We have a large lime tree and while it was doing well at one point, it started to fall over onto our fence. So, after some heavy pruning, it started standing on its own again. However, almost every single leaf turned yellow and fell off. Not sure what to do, I took to the web in search of answers. Here’s what I found.
Lime tree leaves turn yellow from over-watering, improper nutrients, lack of sunlight, and pests and diseases. However, the most common issues are over-watering and improper nutrients. For best results, only water when the soil is dry and apply 2 inches of compost and 4-12 inches of mulch.
While lime tree leaves turn yellow for several reasons, how can we tell which issue is causing it, and how can we fix it? Let’s take a closer look.
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The most common reason why lime trees get yellow leaves is stress from over-watering. This is especially common in soils with poor drainage.
Over time, waterlogged soil can develop mold and lead to root rot (also called Phytophthora root and crown root). Root rot slowly decays the lime tree’s roots, turning the leaves yellow, and over time, can kill the plant.
So, what’s the optimal way to water lime trees?
The best way to water lime trees is to only water when the top 2-4 inches of soil is dry. You can check this by pushing a finger into the soil. Water until the soil is saturated down to 2 feet deep. Additionally, provide 2 inches of compost and 4 inches of mulch such as leaves, bark, straw, or pine needles.
By watering the soil down to 2 feet, you’re providing 90% of the lime tree’s roots with water.
Also, by only watering when the soil is dry, you’re preventing both under-watering and over-watering. This helps the plant establish water independence.
Lime trees that are watered with frequent and light watering typically only grow extremely shallow roots. After all, why would they grow deeper roots if the water and nutrients are only on the surface?
This keeps the plant at a disadvantage as their shallow roots mean they’re poorly prepared for windy weather and droughts.
So, if you want your lime tree to be more self-sufficient and have a better chance of surviving the occasional drought, water it only when the soil is dry and down to 2 feet deep.
However, soils that have poor drainage (common with clay soils) can complicate this process.
Generally, planted lime trees are hard to amend as there are large volumes of soil (needing large amounts of amendments). Because of this, the best way to amend garden soil for better drainage is to apply 2 inches of compost on top of the soil every 1-2 months. Over time, the smaller particles will work their way into the deeper soil. Avoid excessive mulching at this time it can further lock in the moisture.
On the other hand, potted lime trees with poor drainage can be amended fairly quickly by repotting them with fresh potting soil. This is what worked when my Kaffir lime tree had poor drainage and root rot. Since the tree’s roots are limited to the pot, they generally don’t get as much transplant shock as digging up planted trees with spread-out and established roots.
But, what if we’re watering our lime trees correctly? What do we check next?
2. Improper Nutrients
Excess nutrients are typically caused by over-fertilizing lime trees. This can lead to the potential burning of the lime tree’s roots, causing the plant stress and developing yellow leaves. Normally, fast-release fertilizers are the cause of over-fertilization as compost isn’t potent enough.
Lack of Nutrients
|Nutrient Deficiency||Leaf Symptom|
|Nitrogen||Entire leaf is pale or yellow|
|Iron||Dark green veins, rest of the leaf is yellowing|
|Manganese||Broadly pale leaves, foliage color looks mottled or smeared|
A lack of nutrients also stresses the lime tree, which then develops yellow leaves. Insufficient nutrients are commonly caused by poor soils, leaching, and other stressors. Nutrient leaching is when soils have too much drainage or are over-watered and the nutrients seep too far down into the soil, out of reach of the plant’s roots.
The Best Way to Fertilize Lime Trees
You can choose to fertilize your lime tree soil with fertilizer or compost.
Generally, while chemical fertilizers have nutrients in quantity, compost has quality nutrients. What this means is that over the short term, chemical fertilizers can out-perform compost, but over the long term, they often cause soil damage. This damage leads to dry soil and decreased pest and disease resistance.
On the other hand, compost provides more than sufficient nutrients, increases water retention, and promotes healthy soils. For example, every 1% increase in the soil’s richness (organic matter) leads to 20,000 more gallons of water absorbed per acre (source).
Either way you go, if you’d like to see which fertilizers I recommend, check out my recommend fertilizer page.
Aside from nutrients, keep in mind that lime trees need a balanced soil pH between 6.0 to 7.0 (source).
The reason why lime trees prefer soil with a slightly acidic pH is because it’s ideal to dissolve nutrients in the soil.
Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils.Donald Bickelhaupt, Instructional Support Specialist, Department of Forest and Natural Resources Management
Two good ways to check your soil’s pH are either by using a pH strip or a pH meter. I prefer using a pH meter since they’re affordable and easy to use. To see which pH meter I use and recommend, check out my recommended tools page.
