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Why are Basil Leaves Turning Yellow?

Are you stunned after seeing the cupped green leaves of your Basil turning yellow? Well, the change could be due to mishaps in the care.

Generally, yellowing leaves are signs of a sick Basil plant caused by improper watering, too little sun, insufficient nutrients, wrong potting mix, fungal diseases, and many more. However, the situation can be reversed if noticed and applied on time solution.

Continue till the end if you are suspicious that any of these factors are causing the yellow leaves in Basil to learn its instant care tips.

Basil Leaves Turning Yellow: Is it Normal?

The occurrence of yellow leaves in Basil during the late summer or the early fall is normal as it is the end of the growing season.

However, it is not normal for Basil leaves to turn yellow despite caring for them regularly, as the plant may be dying.

The discoloration and yellowing due to environmental stress start at the petal base.

So, start with determining the yellowish shade (pale or full), the number of yellowing leaves, and the frequency of yellowing.

Then you can begin looking for possible problems with your plant.

What Causes Basil Leaves to Turn Yellow?

Yellowing Basil leaves aren’t limited to the problems of overwatering, lack of sunlight, or nutrient deficiency.

Failing to provide the proper growing condition to the Basil plant will cause yellowing leaves. Too much or too little of anything will also alter the leaf’s natural color.

Sometimes, growing these plants indoors will also affect their health because Basil needs six to eight hours of sunlight.

Like these, there are varying factors that may affect your Basil plant.

Before jumping ahead, let’s look at all these probable causes.

1. Excess watering

Excess watering is the leading cause of turning the Basil leaves yellow.

Although regular watering is needed for Basil’s healthy growth, too much water will suffocate its roots and cause root rot.

This is more likely with indoor Basil plants grown in a small pot without proper drainage.

Basil plants require slightly moist soil to help spread their roots, but overwatering them will drain the mud off of roots and hamper their natural growth.

You can determine ‘root rot’ by inspecting the yellowing leaves. It indicates overwatering if the leaves feel soft and limp, with new growth failing.

Immediate Solution

  • In case of an overwatered plant, stop all irrigation immediately.
  • Place the pot under direct sun for 24 hours to let the soil dry out completely.
  • Use newspaper to soak excess moisture from the soil.
  • Keep watering to a minimum because slightly dry soil is healthier for the basil plant.
  • If rain is forecasted, bring your plant inside immediately.

Consider deep watering your outdoor basil plants every seven to ten days.

For indoor plants, water less frequently. Let the topsoil (1 to 2 inches) dry out before watering again.

Quick Tip: Water once every two to three days in hot weather, such as in times of drought.

If the yellowing doesn’t stop, consider sliding your plant out of the soil to check for possible root rot.

Plants with minimal root rot can be salvaged, but those with worsened root rot must be thrown away.

2. Too Compact Potting Mix

The compact soil is another primary reason for yellowing leaves because the too-tight potting mix will suffocate its roots and hamper its natural growth.

The clay soil found in most potting mixes and backyards drains very slowly and then hardens, causing a compact potting mix.
A terracotta pot containing the yellow leaves of Basil is lying over a table along other indoor plant.
Too dry soil can be the reason behind the soil’s compactness, causing the leaves to turn yellow.

When the soil doesn’t get enough moisture, it becomes hydrophobic and stops absorbing moisture altogether.

Sometimes, too much nitrogen content will make the soil compact, like the soil found in most gardens or fields.

Poke your finger into the ground to further probe into the matter. If the ground underneath feels drier, it is a compact potting problem.

Immediate Solution

  • Amend by adding pebbles and small rocks to the existing mix to increase the porosity.
  • Add compost to increase the aeration of the mix rich in clay particles.
  • As for the ground, loosen the soil with a broad fork and till the topsoil.
  • You can also try adding mulch to increase aeration.
  • If the condition is irreversible, prepare another mix using potting soil, peat moss or compost, and perlite in a 1:1:1 ratio or use a readily available cactus mix.

3. Lack of Nutrients

Young leaves of Basil start curling downward with discoloring of leaves starting from veins, which later turn prominently yellow due to lack of Potassium.

You’d also see browning of leaf edges and tips.

Using soil from land that has experienced erosion, runoff, leaching, and burning crop residues will wither your Basil plant and turn its leaves yellow.

This soil lacks good bacteria and inorganic salts like calcium and magnesium vital for plant growth.

Furthermore, you can determine nutrient deficiency symptoms by checking for visual signs, problems with new foliage and stunted growth.

Immediate Solution

  • Conduct a soil nutrient analysis to determine the nutrient lacking in the soil mix.
  • Feed your basil plants with a good mix of organic fertilizer every two to three weeks.
  • For indoor plants, consider fertilizing them every four to six weeks. Consider picking a 10-10-10 organic fertilizer.
  • You can also feed them a Kelp meal, Bone meal, and wood ash to boost their nutrient supply.

Basil plant struggles to absorb iron from the soil because it’s an immobile nutrient. Hence, most gardeners suggest feeding iron through a foliar spray.

4. Wrong Soil pH

Remember, a Basil plant prefers a soil pH between 6 to 7.5, which is slightly acidic.

A wrong soil pH causes plant poisoning that affects the growth of your Basil plant and healthy green leaves.

Too acidic soil releases aluminum that can poison the plant, whereas too alkaline soil locks the nutrients and makes them unavailable to plant roots.

Start with determining if your soil is lacking the correct pH. Get a pH check done by a professional, or get yourself a pH test kit.

Alternatively, you can analyze physical symptoms like the bottom leaves of Basil turning yellow with the green leaves at the top.

A rapid loss of organic matter, such as soil bacteria and minerals or too much nitrogen and sulfur-rich fertilizer, can also cause soil pH to alter.

