Basil is a versatile herb used all over the world. It is easy to grow and beneficial for many purposes. However, it is also susceptible to many conditions, diseases, and pests that may lead to Basil leaves turning yellow.
Causes for Basil Leaves turning yellow
Here is a list of the reasons why basil could turn yellow, and solutions to prevent it.
1) Wrong amount of water
It is important to water the Basil the right way else it could hamper your Basil growth and may also turn its leaves yellow.
Overwatering
The most common reason for basil leaves turning yellow is Overwatering.
Basil is a sensitive herb with very specific water requirements. While the soil needs to be moist, it needs to be well-drained with proper ventilation.
How to avoid overwatering?
If you have an indoor plant, make sure that your container has drainage holes. While watering, as you notice the first drops of water leaking from the drainage holes, you should know that it is time to stop watering.
Another way to check whether you need to water the plant is to stick your finger around 1 to 2 inches inside the soil to check if it is still moist. This is because that is where the roots of basil grow.
The soil that looks dry on the surface might still be moist inside. The top part of the soil tends to dry out fast because of the evaporation from the sun and higher temperatures.
A lot of plant containers have a saucer under them, to hold the water so that the floor doesn’t get wet and dirty.
However, the saucer collects the water that is supposed to drain away, which eventually leads to root rot. It also becomes a breeding ground for mosquitoes and other pests.
How to fix overwatering?
If your plant has turned yellow because of overwatering, you can remove the plant from the wet environment and let it dry for a while. After that, transplant it into another container that has drainage holes and well-drained soil.
Do not keep a saucer underneath your container. Make sure you water the plant carefully after it has been re-potted.
Under-watering
With its very specific requirements regarding water, a basil plant can turn yellow due to under-watering just like it can due to overwatering.
When you provide the plant with less water than it requires, the plant sacrifices some of its old leaves in order to use that water for new growth. That is why the older leaves turn yellow, before eventually dying.
Less water also causes the plant to dry up due to not getting enough water to carry out its natural processes. The wilting plant then turns yellow before dying.
How to avoid under-watering?
As soon as you the soil starts to feel dry, it is time to water it. You can check the soil by sticking your finger 1 to 2 inches inside the soil, and if it feels dry, it needs water.
How to fix under-watering?
If the plant has already dried out and you can see the leaves turned yellow and wilting, water it immediately.
However, just because your basil is under-watered, you cannot compensate by giving it extra water and flooding the plant.
Ensure that you give a normal amount of water in small doses, but at more frequent intervals than you normally would. This would soon revive the plant and make it fresh and healthy again.
2) Disease
Basil leaves can be turning yellow due to a disease. Let us look at some common ones below.
Root Rot
When the problem of overwatering is left unattended for a long time and no measures are taken to save the plant, it will eventually lead to a disease called root rot.
This disease affects plants like basil which require well-drained soil with good air circulation.
It is a fungus that causes the roots of plants to mold. When the roots of the basil are submerged in water for too long, this fungi starts growing on the roots.
This way, the roots start decaying and are not able to absorb the nutrients from the soil that are essential for the plant to grow.
One of the first symptoms of root rot will be the Basil leaves turning yellow and then wilting.
To check whether the yellowing is really due to root rot, you need to check the roots. Rotten roots are brown, slimy, and have a smell foul due to the bacterial infection on them.
How to fix root rot?
If your basil roots do rot, the best option is to remove the plant to keep the rot from spreading through the soil to the other plants. It is also preferable to not reuse the soil, or if you do, to sterilize it before planting another plant in it.
If you still want to try to save your plant,
- Remove the plant by loosening the soil around it and let the roots dry for a few hours.
- Cut off the brown roots to avoid the spread of the bacteria to the other roots.
- Place the plant in a new pot with new soil and avoid exposure of the plant to sunlight for a few days.
Wait for a week to see the results. The chance of survival is not very high, especially if more than half the roots are damaged.
Downy Mildew
Downy Mildew is a disease caused by the pathogen Peronospora Belbahrii. It is a relatively new disease and is quite common among herbs. The disease can be carried through air and water splashes, making it highly contagious.
This parasite thrives in humid environments without any ventilation. The symptoms would include Basil leaves turning yellow with a grey fuzzy underside.
How to fix Downy Mildew?
Because of its contagious nature, the only rational solution is to get rid of the diseased plant if it has spread too much.
If the damage is minimal, isolate the plant immediately and keep it in a relatively dry environment. Manually remove the leaves that are affected by the fungus. Use an anti-fungal water-solution spray to get rid of the disease from your plant.
How to avoid Downy Mildew?