If you find that your lime tree’s soil is too alkaline (above 7.0) you can add acidic amendments such as coffee grounds, sand, and peat moss. On the other hand, if your lime tree’s soil is too acidic (below 6.0), add alkaline materials such as wood ash, charcoal, or lime.
Additionally, cold and/or wet soils are not good at promoting nutrient uptake as the lime tree will either be slightly dormant during the cold or too stressed in wet soils.
If you’re growing your lime tree in a container, aim to have at least a 5-gallon pot as the lime tree’s roots need a bit of room to spread.
3. Lack of Sunlight
Lime trees generally require at least 6 hours of sunlight to photosynthesize properly. Without it, their leaves turn yellow and they’re unable to develop sugars for the plant. Over time, this low energy leads to the plant’s declining health, which can potentially die.
Tips to Increase Sunlight
- Plant the lime tree in a south-facing direction for maximum sunlight (north-facing if you live in the southern hemisphere)
- Plant the tree along a south-facing wall to reflect more sunlight and heat onto the tree (some heat even persists into the night).
- Prune some overstory trees that are blocking the lime tree’s canopy from the sun. You can also prune the lime tree itself to allow more light to reach the mid and lower branches. This new space also increases aeration from the sun and wind—discouraging disease from spreading.
If your lime tree’s leaves are yellowing or dropping, there’s a chance it might have whiteflies.
Whiteflies are small white bugs that look like flies (hence the name) and are closely related to aphids. They can be found in clusters underneath leaves and are typically found in warmer climates. Whiteflies feed on leaves which results in a sticky honeydew, which can introduce fungus to your lime tree (source).
If the whitefly population gets too large, they can feed on too many leaves, which results in a weak lime tree unable to properly photosynthesize. When this happens, the leaves turn yellow and fall off.
Most times, simply hosing your lime tree leaves with good pressured water can knock them off (I’ve done this with aphids and it worked well).
Other times, hosing whiteflies with water won’t work. In these cases, spraying soapy water will remove them and bind their wings and movement, which quickly prevents them from feeding. From there, they’ll soon die off.
Aphids are a common occurrence in most gardens and you’ll likely have to deal with them at one point or another. Like whiteflies, they suck nutrients from plants and can weaken the plant, causing leaves to yellow and drop.
They can range in a variety of colors, but the best way to identify them is to check under leaves. They can sometimes be too small to see, but their clusters can be fairly obvious. If you see wilting, yellowing, or damage to your lime tree’s leaves, try checking underneath them for clusters of white, black, or yellow dots.
Just like whiteflies, aphids can commonly be controlled by using a jet of water or a soapy spray. You can also use neem oil or ladybugs (a natural predator to aphids). You can get neem oil and ladybugs from most garden supply stores or nurseries.
I’ve had aphids on my kaffir lime tree before, and by using a hose (without a spray attachment) and covering the opening with my thumb, it was enough to create pressure to knock them off. They haven’t come back since.
Root rot can occur on your lime tree when a fungus known as Phytophthora inhabits your lime tree’s soil. It can be caused by overwatering, excessive rainfall, or when bacteria travel from elsewhere through splashed dirt. However, most of the time root rot is caused by overwatering and poor soil drainage.
As a side-effect, root rot can cause your lime tree’s leaves to turn yellow and fall off, so it’s important to act fast when you see these signs show up on your lime tree. You can treat root rot by repotting your lime tree and adjusting your watering amount and schedule appropriately.
Alternaria is a fungal disease that can affect your lime trees’ young leaves. This disease can cause brown and yellow spots on your lime tree, so it’s important to keep an eye out for these signs.
To avoid Alternaria, make sure your trees have the appropriate spacing they need to thrive and grow. Giving your lime tree the space it needs from the start is key to avoiding diseases like Alternaria from forming later on.
A Note on Pesticides, Fungicides, and Herbicides
My parents recently had an issue with caterpillars eating their basil plants in Ventura, CA, and they were about FED UP. Every time they’d plant basil plants, the caterpillars ate it.
Fortunately, instead of giving into chemical sprays, they found an organic spray at their local nursery that’s made from fermented rum. The day after spraying, they’d find dead caterpillars on the soil.
If you’d like to find out more about this organic spray, you can find it here on Amazon.
So, what’s my point here?
Even though chemical sprays and fertilizers are an easy way out, like all easy and convenient things, there are usually long-term costs. Namely to the plants, soil, and surrounding beneficial life. Before using chemical sprays, weigh the pros and cons and consider trying organic or permaculture-based treatments first!
To give you a head start, Stefan Sobkowiak – The Permaculture Orchard has a great video on a safe, homemade, and more importantly—effective fungicide (hint: the secret ingredient is whey).
Also, check out how Mark Shepard uses a method called STUN (Sheer-Total-Utter-Neglect) to help his berries, fruit, and nut trees THRIVE.