Basil is one of the most popular herbs found in gardens, whether outdoors or in kitchen containers. Due to its low-maintenance care, home chefs often find creative ways to add basil to their dishes. Even those not using it for cooking often grow it for its pleasant aroma.
While easy to grow, basil is not free from issues. One of the most common problems gardeners face is their basil leaves turning yellow. This can be caused by a variety of issues, but, thankfully, most are easy to fix. Let’s look at some of the causes of yellowing basil leaves, and what you can do to restore your plant to peak health.
Underwatering
A lot of inexperienced homeowners can find their basil leaves turning yellow due to underwatering. Sometimes, it’s due to forgetfulness, and sometimes, it’s just because you’re giving the herb too little water.
Signs of Underwatering
When the leaves are yellow and crispy, it’s a sure sign of underwatering. This means that the leaves have been dehydrated for some time. As a result, the plant selectively cuts off some leaves to survive and conserve what little water it has. This leads to yellow, brittle leaves that will crumble if touched.
How to Fix Underwatering
Create a watering schedule that is more frequent and regular. This applies not only to your basil plant but to all plants as well. By providing your basil plants with regular and adequate water, you ensure that they don’t become thirsty. You should also be wary of going too far in the other direction and overwatering, which we’ll touch on next.
Overwatering
When you water your plants too much, they can begin to show signs of stress. One of these signs is the presence of yellow leaves. Basil plants thrive in well-draining soil that is consistently moist, but not soaked. If the roots are kept too wet all the time, they develop root rot and the leaves can turn yellow.
Signs of Overwatering
At first, it may seem difficult to tell the signs of overwatering from underwatering. If underwatered plants have dry crispy yellow leaves, overwatered plants often have soft soggy yellow leaves. Additionally, potted plants tend to experience root rot more often than those grown in the ground.
How to Fix Overwatering
There are several ways you can fix this issue. Let’s go over each.
If wet, compacted soil is the cause, then you have to ensure that the soil drains water better. Add soil amendments, such as compost, garden sand, perlite, vermiculite, or a combination of the mentioned amendments. You can also repot your plant with fresh soil to help increase its drainability.
If the cause is due to a basil plant being placed in a pot having little or clogged drainage holes, then you need to do one of two things: add more drainage holes or get a new pot with a lot of drainage holes. Repot the plant in well-draining soil and your basil should come out healthier.
If the reason is due to excess watering, then you need to cut down on the frequency. Allow the top inch of the soil to dry out slightly before watering your basil plant. Once you water your basil plant correctly, you should see it come back with bigger and greener leaves.
Once the roots begin to rot it is often too late to save the plant, so be careful not to overwater and check regularly for signs of stress.
Inadequate Light
Basil leaves can also turn yellow when there isn’t enough sunlight. Basil plants not receiving adequate light can develop yellow leaves as the plant tries to conserve energy. As basil plants thrive in full sunlight you have to ensure that they are consistently getting enough sunlight. This is often an issue during the winter when the sun is less intense in more temperate climates.
Signs of Inadequate Light
Yellow basil leaves are clear signs. This is especially clear when the yellow leaves are located on the far side of the light source. This can be difficult to differentiate from lack of water, so use your best judgment to determine if light or water is the issue.
How to Fix Inadequate Light
Place your basil plants in an area that receives at least six hours of sunlight. Indoors, a south or easterly-facing window is your best bet to get your plant enough light.
You can also supplement your indoor lighting with plant grow lights. These are readily available in many hardware stores and nurseries. Select the one that suits your needs, plug it in, and watch your basil regain its health.
Low Temperatures
Basil plants are tender herbs that react negatively to cold weather. If you live in an area that experiences low temperatures, it’s best to keep your basil plants indoors. They should also be placed away from drafty areas like windows or poorly insulated exterior walls.
Signs of Low Temperatures
Aside from yellowing leaves, your basil plant will also likely have one or more of the following symptoms: stunted growth, wilting, blackened stems, or poor flavor. To validate this cause, determine if your basil plant is exposed to low temperatures or cold drafts. If you can feel it, then your plant can too.
How to Fix Low Temperatures
Basil plants are herbs that thrive in warmer temperatures. Keep your basil plants indoors during the winter, especially before the first signs of frost set in. Keep the basil plant in areas with temperatures that range from 50 F to 80 F.
If your plant is near a drafty area then move it to one with a more consistent temperature or fix the draft. If this is the case, you may see the above symptoms more prominently on the side of the plant facing the draft.
Overcrowding
Basil is a quick grower and under ideal conditions will experience rather strong growth. This can result in a bushy basil plant that eventually has yellowing leaves due to overcrowding. It can also be the result of planting too many basil plants in close proximity to each other.
Signs of Overcrowding
This can be a tricky one to determine, but look for plants that are visually overcrowded. In general, you want to leave about 10-12 inches between each basil plant. If you’re planting them closer than this then overcrowding might be the issue.
This is not the most common of issues though. My advice is to rule out water and sunlight first as they are the more likely culprits. If neither of those are the issue, then you can consider overcrowding.
How to Fix Overcrowding
There are two ways to fix overcrowded basil plants. Let’s take a look at them both.
If your basil plant is producing yellow leaves due to too much leaf growth, the best thing to do is prune it. This will encourage your plant to become bushier by producing new leaves. At the same time, you have more leaves to add flavor to your dishes.
If the reason is having more than one plant in one container, you can divide them. This will give you two potted basil plants. However, if this is not an option, repot the plants in a bigger container.
