Reasons why basil leaves are yellow

basil leaves are yellow

Basil is a member of the mint or Lamiaceae family. Basil plant is a well-known herb because of its sweet-spicy flavor, making it popular for use as a culinary herb. The mint family is a well-known herb, and all the plants have a wonderful aroma that you can use in your kitchen. 

Plants are prone to attack by pests and diseases, and one major problem with this plant is that the basil leaves are yellow. Like other plants, if you find this problem in your herb, there is a reason for the yellow leaves in basil. It’s not like it’s resistant to problems. 

Many reasons cause the basil leaves to turn yellow, including thought reasons such as overwatering and overfertilizing. Don’t the plants need all the water and fertilizer they can need to grow? No! That statement is false. Plants require only a tiny amount of water regularly, and they will grow into healthy plants. 

The secret to a successful season is patience and attention to your plants. Fortunately, we can help you identify why basil leaves turn yellow. With the correct information, you will have a healthy plant ready for use at the end of the season. 

basil leaves are yellow

Why basil leaves Are yellow?

As we have said, there are many reasons your plant can have yellow leaves. Let’s look into these problems and find solutions to them.   

Improper Watering

Improper watering can be classified into underwatering and overwatering. When basil leaves turn yellow, it is caused by overwatering the plant. When you water the plant with more water than is required, water remains stagnant in the soil, and as a result, it causes stress to the roots. 

When the roots and under stress, they start to rot, which will end up killing a plant. So, how does this relate to root rot? When the roots are rooting, they stop making enough food that can sustain the plant, and as a result, the leaves start to wither. However, you can say, when the leaves start to turn yellow in basil, it’s a sign of stress on the roots. 

The first symptom you will notice when the roots start having stress is the yellowing of leaves. How does excess water cause roots to rot? When overwatering, the plant and water stagnate at the bottom, submerging the roots and making it hard for them to breathe. Once the root doesn’t have enough air, bacteria thrive under the conditions. And because the basil plant has no access to fresh gas, the roots start decaying, and eventually, the plant suffocates. 

The best way to know if overwatering is the cause of yellow leaves is to check whether the roots are healthy or rotten. Healthy roots are white with a bit of hair, while rotten roots are smelly due to the bacteria, slimy, and brownie. 


Once you find out that your root is rotten, throwing the whole plant away is better. However, if you want to salvage it, here are steps to take:

  • Remove the plant from the point and the soil around the roots gently. Hit the root gently on your hand to detach the soil from the root. 
  • Place the root in the open air for 1-2 hours to dry.
  • Remove all the rotten roots by cutting them to avoid the spread of bacteria. If all the roots are rotten, you can’t help the plant any longer. 
  • Place the root in fresh potting soil and a new pot.
  • Keep the plant in a cool environment away from direct sunlight to ensure the plant recovers without the stress of making food for the rest of the plant. Sunshine starts the process of photosynthesis, and if the root is yet to heal, it can induce more stress. 
  • Note the changes after a week or two, and then you can take it out into the sun. Chances of recovery are minimal, but in some cases, it can recover. 

Tips to prevent overwatering

Firstly, use the saucer test. This test involves placing holes at the bottom of the pot. The holes help to drain excess water in the soil. When watering the plant, you see the first drop of water out of the hole, which means it can no longer hold water. Stop watering after the first drop. The saucer test ensures that water doesn’t stick to the bottom of the pot. 

Secondly, you can use the finger test. This test involves sticking your finger into the soil to check if it’s moist. You use the finger because it goes to the level of the root. You can’t check with your eyes because the surface might be dry, but a few inches below, the soil is moist. 

Not enough light

Plants use sunlight to make food in the process of photosynthesis. As a result, the leaves become green through this process, although some plants don’t turn green. But, because we know basil doesn’t have yellow leaves, it becomes green due to photosynthesis. 

When there is less access to sunlight, and the plant doesn’t make enough food, it can result in the leaves turning yellow. Basil grows in an area with warm temperatures and access to direct sunlight for more than 6 hours to ensure the plants don’t start wilting. Also, ensure you don’t expose it for more than 10 hours because it can scorch the leaves. 


Ensure that you have your plant in an area where it can access direct sunlight for 6-8 hours per day. If it’s an indoor plant, place it by a window facing the south, or you can use supplement lighting. 

Cool temperatures

Like exposure to the sun, the temperatures are a key factor when checking the reasons for yellow basil leaves. Since it’s a plant that likes to grow in warm areas, any sign of cold conditions will start turning yellow and even die during the winter. 

When the surrounding temperatures are below 15 degrees Celsius, the plant will start stunted growth; after 2 to 3 days, the leaves will turn yellow. 


Always ensure the temperatures around the plant don’t go below 20 degrees Celsius. If it happens, you can use external equipment to heat the room to the required temperature for the plant to survive. 

Fungal disease (Downy Mildew)

Plants are prone to attack by diseases. But, since all diseases are different, they attack each plant differently. For basil, when Downy Mildew attacks it, the leaves start to turn yellow. 

