Basil is one of the best, most versatile fresh herbs to grow in your home garden or kitchen. It’s definitely one of my personal favorites!

Most of the time, it’s an easy-to-grow herb. But if you have basil leaves turning yellow on you, there’s a problem somewhere. These are the most common ones:

1. Watering problems
2. Nutrient problems
3. Lack of sunlight
4. Pests
5. Diseases

Let’s figure out why your basil leaves are turning yellow and what you can do about it!

1. Too Much or Not Enough Water

Like most other plants and herbs, over or under-watering is often the cause of yellowing leaves on basil plants. 

Too little water, and your basil will sacrifice the old leaves to conserve water for the new growth. Hence, these older leaves can turn yellow and die. 

If your basil is overwatered, the roots can’t take in oxygen from the soil. So you’ll see leaves become unhealthy and discolored. 

Solution: Adjust Your Watering Routine

Go and physically feel your soil. Is it soggy or dry? Is there standing water or is the soil a solid, rock-hard mass? These are two extremes, but they’re both fixable as long as the damage isn’t too severe. 

If the soil is waterlogged, stop all watering for at least a few days. Also, make sure the pot (or garden) has good drainage to prevent puddling. After a few days, stick your fingertip in the soil. If the top 2 to 3 inches of soil still feel damp, don’t water yet.

When the soil does start to feel dry, it’s time to water. Give just enough water to soak the soil without leaving any standing pools. 

On the other hand, if the soil is dried out, give water immediately. However, be careful not to flood your plant. You’re much better off to give several smaller doses of water over the course of a few hours than you are to give one big gulp at once. 

Going forward, you can prevent problems by meeting your basil’s moisture needs- not too much, not too little. I’ve dedicated an entire post to watering basil the right way, so stop by to learn more details.

2. Lack of Nutrients

Basil isn’t too picky when it comes to soil quality, and it can do very well even in poor soil.

But like other plants, it needs the proper balance of nutrients to grow and thrive. 

Nitrogen, potassium and other nutrients need to be present in the soil for basil to grow and thrive. 

As the graphic above shows, a lack of several nutrients could be to blame for yellow leaves. 

But low potassium is the most common leaf-yellowing issue in basil plants.

Solution: Add Nutrients to Your Soil

Add nutrient-rich organic matter to your soil. Compost or well-rotted manure are two of the best options. 

You can order compost online from Amazon. But it’s pretty expensive, and you’re probably much better off to check at your local nursery or home improvement store. 

Another option is to use a targeted fertilizer. I like this organic formula on Amazon since it’s ideal for veggies and herbs.

Follow feeding instructions to increase healthy growth and prevent those basil leaves from turning yellow!

3. Not Enough Sunlight

Yellowing leaves on a basil plant could also mean it isn’t getting enough sunlight. 

Sunshine is a foundational component for healthy chlorophyll production, which gives your plants that healthy green color. 

Not enough sunlight = less green and more yellow. 

Solution: Increase Light Exposure

Outdoor basil likes bright sunlight for at least six to eight hours daily. Grown indoors, that light requirement shoots up to 12 hours daily, especially in the winter. 

So let the sun shine in! If you can, clear any hedges or tree limbs that are blocking the sun’s rays to your basil plants. 

For container-grown basil, it’s a little easier: Move your plants to a sunnier spot on your porch or in your kitchen.

If you’ve got an indoor basil plant, place it in the sunniest window you can, typically a south-facing one. If you don’t have that available, consider using a grow light.

4. Pest Infestations

Basil can turn yellow when there’s a problem with pests.

This doesn’t happen often, but aphids, caterpillars, and root-knot nematodes are the most common pests that will try feeding on your basil plants. 

Here’s what they look like:

It’s always best to try and prevent infestations.

But as any gardener knows, that doesn’t always work out.

Solution: Get Rid of Pests

For aphids, apply an organic insecticidal soap.

Be sure to avoid using it on hot days and when the sun is shining directly on basil leaves to prevent scorching. If you’re in the midst of a hot, dry spell of weather, treat your plants early in the morning before the sun’s rays get too strong. 

Caterpillars can usually be picked off by hand. If you have backyard chickens, these caterpillars make a great treat!

Or consider applying some Bacillus thuringiensis (Bt) to get rid of them. However, timing is critical with Bt – so follow the package directions carefully. 

Root-knot nematodes are small worms that live in the soil. Some species can form parasitic growths on your basil plant’s roots, weakening it to the point where it can’t support healthy foliage.

If you want to know more about nematodes, stop by this helpful article from Oregon State University.

If you find bulbous growths on your basil plant’s root when you pull it from the ground, you may have root-knot nematodes. Unfortunately, there isn’t much you can do to rid your soil of them.

So your best bet is to find another spot in your garden or consider a container planting with some good quality potting soil.

5. Diseases

Yellowing leaves on basil plants may also indicate a fungal disease. 

There are a few different types of fungal diseases known to affect basil, but the most common is downy mildew. 

It spreads fast and will cause fuzzy gray and brown patches on your basil leaves, eventually progressing to a yellow color. 

Solution: Clear Up Diseases or Remove Infected Plants

Clip off any leaves that have been affected by downy mildew, being careful not to brush any unaffected leaves or shake any of the mildew off onto the soil.

But if your basil plant looks like it has a lot of downy mildew, it’s probably best to remove the plant carefully and bag it up to prevent the spread of the fungus.

Prevent overwatering by watering less often and ensuring proper drainage. Fungus loves moisture!

Final Thoughts

According to WebMD, basil boasts several health benefits including antioxidant properties, regulation of blood sugar, and alleviation of depression and anxiety. 

The smell when harvesting the leaves just can’t be beat (plus it wards off wasps!). It’s an easygoing herb with very few demands and a great number of culinary uses. 

So don’t let yellow leaves stand in your way to enjoying this wonderful, versatile herb!

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