Generally speaking, basil is a pretty easy herb to grow, but there are some things that can go wrong, including some things you can do wrong and some pests and diseases that can lead to problems.
In this post, I list 12 common problems people often have to deal with when growing basil and explain how to identify them as early as possible and what to do about them to keep your plants healthy. If you have a specific problem with your basil, find it on the list below to see how to take care of it.
1. Root Rot
As the name implies, Root rot is when a plant’s roots begin to rot. It happens when the plant gets too much water for too long. When a plant’s roots rot, they can no longer obtain water and nutrients and keep the plant stable in the ground, so if the problem persists for too long, the plant dies. Root rot is a pretty common problem with basil because it is a relatively small and fragile plant, especially when it is young.
How to identify root rot
The earliest signs of a basil plant suffering from root rot are yellowing leaves, wilting, and stunted growth. After some time, the plant will begin to drop its leaves, and a smell of mold will start to come from the soil and the roots.
What to do about root rot
The best way to deal with severe root rot is to transplant the plant to a large pot with new soil. Only water the plant when the top of the soil is dry and water it by pouring water into the plate underneath the pot if possible.
Root rot is almost always caused by incorrect watering. I have a guide for watering basil here, so you can avoid it.
2. Mold on the Soil
If a basil plant has been getting too much water for an extended period of time, mold can sometimes begin to appear on the top of the soil. Like root rot, mold is caused by overwatering, and once it spreads enough, it can be deadly for the plant.
How to identify mold on the soil
The first thing you will see is usually small white patches of mold appearing in a few places around the top of the soil. If you don’t take care of it and keep overwatering your plant, it will spread quickly.
What to do about mold on the soil
The best way to remove mold from the top of the soil is to simply use a spoon or similar and gently scrape it off. If there is a lot of mold on the soil, it is best to transplant the plant to another pot with new soil. Avoid overwatering by only watering when the top of the soil is dry and ideally from the bottom.
I have another article where I dive deeper into what to do when you see mold on your basil’s soil. You can find the article on this link.
A plant becomes rootbound when its root system has grown so much that it takes up all the room in the pot or container it is in. It usually happens to basil plants that grow in too small containers, and when it happens, the plant will grow much slower.
How to find out if your basil plant is rootbound
The first sign that a basil plant has become rootbound is that it will grow slower and slower and eventually stop. It is much more likely to happen to basil plants that are in small pots than in large pots or in the ground.
What to do when your basil plant is rootbound
The best thing you can do to save a rootbound basil plant is to transplant it to a bigger pot or into the ground where it has enough room for the root system to grow. I have a guide for you here.
4. Leaves Turning Yellow or Brown
There are several reasons why basil leaves begin to turn yellow or brown like on my Lettuce Leaf Basil in this photo. The most common reason is overwatering, but overexposure to sunlight will also cause the leaves to turn yellow or brown.
How to identify basil leaves turning yellow or brown early
Luckily this one is super easy to identify early since it happens directly on the leaves, so just keep an eye on the leaves to see if they begin to turn yellow or brown. Don’t get fooled by the lower leaves changing color when the plant is a few months old, since that is completely normal, but if the top leaves are changing color, there is some kind of issue.
What to do when basil leaves are turning yellow or brown
When basil leaves turn yellow or brown, you must make sure the plant is not being overwatered or overexposed to sunlight. It should get 6-8 hours of sunlight per day and only be watered when the top of the soil is dry to touch. Watering from the bottom further reduces the risk of overwatering.
5. Leaves Not Growing
There are several reasons why the leaves on your basil plant are not getting big. The most common reasons are lack of sunlight, water, or nutrients, or not enough growing space. Certain basil varieties such as Minette basil and spicy globe basil only ever grow tiny leaves about ½-1 inch (about 1-2.5 cm) long.
How to tell if basil leaves are not growing enough
Basil plants should have leaves that are at least about 1-2 inches long after growing for 1-2 months, so if the leaves are much smaller than that, you might have a problem. Just keep in mind that certain basil varieties, such as Minette basil and spicy globe basil, never grow big leaves.
What to do when your basil’s leaves are not growing enough
Make sure the plant is getting 6-8 hours of direct sunlight per day and is growing in nutrient-rich, well-drained soil. Potted basil should be in pots that are at least 8 inches (20 cm) in height and diameter, and basil in the ground should have at least 12 inches (30 cm) of space around it. I dive deeper into the issue of basil leaves not growing on this link.
