Growing basil is a joy for many gardeners. Its aromatic leaves lend flavor and fragrance to dishes from pesto to caprese salad. However, nothing is more disappointing than walking out to your herb garden and noticing those once vibrant green leaves have turned yellow.
Basil plants usually have yellow leaves when they are stressed. The plant is trying to tell you that something is wrong with the way it is growing. The key is to figure out what is wrong so you can fix it and bring your basil back to life.
Why do basil leaves turn yellow most of the time? Here’s what you can do to fix it:
Overwatering
One of the main reasons basil leaves turn yellow is too much water. The plant prefers consistently moist but not soggy soil. Root rot and lack of oxygen for the roots are caused by too much water.
Check the soil with your finger before watering. It should not be muddy or saturated. Let the top few inches of soil dry out a bit between waterings. Make sure pots have drainage holes. Water less frequently but deeply vs frequent light watering.
Under Watering
While overwatering is more common, underwatering can also cause yellowing. Basil needs a steady supply of moisture. If the soil dries out too much, the plant will wilt and struggle.
Check soil moisture every few days. Water when the top few inches become dry. Avoid extremes of bone dry or sopping wet soil. Aim for a happy medium.
Nutrient Deficiency
Lack of nitrogen, phosphorus, potassium or other key nutrients leads to yellowing leaves. Fertilize with a balanced organic fertilizer or compost tea every 2-3 weeks in the growing season.
Potassium deficiency shows up as yellowing around the leaf margins and tips first. Apply kelp meal or banana peels for an organic potassium boost.
Diseases
Fungal diseases like downy mildew or fusarium wilt can cause yellowing. Downy mildew looks like grayish fuzzy spots on leaf undersides. Remove infected plants immediately to avoid spreading.
For fusarium wilt, pull plants at first signs of wilt and yellowing leaves. Sterilize tools and containers to prevent spread.
Pests
Hungry insects like aphids, Japanese beetles, and caterpillars will munch on leaves causing yellowing or holes. Check leaf undersides for pests. Use neem oil or insecticidal soap sprays to treat infestations.
Cold Temperatures
Basil thrives in warm weather above 70°F. Cool spring or autumn temperatures can cause yellowing and stunted growth. Use row covers or cloches to protect plants if nights drop below 50°F.
Insufficient Light
At least 6 hours of direct sun is needed for happy basil plants. Too much shade from trees or buildings leads to sparse and yellow growth. Move containers to maximize sunlight or use grow lights.
Transplant Shock
Young seedlings may show some yellowing or wilting after being moved from indoor conditions to the garden. This is normal as they adjust. Make sure to harden off plants first and water well after transplanting.
Going to Seed
As basil matures, it bolts or goes to flower. The plant stops producing leaves and focuses energy on seed production. Pinch off flowers regularly to prolong harvest. But some yellowing is inevitable.
Air Pollution
High ozone, sulfur dioxide, or other air pollutants can burn leaf tips and cause yellow spots. Not much you can do except wash leaves to remove particulate matter. Plant away from roads or factories if possible.
Age
Older basil plants near the end of their life cycle often yellow or decline in vigor. Basil grown as an annual only lives one season. Consider it a sign to pull up old plants and sow new seeds.
Root Disturbance
If basil was repotted or divided late in the season, having its roots disturbed can shock the plant leading to yellowing leaves as it recovers. Leave it alone and water gently until new white roots establish.
Impaired Roots
Root issues like rot, restriction, or nematodes reduce the plant’s ability to take up water and nutrients. Examine roots for signs of problems and improve drainage if soil is too heavy.
Natural Leaf Drop
As part of its normal growth cycle, basil will drop its oldest lower leaves. Some yellowing accompanies this natural shedding. As long as it’s just a few leaves and new growth is healthy, it’s nothing to worry about.
Hot Temperatures
Once temperatures climb above 85°F, some varieties of basil struggle with scorching and yellowing. Switch to a heat-tolerant variety like ‘Spicy Globe’ or add shade cloth to protect plants during heat waves.
