Basil is a leafy green aromatic herb and a popular food seasoning ingredient. Some of the popular varieties include sweet basil, Thai basil and Greek basil. Homeowners usually cultivate it indoors or in backyard gardens. Basil may also be prone to yellowing and discoloration for certain reasons. In this article, you can get to know why basil leaves turn yellow and how to prevent this.
Basil Leaves Turning Yellow: What Are The Reasons?
These are the reasons basil leaves may turn yellow:
1. It may be due to overwatering.
Basil plants prefer full sun and well-drained soil. If they are turning yellow you may need to re-evaluate your watering schedule. Since basil likes well-drained soil, you should water when the top inch to two inches of soil feels dry. You should be able to test this easily by inserting your finger an inch into the soil.
Consider soil drainage if you are growing basil in containers. The planters should have drainage holes to avoid excess water from becoming stagnant.
2. It may be due to diseases such as root rot or downy mildew.
Root rot can affect plants, like basil, that prefer free-draining soil. Root rot can be bacterial or fungal and causes the roots to suffocate and die. While there is no remedy for this, you can remove the affected plant and separate it from the healthy plants so the disease does not spread through the soil.
Downy mildew is another disease that causes leaves to turn yellow with a grey, fuzzy underside. This disease, a plant parasite, prefers a moist environment with low ventilation and humidity. Therefore, always water at the base of the plant and keep leaves free of moisture to prevent your basil plants becoming affected with downy mildew.
Separate affected plants from the rest to preserve the other healthy basil plants.
3. It could be a nutrient deficiency.
Basil leaves may also turn yellow because of nutrient deficiency. To remedy this, try to mix a slow-release fertilizer with the soil when you first plant the herbs. If the growing season is longer than six months, be sure to fertilize again. If you are planting the herbs in small containers, try to add fertilizer on the third month, especially if you water frequently.
Potassium deficiency could result in leaves turning yellow between the veins. Basil plants need minerals to survive, and this includes potassium as well as phosphorus and nitrogen. You can correct this by adding a potassium-rich fertilizer to your plants’ soil.
4. It could be due to a pest infestation.
If, as well as yellow leaves, you notice a black, sticky substance on the back of the leaves, or white bugs, you likely have a pest problem. Aphids and mealybugs can attack plants including basil.
Here are some things you can do if your basil plants are infested with pests:
- Introduce a predator
Insects like ladybugs and green lacewings feed on aphids and mealybugs. You can purchase them from your local nursery or you can attract these insects, particularly ladybugs, by growing plants and flowers that ladybugs like. You may also add a water source to help attract them to the garden where your basil plants are growing.
- Use neem oil.
You can also eradicate pests by using neem oil in your garden. Apply this organic oil to infested plants for best results.
- Eradicate allies such as ants.
Ants feast on the secretions of pests, called honeydew, a sugary, sticky substance. To eradicate pests you also need to eradicate ants using ant-killing food or by treating ant hills and sprinkling the soil with cinnamon.
- Plant some companion plants.
Consider planting your basil plants near zinnias and garlic that release odors that pests dislike. Other companion plants include geraniums, chrysanthemums and mint.
5. It could be due to a potting mix that is too compact.
Compact potting mix could endanger and suffocate your basil plants since they require fluffy soil for gaseous exchange. To avoid this, use a good quality potting mix which is airy, fluffy and enriched with nutrients.
6. It could be due to the wrong soil pH.
Yellowing basil leaves may also be due to high pH levels of eight and above. Nutrients become less available, such as nitrogen which is responsible for the green color of plants. To correct this, you need to change the soil to a good quality potting soil.
Aside from the issues mentioned above, basil plants are also sensitive to temperature and light conditions. Ambient temperatures around or below 60 degrees Fahrenheit stunt the growth of basil plants resulting in pale green or yellow leaves. To avoid this, ensure that your plants receive direct sunlight, or place them in a small room with a heater to replicate the atmosphere of a greenhouse.
Conclusion
Basil plants are valuable kitchen essentials that have plenty of health benefits. However, they can also be prone to yellowing because of overwatering, diseases like root rot and downy mildew, nutrient deficiency, wrong soil pH, or pest infestation.
Image: istockphoto.com / OlgaMiltsova