. It is not a bad idea to add one or two teaspoons of table sugar to counteract the bitterness.

In case you do not like a purple pesto, do not forget that those tasty leaves can be used in a large variety of dishes. In Yummy.com I found more than 11 thousand recipes where purple basil was one of the ingredients. Don’t be intimidated by the deep hue of the basil, either! These recognizable leaves are delicious and will give you an aesthetically unique dish as well on top of being amazing ornamental plants.

Further Questions

Does purple basil contain antioxidants? Yes, purple basil contains a significantly higher concentration of healthy antioxidant due to the presence of the pigment

Can purple basil be used in vinegar? Yes, purple basil is often placed inside a bottle filled with vinegar in order to create a flavored dressing ideal for salads

Further Readings

21 Tips to grow massive basil indoor – https://yourindoorherbs.com/21-easy-tips-to-grow-massive-basil-indoor/

How you can propagate your basil, and any herb, by cutting – https://yourindoorherbs.com/3-easy-steps-to-propagate-by-stem-cuttings-free-herb-supply/

How you can save supermarket herbs – https://yourindoorherbs.com/how-to-make-supermarket-herbs-last-for-months/

Andrea

A young Italian guy with a passion for growing edible herbs. After moving to the UK 6 years ago in a tiny flat, it was impossible to grow herbs outside. So I start my journey in growing indoor and so I decided to share my knowledge.

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