One of our three olive trees is recently getting browning and dropping leaves. While I had an idea of what was causing it, I did some more research. Here’s what I found.
Olive trees most commonly drop their leaves from improper watering, climate, and nutrients. Less common issues are pests and diseases such as peacock spot. For best results, only water when the top 2-4 inches of soil is dry and provide compost and fertilizer.
So, while olive trees drop their leaves for several reasons, how can we tell which issue is causing it, and from there—how can we fix it? Let’s take a closer look.
1. Improper Watering
The best way to water olive trees is to only water when the top 2-4 inches of soil is dry.
I check this with the “Finger Test”, by pushing my finger into the soil, under the tree’s canopy. If the soil is wet, hold off on watering. If it’s bone dry, water it.
The goal is to have soil moisture similar to a wrung-out sponge.
The finger test is the best way to prevent both under and over-watering.
However, there are times when the olive tree’s soil is holding too little or too much moisture. In this case, we’ll need to do more than the finger test.
Under-Watering
If you check your olive tree’s soil and find it’s bone dry, the tree’s leaves are likely dropping from a lack of water.
When olive trees lack water, the roots don’t have enough moisture to send to the leaves. This causes the leaves to dry, curl, brown, and drop. Flowers and fruit also commonly drop.
Hot and dry weather makes this issue worse. If not addressed, the olive tree can quickly die.
Along with only watering when the soil is dry, here are some more tips to provide sufficient water for your olive tree:
- Provide partial shade. Olive evolved as understory trees, so they prefer the partial shade of trees. If possible, provide your olive trees with at least 2 hours of shade during the afternoon.
- Apply 2 inches of compost. Compost increases the organic matter of the soil. Every 1% increase in the soil’s organic matter leads to an additional 20,000 gallons of water held per acre.
- Apply 4 inches of mulch. Mulch keeps the soil covered, providing essential protection from the sun, wind, and erosion. It also feeds earthworms, mycorrhizal fungi, and the like, which provide many benefits to plants (more on these later).
Recommended: The Top 30 Drought-Tolerant Fruit Trees (Ranked)
Over-Watering
On the other hand, if your olive’s soil is sopping wet for 1-2 days or more, its dropping leaves are most likely from over-watering.
Over-watering occurs from providing too much and too frequent water, but the more common cause is soil with poor drainage.
Let’s take a look at how to test your olive tree’s drainage, and how to amend it if needed.
How to Test Soil Drainage
The best way that I’ve found to test soil drainage is by doing a percolation test near the tree (outside its drip line or canopy).
Here’s how to do a percolation test:
- Dig a 1-foot by 1-foot hole
- Place a yardstick in the hole and fill it with water
- Wait an hour and measure how far the water has drained
Ideally, soil drainage should be around 2 inches per hour. But this is a guideline and not a rule, so don’t worry if yours is way off. For example, I did 3 different percolation tests across my yard and found drainage up to 5 inches per hour.
How to Amend Soil Drainage
If you find your soil is draining too fast or slow, the solution is the same. Apply compost!
Adding organic matter to the soil not only increases its water retention but also breaks up the larger clumps of soil.
I recommend applying 2 inches of compost every 1-2 months. Simply place the compost on top of the soil, under the olive’s drip line. Over time, the compost will work its way into the soil. With assistance from the plant’s roots and the soil life, even heavy clay soil will be amended.
If you’d like faster results, you can also use sand or perlite to break up the clay.
Limit chemical amendments such as gypsum as it can mess with the structure of the soil and affect crop yields.
“Improving water infiltration can be best achieved by limiting tillage to leave the most crop residue as possible rather than applying gypsum.”
J.E. Sawyer and D.W. Barker, Department of Agronomy, Iowa State University
So, avoid digging excessively or tilling the soil. This gives the beneficial soil life a chance to grow and support the olive tree. Of course, if your olive tree is waterlogged where it’s at, it’s probably a good idea to move it.
Lastly, avoid mulching soil with poor drainage as it prevents evaporation and makes the issue worse. Once the soil is well-draining, apply 4 inches of mulch every 3-6 months for benefits such as reduced evaporation, regulated soil temperature, and less weed growth.
Recommended: 10 Expert Tips for Watering Fruit Trees
2. Extreme Weather
For best results, grow olive trees in USDA hardiness zones 9-11. This is generally between 25ºF and 90ºF. While they can grow in zone 8, a harsh freeze will easily kill them.
Even though olive trees can tolerate temperatures slightly above and below these ranges, this guideline gives them a better chance to grow and avoid losing leaves (among other issues).
Recommended: How to Find The Best Fruit Trees For Your Climate
Also, keep in mind that olive trees are evergreen, so they keep their leaves year-round. If your olive tree is losing a large number of leaves (20% or above), and you’ve had unusual weather, it’s likely causing the issue.
Let’s take a look at the climates that olive trees prefer.
Too Hot
As olive trees are native to the Mediterranean, they generally do best in drier climates. However, some varieties do well in wetter or cooler areas.
When olive trees are exposed to temperatures of 95ºF and above for extended periods, their leaves get too hot which stresses the plant and hinders the growth of leaves and fruit.
In this case, the plant can’t send moisture from its roots to its leaves fast enough, which causes the leaves to dry, droop, curl, brown, and drop.
Here are some ways to keep your olive tree cool:
- Provide 2 inches of compost for water retention
- Apply 4 inches of mulch for insulation
- Provide at least 2 hours of partial shade in the afternoon. You can use shade sails, structures, or other trees.
Too Cold
As olive trees prefer warmer and drier climates, they are fairly vulnerable to frost. As a result, avoid exposing your olive trees to temperatures under 32ºF if possible.
