The basil plant is popular because it has a sweet-spicy flavor. From time to time, you may encounter a challenge with your basil leaves turning yellow. The most common complaints are overwatering, cool temperatures, or diseases like basil downy mildew. Keep reading to learn more about why basil leaves turn yellow and what you can do about it.
How are your basil leaves turning yellow?
The best way to prevent yellow leaves is by providing ideal growing conditions. Even the most attentive gardeners may occasionally find themselves dealing with yellowing leaves. Before you panic, take a look at the plant. A leaf that is yellow is not usually a symptom of a more serious issue. If the plant is mostly yellow and the leaves are falling off, this could be a sign of disease. If you notice that the plant looks unhealthy, you should inspect it more closely. Look for signs of disease, like downy basil mildew, on the top and bottom of the leaves.
7 Reasons Basil Leaves Turn Yellow
Here are the most common reasons for basil leaves turning yellow:
1. Too much water
Basil plants can die very quickly if they are overwatered. This herb prefers well-draining soil that is kept slightly moist, but not soggy. Too much moisture can cause the roots of a plant to rot, which prevents the plant from getting the nutrients it needs. One of the first signs that a plant has root rot is when the leaves start to turn yellow. This is more common in basil plants that are grown in pots than in gardens.
Water your garden basil weekly if the weather hasn’t been too wet. Water the plants deeply to promote deep rooting and drought-resistance. Containers require more frequent watering than garden beds, typically every day or two during summer. To see if your basil plants need water, stick your finger into the garden or container soil to gauge moisture levels. You should water your plants if the soil is dry two inches down.
How to fix it (and should you)?
If the roots of your basil plant look rotten, I would advise you to just get rid of the whole plant. The guide also recommends that you do not reuse the soil, or at least make sure it is dry before using it again. Most of the time, it is not worth the effort to try to save a basil plant that has root rot.
Nonetheless, if you want to give it a try, however, here’s what you should do:
- Remove the plant from its pot, and loose the soil surrounding the roots by gently hitting it with your hand. Make sure the soil has had time to dry a bit (this will make the operation easier)
- Leave the roots dry for 1-2 hours at the open air
- Cut the brownish looking roots. This will avoid the bacteria from spreading to the other roots
- Place the plant in new potting soil and pot.
- Avoid to expose the herb to direct sunlight for a couple of days: the plant need to focus on healing its roots after the transplant rather than producing foliage with sunlight triggered photosynthesis
- Wait a week to see what’s happening
The opportunity for survival is not good if more than half the roots are infected. This bacteria typically spreads from root to root.
2: Not enough light
Basil loves sunshine! Place basil in an area that gets 6-8 hours of sunlight per day. This can be challenging if you are growing plants in pots on a balcony or in a garden that doesn’t get much light. It’s worth a try if you have 4-5 hours of sunlight. Just plant the seedlings in your sunniest spot. Choose herbs that can tolerate being in the shade if your sunniest spot only has a few hours of light. Parsley, cilantro, and mint are all good options. Basil won’t grow well in shade and the plants will begin to turn yellow and die.
Many gardeners also want to grow basil indoors during fall, winter, and early spring. If you don’t have the right amount of light, the basil leaves will turn yellow. Pots of basil should be placed in the sunniest window. However, even a south-facing window may not provide enough light for healthy growth. This is especially true if you live in a climate where it snows in the winter. There is a simple solution: a grow light. Tabletop, under counter, and spotlight grow lights are all available for purchase.
If your basil plant is not getting enough sunlight, it might start to wilt and turn yellow. An excess of sunlight can cause black leaves, as discussed in this detailed guide on basil.
3. Cool temperatures
Basil is a sensitive herb that can’t handle extreme temperatures. We do not plant it outdoors early in spring because that is when frost typically occurs. It is best to wait until the temperatures are above 50 Fahrenheit (10 Celsius) during the day and night. You will have the best results if you wait until it is above 60 degrees Fahrenheit (15 degrees Celsius). The plants will not thrive if the temperature is too cold. Yellow leaves on a basil plant are often caused by planting the basil too early. Basil is an herb that is mainly found in the warm Mediterranean area. It typically blooms in late spring or early summer. The University of Nottingham conducted a study that found that any ambient temperature below 15°C will stunt the growth of the plant and make its leaves pale green or yellow.
Basil leaves may turn yellow in late summer and autumn when the weather begins to cool. You should harvest your plants while they are still in good shape and most of the leaves look healthy. You can use pruners or garden snips to cut stems so you can dry the leaves or use them to make pesto.
Basil is an herb that is typically found in the warm Mediterranean area. It is most common in the late spring and summer. Any temperature around or below 15°C will stunt the growth of the plant and make the leaves pale green or yellow. So check the temperature of your room. The yellow leaves on your basil plant are most likely due to the temperature being below 20C.
