Eradicating Yellow Leaves on Citrus Plants

Citrus trees are a beloved feature in many New Zealand backyards, offering not only aesthetic appeal but also delicious, homegrown fruit. However, growing healthy citrus trees can be challenging, especially when faced with issues like yellowing leaves. 

Yellow leaves on citrus plants are often a sign of underlying problems, ranging from nutrient deficiencies to diseases or improper care. In this Jim’s Mowing NZ blog, we’ll explore the common causes of yellow leaves, how to diagnose the issue, and the best ways to treat and prevent it. By the end, you’ll have a clear understanding of how to keep your citrus trees thriving and productive.

Why Do Citrus Leaves Turn Yellow?

Yellowing leaves, also known as chlorosis, are a common issue for citrus trees. This condition occurs when the leaves lose their green pigment (chlorophyll) due to a lack of essential nutrients, poor soil conditions, or disease. While it can be alarming to see your citrus tree’s leaves turning yellow, the good news is that most causes are treatable if identified early.

Let’s dive into the most common reasons for yellow leaves and how to address them.

1. Iron Deficiency –  A Leading Cause of Chlorosis

One of the most common causes of yellow leaves in citrus trees is iron deficiency. This condition is particularly prevalent in alkaline soils, which are common in parts of New Zealand. When a citrus tree lacks iron, its leaves turn yellow while the veins remain dark green. This distinctive pattern is a clear indicator of iron chlorosis.

How to Treat Iron Deficiency

• Iron Chelates – The most effective treatment for iron deficiency is applying iron chelates. These are readily available at garden centers and are easy to use. Simply mix the iron chelates according to the packet instructions and spray the solution onto the foliage. For larger trees, you can water the solution around the root zone using a watering can.
• Soil pH Adjustment – Since iron deficiency is often linked to alkaline soil, consider testing your soil’s pH. If the pH is too high, you can lower it by adding sulfur or organic matter like compost. This will make iron more accessible to the tree’s roots.
• Timing – Apply iron chelates during the growing season for the best results. You should notice improvements within 3–4 days in warmer climates. 

If you are unsure how to determine and treat Iron Deficiency in your plants, an expert gardener can be of help.

2. Magnesium Deficiency – A Silent Culprit

Magnesium is another essential nutrient for citrus trees, playing a critical role in chlorophyll production. Without sufficient magnesium, citrus trees cannot produce the sugars and starches needed for growth, leading to yellowing leaves and poor fruit development.

Identifying Magnesium Deficiency

Magnesium deficiency is most noticeable in autumn, as the nutrient is heavily utilized during fruit development. Symptoms include yellowing between the leaf veins, while the veins themselves remain green. Older leaves are often affected first, as magnesium is mobile within the plant and is redirected to newer growth when in short supply.

How to Treat Magnesium Deficiency

• Epsom Salts – A simple and effective remedy is applying Epsom salts (magnesium sulfate). Dissolve 1–2 tablespoons of Epsom salts in a gallon of water and apply it to the soil around the tree. Repeat this process every 4–6 weeks during the growing season.
• Balanced Fertilizer – Use a citrus-specific fertilizer that contains magnesium. Regular feeding will help prevent future deficiencies.

3. Overwatering or Poor Drainage

While nutrient deficiencies are a common cause of yellow leaves, overwatering or poor drainage can also lead to similar symptoms. Citrus trees prefer well-draining soil, and waterlogged roots can cause stress, leading to yellowing leaves and even root rot.

How to Fix Overwatering Issues

• Check Soil Moisture – Before watering, check the soil’s moisture level by sticking your finger about 2–3 inches into the soil. If it feels wet, hold off on watering.
• Improve Drainage – If your soil retains too much water, consider amending it with sand or organic matter to improve drainage. Alternatively, plant your citrus tree in a raised bed or container with drainage holes.

4. Lack of Fertilizer – Feeding Your Citrus Tree

Citrus trees are heavy feeders, meaning they require a steady supply of nutrients to stay healthy and productive. A lack of fertilizer, particularly nitrogen, can lead to yellow leaves and poor growth.

How to Properly Fertilize Citrus Trees

• Choose the Right Fertilizer – Use a balanced citrus fertilizer with a higher nitrogen content. Look for a ratio like 3:1:1 (nitrogen, phosphorus, potassium).
• Follow a Schedule – Fertilize your citrus tree regularly, typically every 4–6 weeks during the growing season. Reduce feeding in winter when the tree is dormant.
• Apply Evenly – Spread the fertilizer evenly around the tree’s drip line (the area beneath the outermost branches) and water thoroughly after application.

5. Alternaria Brown Spot – A Fungal Disease

Another potential cause of yellow leaves is Alternaria brown spot, a fungal disease that affects citrus trees. This disease is characterized by brown spots on the leaves, often surrounded by yellow halos. It primarily affects young leaves and shoots, leading to defoliation if left untreated.

How to Treat Alternaria Brown Spot

• Copper Fungicides – Apply copper-based fungicides in spring when the leaves are half-expanded. A second application may be needed when the foliage is fully expanded.
• Prune Affected Areas – Remove and dispose of any infected leaves or branches to prevent the disease from spreading.
• Preventive Measures – Maintain good air circulation around the tree by pruning regularly. Avoid overhead watering, as wet foliage can encourage fungal growth.

6. Pest Infestations – A Hidden Threat

Pests like aphids, spider mites, and scale insects can also cause yellowing leaves by sucking sap from the tree. These pests weaken the tree and can introduce diseases, further exacerbating the problem.

How to Manage Pests

• Inspect Regularly – Check your citrus tree regularly for signs of pests, such as sticky residue, webbing, or visible insects.
• Natural Remedies – Use insecticidal soap or neem oil to control pest populations. These treatments are effective and environmentally friendly.
• Encourage Beneficial Insects – Introduce beneficial insects like ladybugs, which feed on common citrus pests.

Preventing Yellow Leaves

Prevention is always better than cure when it comes to maintaining healthy citrus trees. Here are some general tips to keep your trees in top condition:

• Test Your Soil – Regularly test your soil’s pH and nutrient levels to ensure it meets the needs of citrus trees.
• Water Wisely – Water deeply but infrequently, allowing the soil to dry out slightly between waterings.
• Mulch – Apply a layer of organic mulch around the base of the tree to retain moisture and regulate soil temperature.
• Prune Regularly – Remove dead or diseased branches to improve air circulation and reduce the risk of disease.

When to Call a Professional

While many issues can be resolved with proper care and treatment, some situations may require professional assistance. If your citrus tree continues to struggle despite your best efforts, consider consulting a local arborist or gardening expert. They can provide tailored advice and help you address any underlying issues.

Conclusion

Yellow leaves on citrus trees are a common but treatable problem. By understanding the causes—whether it’s nutrient deficiencies, overwatering, fungal diseases, or pests—you can take the necessary steps to restore your tree’s health. Regular care, including proper fertilization, watering, and pest management, will go a long way in preventing yellow leaves and ensuring a bountiful harvest.

If you need help maintaining your citrus trees or other garden plants, don’t hesitate to reach out to Jim’s Mowing NZ. Call us on 0800 454 654 or book online for a free, no-obligation quote. Let us help you keep your garden lush, healthy, and vibrant!