Why Do Agapanthus Leaves Turn Yellow? Tips to Fix

The leaves of agapanthus plants are long and strap-like in appearance. Another distinguishing feature of the leaves of these plants is their distinctly vibrant green color. Thus if Agapanthus Leaves Turn Yellow, you would be concerned.

Agapanthus leaves turning yellow indicate a deeper problem with your plant or the environment it is growing in. 

Reasons, why Agapanthus leaves turn yellow, are:

  • Iron deficiency
  • Pests
  • Diseases
  • Excessive watering
  • Sunburn (prolonged sun exposure)

#1- Iron Deficiency Causing Agapanthus Leaves Turn Yellow

The yellowing of leaves with green veins is a true sign of chlorosis.

All plants require iron to carry out reactions, grow and eventually produce flowers. This iron deficiency is not like other nutrient deficiencies. Adding an iron supplement to the soil will not solve the problem. 

Yellow agapanthus leaves denote chlorosis, a lack of the green pigment – chlorophyll. One cause of this condition is the inability of the plant to absorb or utilize iron properly.

An artificial application of iron on the agapanthus leaves acts as a short-term solution. 

The leading cause of failure to exploit iron present in the soil is high soil pH or a lack of it completely. 


  • Gradual yellowing of all areas of the leaf except the leaf veins which remain green. 
  • Yellowing mostly occurs on new growth. 
  • If yellow foliage is noticed take a soil test or pH test kit that will show the soil as alkaline (pH 7 and above). 


To assist your Lily of the Nile in taking up iron, you must lower the pH. Ideally, a pH of 6.5 will result in better iron uptake. 

You can effectively lower soil pH by adding Sulfur. Generally, a 12-pound application of sulfur or acidifying fertilizer (containing sulfur) can lower pH by one point. 

NOTE: Different acidifying fertilizers have different directions. Follow the instructions given on the label for the best results. 

Scatter the sulfur/acidifier onto the soil and then water it immediately. Check the soil pH after a few weeks.

Is your agapanthus green and healthy but not blooming? Find out why your agapanthus isn’t flowering. 


Every gardener knows another reason why discoloration occurs in garden plants and even fruit trees! Pests can cause yellow or brown discoloration in plants, including agapanthus. 

The unfortunate news is that completely yellow agapanthus leaves usually mean the insects have already taken what they wanted and left!

So, it’s best to catch them in the act or prevent them altogether. 

Both spider mites and mealybugs feed on the sap flowing through the plant. They use the leaves as an access point and may not be visible if they are feeding on the underside of the leaves. 

Let’s look at these agapanthus pests individually. 

Spider Mites (​Tetranychus urticae​) 

These very small insects infest plants like the agapanthus in high numbers, easily reaching hundreds when left unnoticed. They appear to look like small spiders or ticks. However, don’t be fooled by their small size, they can do damage!

These pests attach to the leaves, penetrate the leaves with their mouthparts, and then feed on the sap.

Areas that have been fed on are evident with small spots of yellow. As time passes, these small yellow patches can extend to make agapanthus leaves turn yellow.

Mealybugs (Pseudococcidae​)

You will find it easier to identify mealybugs. They are small white insects that in large numbers look like white mold. Again, they feed on the sap of agapanthus leaves. 

Mealybugs use a different feeding approach than spider mites. Instead of puncturing the leaf, they scrape the top layer of the leaf off. 


  • Small yellow spots or completely yellow leaves on your agapanthus plant.
  • Wilting of leaves with discoloration. 
  • Minute insects in clumps that appear red or brown in color (with respect to red mites).
  • The appearance of fluffy white areas 


As is the case with large infestations, a means of removing the majority of them within the shortest time is crucial.

A store-bought insecticidal solution can be used as a spray and applied to both the top and underside of the agapanthus leaves. There should be instructions to follow on the container of the insecticide. Usually, a weekly spray is necessary. 

These insecticidal sprays could be harmful to other insects. Therefore, spray your agapanthus plant on a windless day to avoid the unnecessary spread of the chemical.

Also, protect the spray from leaching into water sources as it is dangerous to aquatic life.   

#3 – Disease 

Diseases are a common problem and can infect any plant when the conditions allow it. Most diseases of agapanthus are fungus-based. These as well cause Agapanthus Leaves Turn Yellow.

