Basil leaves will turn yellow if they are not getting enough nitrogen, if the plant is being overwatered or is attacked by pests. To help the basil plant to grow new green leaves feed it with liquid nitrogen fertilizer, add a small handful of pelleted chicken manure and you should see new green leaves in no time.
Check the basil plant for aphids or spidermite and trim off the affected leaves. This article will explore the top causes of yellow leaves and what you can do to solve them.
Why basil leaves turn yellow and solutions
Here are the top reasons why a basil leaves turn yellow. Check out each one and see if this might be the cause of the problem for your basil.
1. Lack of nitrogen
Basil plants will naturally have bright green or deep purple leaves depending on the variety but if they lack nitrogen the leaves can turn yellow. The lack of nitrogen can result in a lack of chlorophyll in the leaves which gives them their green color.
Yellow basil leaves caused by a lack of nitrogen is easily solved by giving them a feed of diluted liquid nitrogen fertilizer every 2 weeks over Spring. Add a few handfuls of pelleted chicken manure around the plant for longer lasting nitrogen and your plants will replace old yellow leaves with new green leaves.
Trim off any damaged or yellow leaves and the basil plant will grow new stems with bright green leaves. To prevent this problem happening before planting out your basil, dig through some aged cow or chicken manure through the soil before planting.
2. Lack of light
Basil plants that are not getting enough bright sunlight can end up with yellowing leaves. Basil plants grow best in full sun and if they are getting too much shade they will not have the bright green leaves you would expect.
To solve this problem move potted basil plants out into a bright sunny area in late spring and summer. This will avoid any early spring frosts that can damage leaves. Basil plants are a summer growing herb so bright sunlight is key to tasty green leaves.
Overwatering is a common reason why basil leaves can turn yellow. Overwatering can wash away nutrients particularly nitrogen from the roots of the basil plant. Nitrogen is easily washed out of the soil and is essential for the green leaf color.
Avoid overwatering basil plants by checking the soil moisture before adding more water. Water the basil if it is dry 1-2 inches below the surface. Adding mulch will help to regulate the amount of water that the basil gets as it can absorb extra water and slowly release it to the plant.
Overwatering is more likely to happen to basil planted in pots that have pot trays or are self watering. This is because excess water can sit in the tray and cause the roots to rot. This stops the plant from absorbing nutrients. To avoid this always tip out excess water from the tray after watering.
4. Pest attack
Pest attack can be the cause of yellow or damaged leaves on basil plants. Sap sucking insects such as tiny green aphids or spidermite can damage the plant, reducing the amount of water and nutrients available causing yellow leaves.
Small green aphids can attack basil plants sucking their sap and causing leaves to turn yellow. These insects will attack new growth and can appear quickly in spring and fall. Ladybugs will move in if they are around and eat the aphids.
I always like to treat this pest problem by trimming off the affected leaves and spraying down the plant with water. Spray the leaves with neem oil and wait for 2 weeks before eating the leaves.
Underwatering can cause basil leaves to turn yellow. Basil plants grown in poor, sandy soils that drain quickly can turn yellow due to lack of water particularly when the weather gets hot.
To avoid this problem start by planting the basil plant into improved soil. Always improve the soil in your garden beds first with aged cow manure and compost and mix it through well.
Regularly water your basil and apply a 2 inch layer of straw mulch in the warmer months. Keeping consistent water to basil during hot weather can help to prevent leaf yellowing.
What to do when basil leaves turn yellow
Here are the top 3 steps to follow if your basil leaves turn yellow.
1. Check the soil and water it well
Stick your finger 1-2 inches below the surface of the soil to check the moisture level. Water the plant every 2 days for the next week. If the water is still wet wait until the top layer has dried before watering again.
2. Liquid feed with nitrogen fertilizer
Add dilute liquid fertilizer to the basil plant every 2 weeks 3 times. Do this throughout spring to give them a nitrogen boost which will help the leaves to turn green.
3. Trim off yellow and brown leaves
Remove yellow damaged leaves with kitchen scissors or garden secateurs. This will then encourage the plant to grow new stems and new healthy green leaves.
Following these steps will help a yellowing basil plant to recover and grow new healthy leaves for your cooking at home.
Yellow leaves on Basil | Summary
Basil leaves can turn yellow due to a lack of sunlight, lack of nitrogen, over or underwatering or pest attack. Identifying the issue is the first step to fixing the problem and growing bright green and healthy basil leaves.
Always set up your basil for success by planting them into good quality soil, mulching with sugar cane or straw and watering regularly. A healthy plant will be more resistant to pest attack and even damage from cold snaps in spring.
To prevent yellow leaves from frost damage, keep young basil plants protected in a greenhouse or near a brick wall and then plant them out into your garden bed when the weather is warm.
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