6. Powdery Mildew
Powdery mildew is a white, mold-like substance that can appear on the leaves of basil plants.
How to identify powdery mildew early
Powdery mildew first appears as small white patches around the leaves. It usually begins to appear on the lower leaves and then spreads to other nearby leaves as it moves up towards the top of the plant.
What to do about powdery mildew
Remove any infected leaves as soon as possible. If you are unsure about some leaves, remove them too to reduce the risk of further infection. Powdery mildew can sometimes be treated by mixing one tablespoon of baking soda, a half tablespoon of liquid soap, and a gallon (3.8 liters) of water and spraying it on the plant.
7. Downy Mildew
Downy mildew on basil comes from a fungus-like organism called Peronospora belbahrii. It can be introduced into a garden by wind-borne spores or by infected seeds or transplants (source).
How to identify downy mildew early
Downy mildew first appears as small yellow or light green spots around the leaves on basil and can quickly spread to the whole plant. Eventually, the plant will turn brown and die.
What to do about downy mildew
The best way to deal with downy mildew is to stop it before it spreads too much. Remove any potentially affected leaves as early as possible before it spreads.
Aphids look like tiny white insects, and they will usually appear in pretty large numbers and crawl all over your basil plant and its leaves.
How to identify aphids
Aphids are tiny, so keep a close eye on the plant. They are easy to overlook until there are a lot of them, at which point they are harder to deal with than if you caught it early.
What to do about aphids
Spray the plant with neem oil. Neem oil is a natural oil that essentially coats the plant and makes it unattractive to aphids. A long-term solution is to grow plants such as asparagus that attract ladybugs and other beneficial insects to your garden that will eat the aphids.
Whiteflies are essentially just some tiny, white insects (i know, not a very creative name) that climb all over your basil. They can multiply quickly, so keep an eye out for them.
How to identify whiteflies
Whiteflies are small but not so hard to see when they crawl all over a basil plant, so just keep an eye on your plant to make sure there are none of them.
What to do about whiteflies
Spray your plant with neem oil to create a coating layer that makes the plant unattractive to whiteflies. You can also plant asparagus and other plants that will attract helpful insects, such as ladybugs that help keep the whiteflies away.
10. Flea Beetles
Flea beetles are small, black beetles that can move quickly around a basil plant and will feast on leaves. At first, they will just make small holes in some leaves, but if the problem spreads too much, the beetles will eat entire leaves and potentially whole parts of the plant.
How to identify flea beetles
Flea beetles are tiny, but their black color makes them stand out from the green leaves on basil, so they are pretty easy to see. Just keep an eye out for them.
What to do about flea beetles
Dust your basil plant with plain talcum powder to get rid of flea beetles. It is also a good idea to remove any unnecessary weeds around your basil plant to reduce the number of food sources for the beetles.
11. Spider Mites
Spider mites look like tiny red spider-like insects. They are super hard to notice if you are not looking specifically for them because they are so small, but luckily their red color stands out from the green basil leaves, which makes it a bit easier.
How to identify spider mites
Look closely at your basil plant once in a while. Spider mites are tiny and can be hard to see.
What to do about spider mites
Fill a spray bottle with water, add a few drops of essential oils from rosemary, and spray the solution all over your plant. A longer-term solution to getting rid of spider mites on basil is with ladybugs, lacewings, and other beneficial insects that eat them.
12. Japanese Beetles
Japanese beetles are about ½ inch (1.25 cm) long and have a shiny, metallic green and brown color. They feed on green leaves and are especially happy to eat basil.
How to identify Japanese beetles
Japanese beetles are large enough to easily see with the naked eye. They are about ½ inch (1.25 cm) long and have a shiny brown and green color.
What to do about Japanese beetles
Spray your basil plant thoroughly with neem oil once a week until the Japanese beetles are gone. Another strategy is to use a plant cover to create a physical barrier for the beetles, but make sure the plants have room to grow and still get sunlight.
Read My Complete Guide to Growing and Caring for Basil
I have written a thorough guide where I cover all parts of growing your own basil including choosing a variety, sowing the seeds, the best growing conditions, pruning, propagation, harvesting, storing, solving various problems, and a lot more. You can find the article on this link.