Moist soil and shaded conditions favor the growth of fungus. Watering efforts do play a large role in diseases.

Avoiding the conditions that induce fungal growth will be most effective in preventing poor growth and health of agapanthus plants. 

A few fungal problems agapanthus plants are: Root Rot, Leaf Spot, Fungus Gnats (​Bradysia coprophilia​) 


  • Discoloration such as yellowing of the leaves of an agapanthus. 
  • Poor appearance of the plant due to root rot. 


Immediately remove infected parts of the plant. Keep them away from other plants. Dispose of them well to prevent any chances of the spores spreading- they are hardy!

Then, apply a fungicide to the plants and soil to prevent further spread. 

The key to stopping and preventing fungal infections is to make it impossible for them to survive in the current conditions.

This means spacing plants out and placing them in the sunlight. This ensures damp and cool conditions that support fungi are eliminated. 

#4 – Excessive Watering 

Agapanthus is not a demanding plant. Due to its minimal water requirements, it is often termed a drought-hardy plant. This makes it obvious that these plants do better with less water than more.

Overwatering is a common reason why agapanthus leaves turn yellow. The yellow leaves may cause some gardeners to think it is underwatering that is creating this effect. 


  • Yellowing of leaves occurs from the bottom-most leaves. 
  • Wet soil that doesn’t appear to be drying. 
  • The poor overall health of the plant is due to root rot.  


Avoid overwatering by checking the soil first. Water your agapanthus only if the soil is dry. Dip your finger into the soil to assess how moist it is. 

Use a moisture meter to help you determine the soil’s moisture. This apparatus is also effective in helping you water your agapanthus correctly- only when needed. 

Stop watering efforts if there has been considerable rainfall or the soil looks wet from the last watering. 

To prevent wet conditions that favor bacterial growth, water from the base up. Watering from the leaves first could create pockets of moisture.  

Read why lemon tree leaves turn yellow and how to fix it. 

#5-Excessive Heat and Sun

Agapanthus plants prefer hot climates over colder climates. However, sometimes it may get too hot for them to handle! In such cases, high temperatures and extended exposure to intense sunlight cause yellowing of agapanthus leaves. 

A combination of reasons may cause your agapanthus leaves to turn yellow in a hot climate. 

Yellow agapanthus leaves are possible in hot climates where the plants are positioned in a location with high sun exposure.

The intensity of the sun, temperature and watering efforts also play a role in whether leaves turn yellow or not. 


  • Yellowing initiates from the tips and edges of the agapanthus leaves. 
  • Slight limping of agapanthus leaves could confirm dehydration and sunburn may ensue.  
  • Drought and hot temperatures are conditions that may induce sunburn. 


Provide shade to your agapanthus, especially when hot dry spells are on the way. Preferably afternoon shade is best for the plants as the sun can be most intense during this time. 

Techniques that help to retain moisture will be welcomed. This includes adding a layer of mulch around agapanthus plants. A layer of straw grass clippings can act as mulch, protecting the plants. 

High temperatures and dry spells usually cause rapid drying out of the soil. If the mulch still can’t help with this perhaps you should increase watering efforts. But, check the soil every time before watering! 


Your agapanthus won’t be beautifying your garden much if its leaves turn yellow! You will have to act fast and identify the cause as soon as possible. Only then will you be able to correct and reverse the effects if possible. 

Possible causes for agapanthus leaves turning yellow are Iron deficiency, Pests, Diseases, Excessive watering, and Sunburn (prolonged sun exposure). 

Fixing yellow leaves can involve amending soil pH, using pesticides and fungicides, watering correctly, and providing shade. 

If all conditions are corrected and you read the signs in time, you can expect to have a healthy agapanthus plant! 

Want the best for your agapanthus plant? Here’s where to plant agapanthus to receive the best conditions. 


Should I cut yellow leaves off Agapanthus?

Yes, you can cut off yellow agapanthus leaves as it is not likely they will become green if they are totally yellow. You could wait for them to fall off, but cutting them off early can help to reroute energy.

Why are my Agapanthus leaves brown?

Brown agapanthus leaves usually show your plant is receiving too much sunlight. Provide a bit more shade and water to them to stop the other leaves from turning brown.