Calcium Deficiency
Yellow leaf margins that curve downward indicate a calcium deficiency. Apply a foliar spray of calcium nitrate or crushed eggshells dissolved in water to supply the calcium basil needs.
Recent Transplant
Young basil seedlings often show some yellowing and stress after being moved from indoor conditions to the garden. As long as new growth looks healthy, it should adjust in a week or two.
Excess Fertilizer
Over-fertilizing can scorch and yellow leaves. Flush soil with water to remove excess salts. Avoid high nitrogen synthetic fertilizers which easily burn plants. Stick to organic fertilizers applied per instructions.
Compacted Soil
Dense, heavy, compacted soil prevents air and water from penetrating to plant roots. Loosen soil and add organic material like compost to improve texture for healthy basil growth.
High pH Soil
Basil prefers a slightly acidic soil pH between 6.0-6.5. Overly alkaline soils above 7.0 can make nutrients unavailable leading to deficiency and yellowing. Test soil and amend with elemental sulfur if needed.
Natural Variegation
Some basil varieties like ‘African Blue’ and ‘Red Rubin’ have naturally variegated leaves. Yellow spots and patterns are normal for these cultivars and not a sign of problems.
Bottom Leaves Naturally Yellow
The lowest, oldest leaves on the plant will eventually yellow and drop off. This natural aging process clears room for new growth. It’s only a concern if middle and upper leaves start yellowing too.
Genetic Predisposition
Certain basil varieties and cultivars are more prone to leaf chlorosis and yellowing. ‘Genovese’ and ‘Sweet’ basil tend to be weaker while ‘Thai’ and ‘Spicy Globe’ have higher tolerance.
Excessive Pruning
While pinching helps produce bushier basil plants, over-pruning can stress the plant leading to yellowing. Avoid removing more than 20% of the plant at one time and don’t prune right before frost.
Inadequate Air Circulation
When properly pruned, basil grows into a bushy form with plenty of dense foliage. Because of this, it is important to give each plant a lot of space and to harvest the right way at the right time of year so that the plants’ blood flows well.
Keeping the center of the plant open prevents leaves from compacting together which causes wilting and yellowing and reduces the harvest.
Overwatering
Basil roots can rot if they get too much water, which makes the plant wilt and lower leaves turn yellow.
A finger poke or a moisture meter can be used to measure the soil’s moisture level to find out if the basil leaves are yellow because they were overwatered. Potted plants may need to be moved into a new pot with fresh, dry potting mix. For in-ground plants, hold off on irrigating until soil has had a chance to dry out.
To prevent root rot, allow the top 2 inches of soil to dry between waterings and make sure potted plants have plenty of drainage holes. If youre growing basil in a pot, be sure to drain off all excess water before returning the plant to its saucer.
Why YOUR Basil Leaves are SECRETLY Turning Yellow?!
FAQ
What does an overwatered basil plant look like?
If you water your basil plant too much, it will probably show signs of stress, like leaves turning yellow or brown, wilting, and maybe even black spots or mushy, smelly roots from root rot.
Do basil plants need direct sunlight?
Yes, basil plants generally need a lot of sunlight. For optimal growth and flavor, they require at least 6 to 8 hours of direct sunlight per day. If you’re growing basil indoors, ensure it receives bright, indirect sunlight or supplement with grow lights.
Can a yellow leaf turn green again?
No, a leaf that has turned completely yellow generally cannot turn green again. Once a leaf loses its chlorophyll (the pigment that makes it green), it’s usually a sign of cell damage or the natural aging process, and the chlorophyll cannot be restored.
How do you perk up a basil plant?
The key to reviving a wilting basil plant is to keep the soil consistently moist, locate the basil in an area of morning sun followed by afternoon shade and shelter the basil from excess winds. After a good soak, the wilted basil should revive. It really looks like it has drought stress.