How to fix a temperature issue?
Check the warmest spot of your house. If the windowsill gets some direct sunlight, it is probably the best place for the plant. Perhaps in a small room with a heater that is mostly warm. If you can’t plant the tree outside, you can create a small greenhouse for the plant.
4. Overcrowded plants
Why is that a problem? If you plant a lot of basil seedlings close together in a pot or garden bed, they’ll do OK at first, but after a while the seedlings will be too crowded and start to do poorly. The first symptom would be yellowing leaves. You need to replant the seedlings individually instead of planting them all in one clump. Another option is to grow your own seedlings, providing them with enough space to grow so you won’t have to worry about overcrowded plants.
Give your basil plants some space when you transplant them into gardens or containers. Plants that are too close together compete for light, moisture, and nutrients, and don’t have enough room to circulate air, which makes them more likely to get sick. All of these issues can trigger yellowing leaves. Most types of basil should be planted eight to twelve inches apart from each other.
5. Plant disease
Belbahrii Peronospora is a pathogen-caused disease similar to a fungus. The most common type of basil is downy mildew, which affects the leaves and stems of the plant. This pest thrives in a highly humid environment without good air circulation, feeding on your basil leaves.
Downy mildew is relatively easy to identify. The first sign is yellowing leaves. Flip those leaves over since it appears always at the bottom side of the leaf as countless black/grey spots that look dust or dirt with the color varying from light grey to black. This organism looks like a fungus, and it spreads through the wind. However, you can also introduce it to your garden through infected seeds or seedlings. If you believe your basil plants have downy mildew, pick all of the unharmed leaves and uproot the plants. There is no treatment.
How to treat downy mildew?
First, remove the plants from their humid area and spread them out to improve aeration. Isolate the plant affected to avoid spreading. You must carefully and gently remove any leaves that are affected by the fungus. You should remember that this fungus spreads through tiny pores that can easily float in the air or be carried by water droplets. Therefore, if the powdery mildew spreads to other leaves, it could potentially damage the rest of the plant.
Another solution is to use an antifungal spray solution. The good news? Preparing them at home with ingredients you probably already have is an option.
For the spray, you need to mix one tablespoon of baking soda, 1 tablespoon of vegetable oil, and one dish of soap in a solution of around 4 liters of water. Spray the solution on affected leaves once a day until the trace of powdery mildew disappears. Easier recipes for garlic bread can be found online, as well as recipes that use milk instead of butter.
Basil does not taste good to big pests like deer, rabbits, and groundhogs, but it can be attractive to smaller insects like Japanese beetles, aphids, or mealy bugs, as well as slugs. If you see holes in leaves, this is a sign that pests have been there. If the leaves are yellow, this could also be a sign of insects such as aphids. Aphids can be a problem for basil plants. These insects can appear suddenly and multiply quickly. Small insects that consume plant juices from leaves come in shades of green, gray, and brown. The damage can cause the leaves to twist and turn yellow. Aphids have the advantage of size; they are very tiny. Even if you are carefully checking your basil, it is easy to miss a dozen individuals that are a millimeter or less in total size.
One single basil plant can withstand being nibbled on by an individual or small colony without suffering any significant damage. However, if hundreds of them gather together, they can easily make a patch of leaves that is completely covered with spots. A massive lack of nutrients will cause the leaves to yellow, wilt, and die. If your basil plant is small, it is likely to die if the infestation is severe.
If you notice yellowing leaves, it is always best to inspect them more closely. If you have an aphid problem, look for them on new growth or beneath leaves. If you see ladybugs or lacewings around aphids, don’t do anything because they are being preyed upon.
7. Potassium Shortage
The lack of potassium in your soil will make your basil’s leaves turn yellow, with the veins remaining green. Basil, as any other herbs need minerals to survive. There are many of them. The most famous fertilizers for basil (due to also the fact that basil as any other plants needs them in large quantities) are potassium, phosphorus, and nitrogen.
One of the hardest deficiencies to spot is lack of potassium. As a general rule, it is a good idea to take notice of where the yellow area is located. Are the spots located between veins or on the edges, as also discussed in this study? If you are experiencing these symptoms, it is likely that you are potassium deficient.
Another way is to go for exclusion. Although it is not certain, the majority of the other causes are easier to test out. Nutrition deficiency problems are, in general, tough to identify.
How to fix potassium deficiency?
In this case, you can add a potassium-rich fertilizer. You can buy them from a nursery or online retailers like Down to Earth on Amazon. It may be easier and cheaper to change the potting soil in the long run. Basil will grow well as long as the potting soil does not contain too much fertilizer.