Downy Mildew is caused by a pathogen called Peronospora Belbahrii. It’s a common pathogen that attacks herbs. This pathogen attacks the leaves directly when the area is humid and doesn’t have enough air circulation. For instance, the pathogen will attack the plant leaves if you place your basil plant in a closed room. 

To identify if it’s downy mildew, check the lower part of the leaf; it has black or grey spots that look like dust. The black or grey spots on leaves will then turn yellow, and the leaves start to die.


There are various ways you can solve this problem. First, give the plant enough spacing within other plants to ensure proper air circulation. 

Secondly, remove the plant from a humid and damp area into a room with proper air circulation. If the plant is already affected, isolate it from the other plants. Then, remove the affected leaves because the fungus can spread through the tiny pores or the water droplets. Whichever way it gets to the unaffected leaves, it can affect them. 

Finally, you can use an antifungal water solution to spray the leaves. The water solution includes a mix of:

  1. 1 tbsp of baking soda
  2. 1 tbsp of Castile soap
  3. 1 tbsp of vegetable oil
  4. 4 litres of water.

Mix the solution thoroughly before pouring it into the spray bottle. Then spray the solution on the affected leaves once a day until the black-looking dust or dirt starts to disappear. 

Insects and Pests

The most dangerous insects that attack the basil plant are Aphids. Aphids are tiny animals that can stay on your plant for weeks without you noticing. Once they appear on a plant, they can multiply rapidly. 

These insects like eating planting, and if you are not careful, it can affect other herbs on your farm. They like sucking the juice from the plant, leaving spots on the leaf if they are in large numbers. Sucking the juice leaves the leaf with little to no nutrients; as such, the leaf starts to turn yellow, wilts and dies. 


To make sure it’s aphids making your basil leaves turn yellow, check the leaves if they have tiny brown spots. When aphids suck the nutrients off the leaf, it leaves it dry, and the spot turns brown because of a lack of nutrients. 

To prevent aphids from attacking your plant, ensure that it is in good soil conditions and that you provide it with consistent and adequate watering. Overfertilizing the plant only attracts aphids. 

To eliminate the insects, you can use these methods:

  • Cut off the affected leaves from the plant
  • Use natural enemies of aphids such as adult lady beetles, lacewings, and parasitic wasps. These insects eat aphids as a source of protein; thus, if you have them in your garden, you can minimize the attack on your leaves. 
  • Remove insects using insecticides. You can use solutions such as insecticidal soaps, neem oil, or horticultural oils. Spray them when the sun rises and sets every 7 to 10 days.

Lack of nutrients

A plant requires enough nutrients from the soil for it to be healthy and free from diseases. Nutrients include fertilizer, microorganisms, potassium, and soil pH.

For starters, fertilizer is the key nutrient required for any plant. However, too much or too little fertilizer can affect plant growth. Applying too much of it can cause the leaves to turn, which turns them yellow or brown. You can notice this if the lower leaves are the ones turning yellow. 

Microorganisms are found in the fertilizer; thus, if you under fertilize, your plants will lack organisms to create the required food. Lack of enough food will cause the plant to start wilting and that turns the leaves yellow. To differentiate this from overfertilizing, in a plant that has more fertilizer, the fertilizer will be seen on the surface of the soil and the leaves on the lower side of the plant are the only ones to turn yellow. 

Potassium is another deficiency that can cause the basil leaves to turn yellow. This mineral is present in the soil and is found in fertilizers. So, if you apply the requirement amount of fertilizer, you will have all the requirements to grow a healthy plant. To know if it’s potassium deficiency, you can test the plant soil. You can use the Luster leaf test that you can purchase from Amazon. 


Plant need enough nutrients to make their own food and be strong enough to fight off pests and diseases. However, the lack of those nutrients makes the plants vulnerable and are likely to die. 

The best way to save an overfertilized plant is to remove the yellow leaves, i.e. those affected. Then try to remove the topsoil which has more fertilizer. Ensure you don’t touch the roots or damage them when removing the soil. Add fresh soil to cover the removed soil, and then water the plant continuously to remove the excess soil fertility. 

For the plant that has deficiency of potassium, you can add it through potassium sources such as kelp meal, wood ash, greensand, manure, or all-purpose fertilizer.

Compact soil around the plant

This might not be a major reason for basil leaves turning yellow, but it’s something likely to happen. It occurs when the soil around the plant is compact and does not allow for air circulation in and out of the soil. As a result, the roots are likely to die from suffocation. When the roots die and there is no enough food for the plant, the leaves will turn yellow, wilt, and then die. 


Just as we discussed earlier, it’s not easy to recover a plant with dead roots, but you can try. Cut off the dead roots leaving only healthy ones and change the potting soil. Also, ensure the soil is loose and free to ensure proper air circulation.


Does basil require full sun?

Yes, basil plant require direct exposure to the sun for 6 -8 hours per day. If you expose it to more than 10 hours, the leaves will get burnt. 

Are Yellow basil leaves still good?

No, once you spot yellow leaves on your basil plant, start to check for a problem. Once you find the problem, treat and at the same time cut off the leaves to avoid spreading to healthy leaves. 

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