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What Causes Basil Leaves to Turn Yellow

What Causes Basil Leaves to Turn Yellow

The Basil plant is known to be a staple in several cuisines. This plant is a native of the tropical regions in central Africa and Southeast Asia.

The Basil plant has a thick taproot and is known for its herbal leaves that are silky green in color and oval in shape. Its leaves can grow up to 4.3 inches long (11 cm) and 2.4 inches wide (6 cm).


What Causes Basil Leaves to Turn Yellow?

Basil leaves can turn yellow for a number of reasons. Some of them include over-watering, over-fertilizing, diseases, pests, and issues related to soil. The Basil plant requires attention when it starts turning yellow once it develops flowers. This is a sign that it is the end of its life cycle. However, even this issue has a solution, such as pinching the buds before they bloom.


5 Causes Behind Yellow Basil Leaves

1)    Over-watering

Wet soil can cause your Basil leaves to turn yellow. Yellow leaves are a sign that something is wrong within the plant, and in the case of over-watering, the roots start to rot.

This is the most common cause of yellow leaves for many owners because they tend to keep their plants in the kitchen. This makes them tempted to water the plant every day even though it is unnecessary.

Keeping your plant indoors in containers can reduce the drainage of the soil if the pot lacks proper drainage holes. Since the Basil plant breaths through its roots, having them submerged in water can make the roots rot.


2)    Excessively Compact Potting Mix

If your soil is too compact, then it will suffocate your Basil. The soil needs to be airy so that the roots of the Basil plant can breathe.

Your potting soil is considered to be too compact if it has a high amount of clay or silt content within it. Often times this soil is found in a random field or park near you, and this is not recommended as it lacks the nutrients your plant needs.


3)    Downy Mildew Disease

Downy mildew is a disease that is caused by a pathogen (Peronospora Belbahrii), which is similar to a fungus. This is the most common disease found in herb plants such as Basil.

This parasite loves to live on Basil leaves if they are kept in a highly humid environment without proper air circulation. You can spot this on the bottom side of your leaf, and it is black/grey in color, which makes your leaf look dusty.


4)    Lack of Potassium

Potassium is a mineral required by Basil leaves to help them survive. A lack of potassium always causes the leaves to turn yellow, especially close to the veins.

But potassium is not the only mineral required by Basil leaves; they also need phosphorus and nitrogen. Using a good fertilizer is key to a healthy plant.


5)    Wrong pH for the Soil

Alkaline soil, which is high pH soil (above 8), is another reason behind why your Basil leaves may be turning yellow.

Nitrogen is one of the nutrients that are often depleted from the soil once a plant is grown in it. It plays an important role in balancing the soil’s pH and giving your Basil leaves their vibrant green color.

A soil PH of 7 to 7.5 is ideal for Basil leaves. But the Basil plant can also survive in pH levels of up to 8.5.


Solutions for Yellow Basil Leaves


Avoid Over-watering

Basil requires moist soil and not waterlogged soil. If you are unsure about when to water your plant, simply let the soil get a little dry before watering it again.

You can also fix a plant that has turned yellow after over-watering by following a few simple steps.

  • Remove the plant from the pot, and start to loosen the soil around the roots. You can brush off the soil gently by lightly hitting the soil with your hand, and to further help remove the soil easily, let the soil dry up a little.
  • Leave the roots to dry up for one or two hours in the open air.
  • Cut off any roots that look brown. The spread of bacteria is reduced by this method.
  • Place the plant in a new pot with a new potting mix.
  • Avoid keeping the plant under direct sunlight. Keep it under bright indirect sunlight.

Letting the Basil plant’s roots dry up before repotting it will ensure that the plant’s energy goes into recovering the roots rather than producing more foliage. You will have to wait a whole week before you repot your plant.

The chances of survival are low if more than half of your roots have rotted.


Remove Compact soil

The safest thing to do in this case is to replace your soil with a completely new potting mix. There are several premade potting mixtures available, or you can make your own by adding coarse sand, peat moss, and perlite.

New potting soil will only last for up to two years, and sometimes it will only last up to one year. This is why it is important for you to change your soil almost every year.


Get Rid of Downy Mildew

Firstly, you will have to remove your Basil plant from the humid area. Shift it to an area where there is proper aeration. Isolate your plant from surrounding plants so that the rest do not get affected.

Secondly, you have to prune off all the infected leaves. The fungus can spread through tiny pores in the air and can be carried from one place to another through water droplets as well.

This is why one infected plant can cause the rest of the surrounding plants to die.

Another solution is to remove the fungus by using antifungal water spray. You can easily make this spray at home as well.

To make the spray add a tablespoon of baking soda, one tablespoon of liquid soap, one tablespoon of vegetable oil, and 4 liters of water. Mix these ingredients into a bottle and spray the leaves of your plant once a day until the fungus disappears.


Fix Potassium Deficiency

Potassium deficiency can easily be fixed with potassium-rich fertilizer. There are many fertilizers available in gardening shops that have high levels of potassium in them.

You could also simply change the potting soil again, but this is a long and sometimes damaging process. You should never repot or change the soil of your plant until absolutely necessary.


Keep a Consistent pH

The Basil plant requires a neutral pH soil and anything above it or below it is not good for the plant. The biggest issue you will face is with alkaline soil.

Your soil will have high pH levels if you use old soil or if you keep adding substances to the soil. Some people add ashes or lime into their indoor herb’s soils, which is only used for outdoor plants.

Lime and ashes are good for alkaline loving plants, but Basil leaves cannot thrive in alkaline conditions. Anything above pH level 8.5 makes the soil unlivable for your plant.

Sometimes tap water can be the cause of alkaline soil. Many countries do not have a set water pH, and it can range from 7 to 8.5.

This is why it is best to avoid using tap water for your plant.


Frequently Asked Questions About Yellow Basil leaves


Can I eat yellow Basil leaves?

Yellow Basil leaves are safe to eat, but they taste bitter or lack taste due to the yellowing.


Why are there black spots on my yellow Basil leaves?

The presence of black spots can be caused by pests, fungi, thrips, and parasites.