Why Basil Leaves Turn Brown And How To Fix It

Basil is relatively easy to grow at home, but as with many herbs, the leaves are tender and the plant itself needs to be handled with care to prevent the delicate basil leaves from falling foul of the many issues that can affect this plant.

You’re here because you’ve spotted a few Basil leaves turning brown, and quite rightly, you want to know what’s going on with the plant. The good news is that if you act now you can identify the cause, then you can take the steps I recommend to nurse your plant back to full health.

Why Does My Basil Plant Have Brown Leaves?

Basil, like most plants, has five basic requirements for growth – water, light, warmth, nutrients, and oxygen. A deficiency or excess of any of these can cause damage to the plant cell structure or weaken it to the point where it is prone to fungal, bacterial, or pest attacks.

Not enough water and the leaves will dry out and feel crispy on the tips, too much water and the leaves will soften and turn brown, or fungal infection will cause rotting to take place and the leaves will drop. So let’s look at each of these and talk about their specific symptoms and remedies.

5 Reasons Basil Leaves Turn Brown

To quickly identify which of these problems is at play you will need to establish how the discolored leaves feel to pinpoint the exact cause and therefore the best way to fix it.

1. Basil Leaves Turning Brown & Falling Off

Basil plants can be susceptible to fungal diseases which thrive in humid and damp conditions, typically simulated when soil is over-watered. If a disease takes hold, it will often result in basil leaves turning brown, stunted growth, and eventual leaf drop. Some of the more common diseases in basil include downy mildew, fusarium wilt, and cercospora leaf spot.

Downy mildew is a type of fungal disease that can affect basil plants. Symptoms include yellow patches on the top of the leaves, and dark spots on the underside of the leaves, leading to wilting and turning brown. This usually occurs during periods of warmth, when humid conditions are present. To prevent downy mildew practice good hygiene by removing infected leaves, and avoiding over-watering or overcrowding.

Use a fungicidal treatment for large infections, or pick off any infected leaves and dispose of them.

Basil leaves are affected with downy mildew - Basil Leaves Turn Brown
Basil leaves showing symptoms of downy mildew

Fusarium wilt is a soil-borne fungus that causes the water-carrying vessels in the basil to become blocked causing the plant to wilt and die. Leaves will turn yellow, then brown then eventually drop off. You will also notice brown streaks on the back.

Damping off is also soil-borne but tends to impact much younger plants. If you notice your seedling plant rotting from the roots and the leaves turning brown and dropping, then it could be this disease.

Cercospora leaf spot is a fungal disease that infects basil plants and causes circular dark brown spots on the leaves.

How To Fix

All of these diseases can be treated by removing any impacted leaves and then treating the plant with a fungicide containing potassium bicarbonate. 

In the case of fusarium wilt or ‘damping off’, the best solution is to pull the basil up and dispose of it in a rubbish bin rather than a compost pile as they could all spread through your soil and cause the compost to become contaminated and smell.

Prevention is always better than cure, so avoid overwatering, as damp environments encourage fungal growth. Always water directly into the soil or from beneath the pot, never water directly onto the basil leaves. Be sure to allow sufficient space between plants to allow for suitable airflow, a few inches will do. 

2. Brown Withered Leaves After Re-Potting

If your basil has started to show brown leaves and is withering too it may simply be due to shock and stress. 

Basil grows quickly and if it is in a pot this can lead to it outgrowing it rapidly. It can react badly to being handled too much so if you have recently re-potted this could be the reason. 

How To Fix

Basil transplants should be given time to adjust to their new surroundings without being overwatered or experiencing any significant changes in temperature or habitat. 

Once you have re-potted, it is wise to then leave the plant in the same position, so it does not also need to adapt to any other new elements. I also recommend that you avoid switching the pots too frequently because doing so can cause the plant to die.

3. Soft Brown Leaves From Overwatering

Too much water is a very common problem for basil plants. Overwatering will cause the roots to rot and the leaves to turn yellow and then brown and feel mushy. This is because excess water will fill up the airspaces in the soil, depriving the roots of oxygen. Without oxygen, the roots will die and adversely affect the plant’s ability to take up water.

Overwatering happens most often with indoor basil because there is less evaporation of moisture indoors. The soil needs to be moist, but not soggy. This can be a particular problem if your basil is planted in a pot without a drainage hole.

How to Fix

If you suspect you may have over-watered your basil, the first place to check is the roots. If they are soft, mushy, and brown in colour, then they are rotting.

If the damage is minimal, you can save the plant by replanting it in new soil and only watering it when the soil is dry to the touch. This should soon remedy itself and you will be back to green leaves. 

However, if the roots have entirely rotted, then the plant cannot be salvaged.

Often soil that appears dry on the surface is still damp underneath making overwatering very easy to happen. 

To prevent it from happening again, before watering your basil, push your finger around 1 inch into the soil to check the roots are not still damp. If they are, just skip watering that day. 

4. Brown and Crispy Basil Leaves

The number one cause of brown basil leaves with crispy edges is under watering. If you are not watering enough, the basil could begin to dry out and if the problem persists it will begin to die. 

Water is also crucial for the plant to absorb adequate nutrients so an inconsistent watering schedule will also impact this.

Underwatered basil is usually bitter and produces a pungent smell rather than aromatic. 

How To Fix It

Make sure you are watering your basil on a regular schedule. In temperate conditions, basil only really needs to be watered well once per week. This will allow your herb to have a constant intake of water on a consistent basis, keeping it happy, healthy, and green. 

If you identify this to be the issue and the whole plant has not started to die, you can prune off the underwatered crispy brown leaves, then get back to a consistent watering schedule with an initial feed to allow the plant to recover. Your reward will soon be green leaves once again. 

5. Low Light Leads to Yellow and Brown Leaves

Basil thrives in sunny weather and requires 6 – 8 hours of sunlight every day. It is an essential part of photosynthesis that helps basil store energy to produce more leaves and grow. So, without enough light, they may start to wilt and turn yellow and brown. 

However, too much sunlight can harm plants too and more than 10 hours of full sun can lead to brown scorch marks on your leaves. 

How to fix

Firstly, check your basil is not under a tree or another source of shade that might block it from full sunlight and if yes, consider moving it. 

However, if your local climate just does not provide the required amount of sunlight on a regular basis then you should probably consider growing your basil indoors and using a windowsill that faces south or potentially even an indoor grow light.

If on the flipside your basil plant is getting too much sunlight and heat, a shade cloth is a good investment.

Planting your basil in a pot will help you to move it around to maximise or minimize the heat and sunlight it is exposed to.

If you believe sunlight has been the cause for some discoloured leaves, simply prune away any yellow or brown sections then remedy the cause to soon be rewarded with dark green leaves once again.   

Other Causes Of Brown Basil Leaves 

Basil prefers slightly acidic soil that is not too rich in organic matter.

If you notice brown leaves and are struggling to identify any of the above issues then it could be a soil issue. Often brown leaves indicate that the soil is too acidic which can lead to scorching throughout the plant.

Browning leaves could also be the result of chemical fertilizers. Use a feed that is specifically designed for fertilizing herbs as they tend to be gentler with a lower NPK ratio.

For a more natural and gentle remedy, try sprinkling old tea leaves around the plant and soil, twice every growing season. 

Verdict: Basil Leaves Turning Brown

Basil leaves are very delicate so if they start to brown it is an early indicator that the plant is under stress. 

Quickly identifying the cause will allow you to resolve the issue (unless it has been caused by disease in which case it should be disposed of) and soon you will be rewarded with fragrant and green leaves once again!  

FAQ Brown Leaves on Basil Plant

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.