Whether you have a dwarf tree or an entire fruit tree orchard, something is satisfying about owning citrus trees. While generally easy to care for, a lemon tree and citrus come with a list of potential health problems.
Unfortunately, these problems often share symptoms, making it difficult to diagnose and treat if you don’t know what to look for. A good example is when the lemon tree leaves are turning yellow and starting to curl.
Several potential causes require very different treatments.
Let’s look at these causes and what you can do to diagnose and treat them.
Why Are My Lemon Tree Leaves Curling and Turning Yellow?
Something to remember is that lemon tree leaves turning yellow and yellowing are two different symptoms that sometimes overlap.
This means you will need to address the two symptoms separately and consider them signs of a single problem.
Common Causes of Lemon Tree Leaves Curling
Curling leaves are often the more manageable symptom to diagnose.
On their own, leaves that curl upwards signify that the plant is responding to rapid temperature changes.
This symptom is especially prevalent during heat waves.
Meanwhile, lemon tree leaves curling downwards signify potassium deficiency, especially on lemon or lime trees.
This is usually not a problem with a proper fertilization regimen, but it can still happen if your fertilizer doesn’t have the best NPK ratio.
Common Causes of Lemon Tree Leaves Turning Yellow
Proper nutrition is also a leading cause of citrus leaves turning yellow.
Yellow leaves may indicate low nitrogen content or a pH issue.
Iron will cause smaller, stunted yellow leaves on the plant.
Resource management is a critical cause of yellowing, either as spotting or throughout the leaf, and may also involve some leaf drop.
This problem happens when the plant bears fruit and is perfectly natural.
Unfortunately, it resembles other issues, so I always hope this is the cause but use a process of elimination to confirm it.
Related: Why Meyer Lemon Trees Turn Yellow?
Common Problems Leading to Both Symptoms
Overwatering is perhaps the most common cause of curling leaves and turning yellow.
This is especially true of orange trees, which are more sensitive to water issues.
In extreme cases, the plant may be suffering from root rot, which will prevent it from drinking properly.
Inadequate watering conditions such as drought can also create both symptoms, so consider the soil moisture and weather conditions to determine whether you’re giving it too much or too little water.
Fungal diseases can cause discoloration, curling, and leaf drop.
Botrytis disease and bacterial blast are two infections that lead to leaf curling.
Other common fungal issues are powdery mildew and sooty mold, which can be a side effect of infestations.
Speaking of insect infestations, aphids, mealybugs, spider mites, and scale are all common citrus pests that drink the sap out of your plant’s leaves.
This can cause yellow spots (sometimes ringed by brown) and leaf curls.
Their frass, called honeydew, attracts ants and is a breeding ground for fungal infections.
Zeroing in on the Cause
As you can see, there are a lot of problems that can cause curling and/or yellowing.
Knowing which you’re facing will allow you to treat the tree properly, which means a process of elimination.
Begin by checking the yellowing leaves carefully for any signs of an infestation or infection.
Seeing many ants marching to and from your tree is often a good indicator that they’re harvesting honeydew from an infestation.
Regarding water issues, stick a finger or moisture meter in the soil to see how dry it is (and how far down), considering that citrus trees generally have shallow roots.
Consider recent weather conditions such as heat waves, short cold fronts, or storms.
Finally, use a soil test to check for deficiencies.
You can up a soil test kit from your local garden center (or order one online).
Check for nutrient deficiencies in potassium (curling), pH, or nitrogen (both causing yellowing).
Next, find out the ideal pH and soil NPK recommendations for your particular plant and compare that to your test results to see what may be missing.
In the case of malnutrition, a little feeding is usually all the plant needs.
Purchase a citrus fertilizer to restore the identified deficiencies based on the test results.
You may also choose to apply neem cakes (NPK varies but is often 4-1-2) and/or coffee grounds along with the fertilizer for additional benefits.
Proper watering habits are essential for protecting your plant from rot and many pests, as well as preventing yellow, curling leaves.
For dwarf and potted citrus plants, water when the soil is dry to the touch 2 to 3” inches down.
Water slowly and deeply until it begins to seep out of the drainage holes.
For planted trees, it’s a general rule of thumb to water once per week for younger plants and monthly for adult trees.
In both cases, five gallons is usually enough per tree.
Avoid aiming sprinklers at the tree and adjust the amount of water needed based on recent rainfall.
Infestations and infections can be a more annoying problem, as trees can be difficult to spray properly.
Neem foliar sprays can help combat infestations but must thoroughly coat the tree to be effective.
Natural predators, like ladybugs or parasitic wasps, can help control the population as long as you ensure the ants cannot defend their cattle.
Meanwhile, copper sprays can help with fungal infections but again must hit the fungus to work.
By far, the best solution for infestations (and some fungal and bacterial infections) is a neem soil soak.
A potted tree will only need 2 to 4 cups (and a bit more if they’ve reached full size), while planted trees will require more.
The soak becomes a systemic insecticide that lasts up to 22 days, can be applied every 2 to 3 weeks, and will slowly sterilize and starve the pests with slow but incredibly effective precision.