While Downy Mildew is very contagious and your plant can catch it from another plant, there is still a way you can avoid it from ever happening.
Because the disease develops because of extreme humidity and poor air circulation, make sure that your plant is well-drained and the leaves are free of moisture.
This is managed by having proper soil for the plant and watering the plant at its base, rather than on the leaves.
3) Nutrients and Minerals Deficiency
Most herbs do not require a lot of fertilization. Basil, too, is a hardy plant that can grow well even in poor soil.
However, basil still requires a lot of nutrients and minerals to thrive and stay healthy like the minerals potassium, nitrogen, and phosphorous.
A lack of potassium can make the basil leaves turn yellow in the veins. It is hard to spot the lack of potassium. You might need to test your soil to find out.
To fix this problem you can add a potassium-rich fertilizer to the soil which would fill up the deficiency.
Another way is to change the potting soil.
High pH levels in the soil can also make your basil turn yellow. It is because high pH means fewer nutrients, which include nitrogen. Nitrogen is responsible for the green color of the leaves.
The ideal soil pH for basil is 7 – 7.5. The reasons for your soil being alkaline could be old soil, adding alkaline substances to the soil, or using alkaline tap water to water the basil.
The best way to fix this problem is to change the soil. Go for a good potting soil with the ideal pH.
4) Pests
This is one of the worst reasons for me. Here are some of the common pests that can make your basil leaves yellow (or even black)
Aphids: Aphids are one of the most dangerous pests for basil. They are extremely tiny and multiply rapidly. They love most of the herbs, so they can easily spread to other herbs planted nearby.
Aphids suck the nutrients from the leaves. A lack of nutrients will result in the yellowing of the leaves that will eventually wilt and die.
As aphids suck the nutrients, they will cause yellow spots in those places. Aphids also excrete a sticky, yellow, dense liquid called honeydew.
Caterpillars: Many types of caterpillars can be found on a basil plant. These caterpillars dwelling on the plant lead to foliar damage, which includes yellowing of the leaves.
Root-knot nematodes: These pests live inside the soil. They cause galls on the roots and yellow leaves.
Solution for pests
To get rid of pests, there are a few ways you can try.
You can introduce predators which would feed on them and eventually get rid of them.
Neem oil is an excellent solution because it kills most of the pests that grow on basil.
Introducing a companion plant to basil will also help repel pests and keep them away.
5) Temperature and Light
Basil is a sensitive herb that is easily affected by changes in temperature and light conditions. It is a spring-summer herb and requires a warmer climate.
Temperature around 15°C or below will result in stunted growth and pale green or yellow leaves.
Lack of sunlight, too, will result in the yellowing of the leaves. Anything less than 6 hours of adequate sunlight will lead to the basil wilting.
On the other hand, too much sunlight, that is, 10 hours or more of the harsh sun will lead to sunburn and will cause the leaves to turn black.
How to fix the problem of temperature and light?
A windowsill is one of the best places for basil to grow if it receives even some direct sunlight. If not, try the warmest area of the house, maybe near a heater, to keep the temperature optimum for the basil.
You can also create a small greenhouse for the plant, or invest in a grow light that would provide the light and heat required.
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6) Store-bought Potted Basil
A store-bought basil plant once potted cannot be just watered and left on its own.
Within 1 to 2 weeks of you buying the plant and carefully watering it, it may start to turn yellow.
It is normal for such plants to become yellow because they are grown in unfavorable conditions, with a lot of them clumped together in a tiny space. This has the plants fighting for space and the nutrients from the soil.
To fix this problem, repot your basil into a good, bigger container with some good quality potting mix. Water it adequately and provide at least 6 hours of sunlight per day.
7) End of Life
Basil is an annual herb. Most varieties of basil last only for one year. As they grow, they start flowering and once their natural cycle is completed, they die.
As they start flowering, the basil plant directs most of its energy to the flowers and seeds, which leaves little for the rest of the parts.
Because of this, the leaves of the plant start wilting, may turn bitter, and dry out. This process causes the leaves to turn yellow at some point.
Solution
Sadly, there isn’t much you can do to stop the natural cycle of a plant from happening. However, you can certainly delay the process.
Basil can last longer than its life cycle through careful management of the temperature, water, growing conditions in general, and pruning.
When basil is flowering, it is moving towards its end. The last of its energy is spent on its seeds.
However, if you remove the flowers before they have a chance to start growing and producing seeds, you are actually delaying basil death.
While this doesn’t mean that your plant will live forever, it will certainly add more time to its life if you keep on pruning away the flowers before they blossom.