Here are some tips if temperatures fall below your olive tree’s minimum temperature:
- Provide 4-12 inches of mulch for insulation
- Wrap the canopy with a bedsheet to reduce windchill and ice buildup
- Wrap the trunk with cardboard or another insulating material
- Bring potted olive trees inside, but away from the central heat as it dries out the leaves (this happened to my potted Meyer lemon tree)
But, what happens if your watering and weather check out?
Not Enough Sunlight
As with most fruit trees, olive trees require at least 6 hours of direct sunlight a day. While some olive trees can grow with as little as 4 hours per day, you’ll often see reduced growth and dropped leaves the fewer hours the plant receives.
Sunlight is critical for plant and fruit growth as it encourages photosynthesis, providing necessary energy and sugars for the plant.
Here are some tips to boost the sunlight for your olive tree:
- Plant on the south side of your property for maximum sunlight (if you live in the southern hemisphere, this is the north side).
- Place the tree near a south-facing wall to allow heat and sunlight to reflect onto the tree (you’ll likely need to provide it with more water than usual)
- Prune any trees above the olive tree to allow for more sunlight. You can also prune the olive tree’s excess and overlapping branches to increase sunlight and airflow into the canopy (and reduce pest and disease exposure).
Recommended: 10 Expert Tips to Prune Fruit Trees
If your olive tree’s leaves are curling or browning, it’s likely a sign the tree is getting too hot and could use some shade from the afternoon sun.
In this case, use the shade from other trees, structures, or items such as shade sails. 2+ hours of daily, partial shade from the western sun will work.
3. Improper Nutrients
Excess Nutrients
Excess nutrients (over-fertilizing) chemically burn the olive tree’s roots, causing stress and leading to poor growth as well as decreased flowering and fruiting. Normally, fast-release chemical fertilizers are the cause of over-fertilization as organic fertilizers and compost aren’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 |
| Zinc | Yellow blotches |
| Manganese | Broadly pale leaves, foliage color looks mottled or smeared |
A lack of nutrients also stresses olive trees, leading to conditions such as stunted growth and dropping leaves and fruit. This is commonly caused by poor soils, leaching, and other conditions such as improper pH.
Nutrient leaching occurs when the olive tree is over-watered or has too much drainage (common with sandy soils). This causes the nutrients to seep too deep into the soil, out of reach of the plant’s roots, which are about 2-3 feet deep.
Fortunately, most of these issues can be resolved by properly fertilizing olive trees.
The Best Way To Fertilize Olive Trees
Olive trees (and most plants) require three main nutrients.
- Nitrogen (N): The most important nutrient, vital for canopy and root growth.
- Phosphorus (P): Essential for flowering and fruiting
- Potassium (K): Maintains the overall health of the tree
Generally, olive trees prefer a balance of all three nutrients. When shopping for fertilizer, aim for one that says something similar to 10-10-10 NPK (the percentage of nitrogen, phosphorus, and potassium). The closer you can get to a balanced figure the better.
There are also a few different kinds of fertilizers you can use:
| Chemical Fertilizers | Organic Fertilizers | Compost |
|---|---|---|
| Quantity > Quality | Quality & Quantity | Quality & Quantity |
| Can dry soil | Great for soil | Great for soil |
| Can damage soil | Not as fresh as compost | Great for water retention |
Even though chemical fertilizers might be sufficient over the short term, over the long term they often short-circuit the nutrient exchange between the tree and its beneficial soil life (such as mycorrhizal fungi). This leads to dry and dead soil (AKA dirt) and overall decreased plant health.
Mycorrhizal fungi promote many aspects of plant life, in particular improved nutrition, better growth, stress tolerance, and disease resistance.
Department of Biology, University of Fribourg, Switzerland
For my olive trees, I use both organic fertilizer and compost. I find that organic fertilizer provides significant nutrients while compost fills any gaps in the nutrient profile and amends the soil.
Compost provides more than sufficient nutrients, increases water retention, and promotes healthy soils. Many gardeners are even finding that compost is replacing their fertilizers.
If you choose to use compost, select one with the highest quality and freshness if possible as its beneficial organisms will still be alive.
Either one you choose—you can see my recommendations for both compost and fertilizer on my recommend fertilizer page.
Soil pH
While most other fruit trees prefer a soil pH of 6.0 to 7.0, olive trees are hardier and do well with a soil pH between 5.0 to 8.5.
Nutrients are essential, but they’re next to useless if the soil does not have a proper pH. This is because a slightly acidic pH is necessary to dissolve the nutrient solids in the soil and make them accessible for the plant’s finer roots.
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 olive tree’s soil is too alkaline (above 8.5) you can add acidic amendments such as coffee grounds, sand, and peat moss. On the other hand, if your olive tree’s soil is too acidic (below 5.0), add alkaline materials such as wood ash, charcoal, or lime (ground limestone).
Additionally, cold and/or wet soils are not good at promoting nutrient uptake as the olive tree will either be dormant during the cold or too stressed in wet soils.
4. Transplant Shock
If your olive tree was recently planted or repotted, and it’s dropping its leaves, it’s likely due to transplant shock. Transplant shock occurs when a plant is exposed to a new environment and has to establish a new root system.
Avoid transplanting olive trees unless necessary as it can take up to 1 year for recovery.
To help avoid transplant shock, I like to plant with the following steps in mind:
- Have the new ground (or pot) prepared
- Remove as much of the plant’s current topsoil as possible, without damaging the shallow roots
- Grab the base of the plant’s stem and wiggle lightly
- Using your other hand, scoop up and support the rootball
- Lightly place the plant in the new ground (or pot) and fill it in
- Make sure the soil is at the same level on the plant as before
- Apply 2 inches of compost and 4-12 inches of mulch to the top of the soil
- Water generously and add more soil as needed
5. