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Why are My Basil Leaves Turning Yellow – 10 Causes and Fixes

Why are My Basil Leaves Turning Yellow - 10 Causes and Fixes

Gardeners simply can’t stand it when their plants show worrying symptoms such as yellowing, wilting, or drying leaves. But what can one do about it?

It’s all about catching the factors: sometimes, it has to do with watering and issues associated with watering. Other times, it has to do with cultural practices and even external conditions such as temperatures.

Today, we’ll look into the 10 most common reasons why basil leaves turn yellow – and what the corresponding solution is!

Reasons For Yellow Basil Leaves

Reasons For Yellow Basil Leaves
Image by Boston.com

Basil leaves turn yellow due to overwatering, underwatering, poor soil drainage, and root rot. Yellowing basil leaves are also caused by pests, diseases, extreme temperatures, and inadequate sunlight.

And sometimes, basil leaves just age naturally, turning from green to yellow to brown. Let’s check each factor in greater detail!

Overwatering

Overwatering
Image by Gardening Channel

How to Fix: Water adequately and ensure proper drainage.

When soil gets more water than the basil needs, it’ll lead to the soil retaining too much moisture. This can be a bit of a problem especially when the plant can’t absorb the amount of water or the soil isn’t able to drain the amount quickly.

Since basil plants do best in well-draining soil, they can easily drown from too much water around their roots. This causes a decline in plant health, leading to yellowing leaves.

On top of that, overwatering can lead to other complications, which we’ll discuss later.

Solution: Water adequately and ensure proper drainage.

FactorInformation
DifficultyModerate ●●○○○
SpeedGradual improvement with adjusted watering
Materials NeededWell-draining soil, perlite or sand (if necessary), container with drainage holes

Since the main reason is too much water, you have 2 options: water only when the topmost inch of soil is dry and improve the soil texture for better drainage.

Let’s start with the first. Allow the topmost layer of soil to slightly dry out before watering so that the roots of your basil won’t get overwhelmed with too much moisture.

To complement your watering, make sure that the soil of your basil is well-draining. To get this right, mix in some perlite or sand as necessary.

On top of that, double-check that your container has enough drainage holes to allow water to pass through.

Underwatering

Underwatering
Image by Plantophiles

How to Fix: Water adequately on a regular basis.

It’s as simple as it sounds: the basil plant didn’t receive enough water and now it’s drying up with yellowing leaves due to dehydration and stress. As with most plants, basil requires consistent moisture to thrive and can wilt and discolor when deprived.

Aside from wilting and yellowing leaves, watch out for dry soil and an overall unhealthy plant appearance. Just make sure to water adequately – too much and too little can have similar results.

Solution: Water adequately on a regular basis.

FactorInformation
DifficultyEasy ●○○○○
SpeedModerate improvement may take a few days to a week, depending on the plant’s condition.
Materials NeededWatering can, well-draining soil, organic mulch, moisture meter (optional).

To address underwatering, check the moisture level in the soil frequently, especially during warmer periods or if the basil is in a container. When the top inch of the soil feels dry, water the plant thoroughly, allowing the water to reach the root zone. 

Ensure proper drainage in the pot or planting area to prevent waterlogged soil, which can exacerbate problems. Consider adding a layer of organic mulch around the basil plant to help retain moisture and regulate soil temperature. 

Check the plant for any signs of improvement and adjust the watering frequency based on its specific needs.

Poor Soil Drainage

Poor Soil Drainage
Image by Amazing Herb Garden

How to Fix: Use well-draining soil and improve drainage.

This is another issue that’s worsened by water and watering activities. When the soil is compact, it retains too much water and doesn’t allow the moisture to drain as quickly as it should.

When soil doesn’t drain well, excess water accumulates around the roots, leading to oxygen deprivation and root rot. Basil plants thrive in well-draining soil, and poor drainage can cause stress and nutrient deficiencies. 

Other signs of poor drainage include waterlogged soil, a foul odor, and wilting leaves despite seemingly adequate watering. 

Solution: Use well-draining soil and improve drainage.

FactorInformation
DifficultyModerate ●●○○○
SpeedGradual improvement in basil’s health as it may take a few weeks as the soil adjusts and drains better.
Materials NeededWell-draining soil or soil amendments (perlite, sand), container with drainage holes, organic mulch.

Fixing the texture of the soil is key to making it drain well. Look for and use well-draining soil or amend existing soil with materials like perlite or sand. 

These amendments enhance aeration and water movement in the soil. If the basil is in a container, ensure the pot has drainage holes to allow excess water to escape. 

Also, elevate the container slightly to further encourage drainage. As much as possible, avoid compacting the soil around the basil’s root zone. 

Applying a layer of organic mulch can also assist in regulating moisture levels. Regularly check the soil’s moisture content and adjust your watering practices accordingly.

Nutrient Deficiency

Nutrient Deficiency
Image by vlr.eng.br | Daily Update

How to Fix: Feed your basil with a balanced, water-soluble fertilizer, preferably one with a higher nitrogen and potassium content.

Chlorosis is the term for leaves that turn yellow due to nutrient deficiency. If your basil leaf is yellow but otherwise healthy, then it could need more nitrogen or potassium in its feeding.

The chlorosis in your basil leaves tends to show up in the larger or older leaves, whether grown in the ground or in pots. Watch out for uniformly yellow leaves as they’re the signs of nutrient deficiency. 

Nitrogen is essential for the synthesis of chlorophyll, the green pigment responsible for photosynthesis. Potassium plays a crucial role in various plant functions, including photosynthesis, enzyme activation, and water uptake.

Left alone and without any nitrogen or potassium, your basil may become stunted over time.

Solution: Feed your basil with a balanced, water-soluble fertilizer, preferably one with a higher nitrogen and potassium content.

FactorInformation
DifficultyModerate ●●○○○
SpeedGradual improvement may be observed over several weeks as the plant uptakes nutrients.
Materials NeededNitrogen-rich fertilizer, watering can, organic matter (optional), gloves (optional).

Luckily, addressing the nitrogen and potassium issue is quite simple. Just pick a water-soluble fertilizer with a higher nitrogen and potassium content such as 10-5-10, indicated by the three numbers on the fertilizer label (N-P-K ratio). 

The N-P-K ratio stands for nitrogen, phosphorus, and potassium. Dilute the fertilizer according to the manufacturer’s instructions and apply it to the soil around the basil plant, taking care not to over-fertilize. 

Water the plant thoroughly after application to help the nutrients penetrate the root zone. Repeat this process every few weeks during the growing season, following package guidelines for frequency. 

You can also try incorporating organic matter into the soil to provide a slow-release source of nitrogen. Think compost and other forms of organic fertilizers.

Root Rot

Root Rot
Image by Reddit

How to Fix: Improve soil drainage, avoid overwatering, and repot basil in fresh, well-draining soil.

Root rot is another water-related issue that should be taken seriously as this not only causes yellowing leaves but can also kill untreated plants. Basil roots can rot if they’re always in waterlogged soil. 

This encourages harmful fungi that attack the roots, making them decay. As a result, the roots can’t absorb water and nutrients properly. 

Poor aeration and drainage harm the plant’s overall health. Signs of root rot are yellow leaves, wilting, and a bad smell from the soil.

Solution: Improve soil drainage, avoid overwatering, and repot basil in fresh, well-draining soil.

FactorInformation
DifficultyModerate ●●○○○
SpeedSlow to moderate recovery may take weeks as the plant needs time to regrow healthy roots and establish in the new soil.
Materials NeededDisinfected pruning shears, fresh well-draining soil, new pot (if repotting), fungicide, watering can.

When the culprit for yellowing basil leaves is root rot, you need to act immediately. Remove the affected basil plant from its pot or soil carefully. 

Trim away any dark, mushy roots, ensuring you use disinfected tools to prevent the spread of disease. Allow the roots to dry in the open air for a short period. 

Repot the basil in fresh, well-draining soil, ensuring the new container or planting area has proper drainage holes. Avoid overwatering in the future and adjust the watering schedule to keep the soil consistently moist but not waterlogged. 

Applying a fungicide and following the product instructions can also help control the spread of the root rot fungus.

Pests

Pests
Image by Click & Grow Ask a Gardener

How to Fix: Use neem oil or insecticidal soap and remove affected leaves as needed.

Yellow basil leaves can result from pest presence, like aphids or spider mites. Aphids, small sap-feeding insects, and spider mites, tiny arachnids, both extract juices from the leaves. 

These pests cause discoloration, distortion, and overall decline in basil plants. Aphids often gather beneath leaves, leaving behind a sticky substance called honeydew. 

Spider mites produce fine webbing and stippling patterns on the leaves. Left alone, these pests can wreak havoc on your plant and spread to neighboring plants.

Solution: Use neem oil or insecticidal soap and remove affected leaves as needed.

FactorInformation
DifficultyModerate ●●○○○
SpeedModerate improvement can be seen within a week, but continued monitoring is essential.
Materials NeededInsecticidal soap or neem oil, spray bottle, pruning shears, water source for rinsing (if using water spray).

Controlling pest infestations is not a one-step approach. You’ll have to physically remove the pests first by spraying the basil plant with a strong stream of water. 

This helps dislodge aphids and spider mites from the leaves. Combat these pests with insecticidal soap or neem oil, eco-friendly choices. 

Follow the product instructions to make the mix, then spray it on problem areas, covering well. Apply as necessary, especially after rain. 

Trim and discard heavily-infested leaves to stop pests from spreading. Don’t consume treated leaves, as they may contain residues from neem or insecticidal soap.

Diseases

Diseases
Image by Positive Bloom

How to Fix: Ensure good air circulation around the plant. Use fungicides if the issue persists.

Yellowing basil leaves can result from diseases like Fusarium Wilt and Downy Mildew. Fusarium Wilt is a soil-borne fungus that hampers water flow in the plant, causing wilting, yellowing, and eventual death. 

Downy Mildew is a foliar disease caused by a water mold and shows up as yellow spots on leaves’ upper side and fuzzy, purplish growth underneath. These diseases spread through contaminated soil, water, or infected plant material.

Solution: Ensure good air circulation around the plant. Use fungicides if the issue persists.

An ounce of prevention is worth a pound of cure – and this is best when guarding your basil plants against diseases. There are a lot of preventative actions you can take. 

Give your basil plants space for good air circulation. Water the soil, not the leaves, to keep them dry. 

Also, it’s wise to choose disease-resistant basil types. If you see signs of Fusarium Wilt or Downy Mildew, remove and destroy affected leaves. 

Apply a basil disease fungicide, following the instructions. Don’t handle wet basil plants to avoid spreading diseases.

Extreme Temperatures

Extreme Temperatures
Image by – Kitchen Herbography

How to Fix: Protect basil from extreme cold or heat. 

Basil is a warm-season herb that thrives in moderate temperatures. When exposed to excessively high temperatures, the plant may experience heat stress, leading to yellowing, wilting, and a general decline in health. 

On the other hand, exposure to frost or chilly conditions can also cause basil leaves to turn yellow and suffer from cold stress. 

Solution: Protect basil from extreme cold or heat. 

FactorInformation
DifficultyLow to Moderate ●●○○○
SpeedModerate improvement may take a few days to a week, depending on the severity of stress and the plant’s ability to recover.
Materials NeededShade cloth or structures for shade, frost cloth (for cold protection), movable containers (for potted basil), weather monitoring tools (optional).

In hot weather, protect your basil from the hottest parts of the day, especially in the afternoon. Position it to get morning sunlight but avoid intense afternoon sun. 

If it’s cold, bring potted basil inside during frosty nights or cover outdoor plants with frost cloth. For potted basil, placing it against a sheltered wall can add extra warmth.

Inadequate Sunlight

Inadequate Sunlight
Image by Rural Sprout

How to Fix: Place the basil plant in a location with at least 6 to 8 hours of direct sunlight per day.

Basil thrives in sunlight, needing at least 6 to 8 hours daily for best growth. Without sufficient sunlight, stress sets in, reducing chlorophyll production and causing yellow leaves. 

Not enough sunlight also leads to leggy growth, pale leaves, and a weakened appearance. This often happens when growing basil indoors or in shaded spots, reducing effective photosynthesis.

Solution: Place the basil plant in a location with at least 6 to 8 hours of direct sunlight per day.

FactorInformation
DifficultyLow to Moderate ●●○○○
SpeedModerate improvement may take a few weeks as the plant adjusts to its new light conditions.
Materials NeededSunlit location, artificial grow lights (if necessary), pruning shears (optional).

Choose a spot with 6 to 8 hours of direct sunlight daily. For indoor basil, put it close to a south-facing window for sufficient sunlight. 

If natural light is lacking, use grow lights. Rotate potted basil often for equal light exposure. 

Old Age of Leaves

Old Age of Leaves
Image by luv2garden.com

How to Fix: Regularly prune older leaves to encourage the growth of new, healthy foliage.

As basil matures, its lower leaves naturally yellow and eventually fall off. This is a normal part of the growth cycle, and it doesn’t necessarily indicate a problem with the plant’s health. 

We recommend that you do a regular pruning of these older leaves to maintain the plant’s appearance as well as to encourage the growth of new, healthy foliage.

Solution: Regularly prune older leaves to encourage the growth of new, healthy foliage.

FactorInformation
DifficultyEasy ●○○○○
SpeedFast improvement is noticeable shortly after pruning, promoting new growth.
Materials NeededClean and sharp pruning shears. Regular monitoring of the plant’s overall condition.

As basil plants grow, trim off lower, older yellow leaves using sharp pruning shears. Snip them at the stem base to encourage bushier growth. 

Don’t cut more than a third of the plant at once to prevent stress. Regular pruning improves air circulation. 

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