Immediate Solution

  • Amend soil with organic mulch immediately after a frost with perfect moisture, pH level, and major nutrients required for growing basil seedlings.
  • Add Sphagnum peat, limestone, and iron sulfate to balance the soil’s acidity.
  • Alternatively, mix one tablespoon of baking soda in a gallon of water and spray over the plant to either increase or decrease the level.
  • You can also use organic feed like Dr. Earth Organic Fertilizer to amend the soil pH.
  • If the situation does not recover, try using a new potting mix with a balanced pH level.

Basil plants have common fungal diseases, like Fusarium wilt and Downy mildew, which eat up plant nutrients and lead them to turn yellow.

Downy mildew is a quick-spreading fungus identifiable by a fuzzy, gray, or brown-looking substance on the plant leaves, while Fusarium wilt invites root rot, causing a foul smell from the soil.

Some other signs include the appearance of yellow, light green, black, or purple spots on the leaves, with the bottom ones affected first and then moving up.

Infected leaves first turn yellow around the central veins, then start covering the entire leaves.

So, if you find two or more of these signs on the Basil leaves, you can conclude that your plant suffers from fungal disease.

Immediate Solution

  • Isolate the affected Basil plant from the healthy ones to prevent further spread.
  • Directly use the fungicides like chlorothalonil and mancozeb over the fungus to protect against early infections.
  • Increase airflow and sunlight to curb mildew infection to some extent.
  • Alternatively, you can use fungicides containing sulfur, lime sulfur, and mint oil to prevent mildew.

6. Inadequate Light and Cooler Temperature

Basil plants are summer day lovers requiring direct sun for at least 6-8 hours daily and a temperature of 80-90ºF.

However, ignoring the light requirement of the Basil plant and placing them even in the slightest shade can affect its leaf color.

Inadequate light invites cooler days and fluctuates the temperature around the Basil plant.

Meanwhile, with the shade and all the colder days, you should never try transplanting the Basil plant as it may turn the leaves entirely yellow and wither out the plant.

However, if the yellowing occurs at the end of the summer or the beginning of the frost, it is entirely due to the inactive season and is normal.

Immediate Solution

  • Move the plant away from the shade and place it in a south-facing window.
  • If indoors have insufficient light, move the plant outdoors during the day.
  • Install grow lights and place the Basil plant under them for at least 16 hours daily.
  • Relocate the plant if near a radiator or heating vents to prevent the fluctuating temperature.
  • Put heating mats under the pot to maintain a steady warmth to the Basil plant.

7. Pests and Predators

Similarly, tiny pests like Aphids, caterpillars, and root-knot nematodes will spread diseases turning Basil leaves yellow.

Aphids and Root-knot nematodes are tiny pests that suck the water from Basil’s foliage, leaving them high and dry. In addition, caterpillars, especially Cutworms, often attack Basil plants.

Cutworms tend to feed on the plant closer to the ground. They are generally an inch long with green or brown skin.

These predators are attracted by green, lush leaves and may travel ten meters from their initial plant to feast on the Basil plant.

They feast on the leaves and shoots, only to hatch eggs that later become more plant-eating larvae.

Immediate Solution

  • Using nematicide directly on the soil kills nematodes, but be wary about using it in excess, as it can kill most living organisms it comes in contact with.
  • Use insecticidal soap to kill Aphids, but avoid using them when the sun is directly up as it can leave the plant scorched.
  • Pick and remove caterpillars from the plant and drop them into a soapy solution to kill them immediately.
  • Spread Diatomaceous Earth (D.E.) to kill cutworms instantaneously.
  • To prevent future infestation, spray a homemade solution of Canola oil and liquid dish soap mixed with warm water to flush tiny caterpillar eggs.

8. A Dying Plant

Excessive yellowing leaves accompanied by flower buds may suggest that your Basil plant is dying.

However, in some cases, flower buds may appear before the leaves start getting yellow.

Other tell-tale signs include brown or dark leaves, falling petals, wood-like stems, and the looping posture of the plant.

Basil plants commonly grown at home may only live one growing season, typically six to nine months, before dying.

You can fix it by propagating your plant, cutting a few parts, and changing the soil, but trying to fix a dying plant from untreatable root rot, frost, and plant-related diseases will be useless.

Any factors mentioned above that cause yellowing leaves may kill your plant unless you treat them in time.

How to Prevent Basil Leaves from Turning Yellow?

Basil plants can easily survive when adequately taken care of; otherwise, your plant will hardly survive up to six months.

Consider these handy tips to ensure your Basil leaves remain full throughout the year.

  • For Basil in pots, water once every three to four days, and for Basil in the garden, water at least once every two to three days during summer.
  • Check the sun pattern in your location and place your potted plant in the right direction to receive the most sun.
  • Harvest a few leaves from the top down and cut half the total stem length to ensure healthy growth.
  • Regularly trim the woody stem tips to discourage flower growth on the Basil plant.
  • Consider planting basil seedlings indoors for two weeks before moving them outside in a larger pot or garden sunlight.
  • For adult Basil plants, changing soil can be done once a year or two to ensure they get fresh soil and nutrients.
  • Buy a Basil pot with suitable drainage holes.
  • Share the garden space with other similar crops such as tomatoes, lettuce, parsley, and peppers that help to exchange nutrients among the plants.
  • Use all-purpose fertilizer with NPK 10-10-10 to significantly boost your new plant.

To Wrap It Up

The early frost, bacterial infection, and poor nutrition can turn your Basil leaves yellow and cause black spots to appear along with yellowing.

So, minimize the damage by cutting away leaves with black spots and pale discoloration and placing the plant in a sunny area.

With the correct insights, you can prevent Basil leaves from yellowing.

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