Pests
Basil is normally resistant to most pests. In fact, it is often used to deter several pests by planting it along with other plants that are susceptible to pests. However, there will be occasions when basil plants are visited and infested by pests.
Signs of Pests
There are several signs that your yellowed basil leaves are the result of pests. Note that this is more likely to affect plants grown outdoors, but occasionally indoor gardens will experience pests as well.
The physical presence of unwanted insects is the most evident sign. Common basil pests are aphids, spider mites, whiteflies, thrips, and mealybugs.
If you notice small round holes in the leaves, it is most likely due to pests. The usual suspects are slugs, snails, and caterpillars.
Aside from turning yellow, basil leaves that are brown or black can mean the presence of pests. These include spider mites, aphids, and whiteflies.
If there are sticky residues on the leaves of healthy or yellow leaves, then this is likely the work of pests. Aphids and whiteflies produce a sugar substance that attracts other pests, damaging the plant even more.
Spider mites cause webbing to appear on leaves. These webs are fine and silk-like but will cause the leaves to turn yellow and eventually die.
Another tip is to always check the undersides of leaves when inspecting your plants. Many types of pests will hide on the undersides of leaves which makes them difficult to see if you’re not actively looking for them there.
How To Fix Pest Issues
How you deal with pests largely depends on the type of pest and how large of an infestation there is. Small amounts can often be brushed off or blasted with water to remove them. Larger infestations though can require the use of more sophisticated pest control techniques. For this reason, it’s a good habit to check on your plants every few days to help catch any pest issues early.
We also have a full article on natural pest control techniques you can use in your garden. If you’re dealing with pests then give it a quick read for some helpful tips to get rid of them.
Fungal Diseases
Just like us plants are susceptible to a variety of diseases, and basil is, of course, no exception. These diseases can be caused by a variety of issues such as pests, improper care, or the growing environment of the plant.
Signs of Diseases
There are a wide variety of diseases and many present different symptoms making it difficult to give general advice. In general, look for any issues present in addition to the yellowing leaves. Many plant diseases leave other traces such as blackened/browning stems and leaves, stunted growth, and even physical mildew. Below, you’ll find a couple of the common culprits but this list is by no means exhaustive.
Fusarium wilt is a common fungal disease that causes yellowing basil leaves. The stems usually turn brown or black, spreading throughout the whole plant eventually. Left untreated, basil plants can end up with stunted growth, wilting leaves, and even plant death.
Another common basil disease is downy mildew. Aside from yellow leaves, brown leaves also become a regular occurrence. Infected leaves tend to exhibit grayish-white downy growth on the undersides. Downy mildew can cause basil plants to have stunted growth and a decline in overall health.
How to Fix Fungal Diseases
Luckily, fungal diseases can be fixed by using the appropriate treatments. We’ll list several to help you determine the one that suits your needs. This list is not exhaustive though, so make sure to research the specifics to find appropriate treatment.
In many cases, the easiest way to stop the spread of disease is to isolate the affected plant(s). This can be the entire plant, or, for localized issues, the parts of the plant affected. Simply pruning off diseased pieces can help prevent the spread to the rest of your plant.
Neem oil is a natural fungicide that is effective against various fungal diseases. By disrupting the life cycle of the fungus, neem oil solutions prevent them from reproducing and spreading.
Disease Prevention
Now that we’ve gone through the fixes, let’s look at how to prevent fungal diseases. After all, an ounce of prevention is worth a pound of cure.
Practice good plant hygiene by keeping the area around your plants clean and free from debris. Avoid overwatering, and provide good air circulation around your plants. Just by these steps alone, you help ensure the health of your plants and minimize the risk of fungal diseases.
You should also make sure that your plant is getting adequate nutrients and care. Plants weak due to neglect are much more likely to succumb to disease than healthy plants.
Lack of Nutrients
Yellow basil leaves can also be due to a lack of nutrition. Sometimes, this is the result of root rot since the plant is unable to absorb nutrients due to damaged roots. Other times, it is due to poor soil drainage or soil that has been depleted of nutrients.
Signs of Lack of Nutrients
Aside from yellow basil leaves, a plant that lacks nutrients can have leggy growth and sparse foliage. Overall, a basil plant lacking nutrients will exhibit poor health and even stunted growth.
How to Fix Lack of Nutrients
The best way to boost soil nutrients is to add amendments. Compost is the most popular approach since it is completely organic, full of nutrients, and enhances the texture of the soil.
Compost releases essential nutrients slowly over time. As a result, your basil plant will end up healthier as it continues to grow.
Other ways to add nutrients to the soil include slow-release fertilizers and inorganic fertilizers. When applying these, follow the instructions on the label to ensure the right amount is used.
Lastly, if growing in a container, it’s a good idea to swap out the soil every few years. This not only adds fresh nutrients but helps combat the natural compaction that soil will go through. Given enough time, this compaction can lead to drainage issues.
Age
Finally, it’s important to note that the yellowing of older leaves is a natural process in basil plants. As the plant grows and matures, the older leaves may turn yellow and drop off. This is normal and nothing to worry about as long as the newer leaves remain green and healthy.
While there are no fixes for this, you are encouraged to trim or harvest basil leaves regularly. This will encourage your plant to produce more leaves and lead to a bushier plant in the process.
You can also regularly take cuttings of your basil plant and plant them. This helps you extend your basil’s life as you’ll have fresh plants to take over for the aging parent.
Basil Leaves Turning Yellow
Yellowing basil leaves can have a variety of causes but is generally easy to fix. The key is to catch the issue early. The sooner you catch and deal with the root cause the better chance you have of saving your basil plant.
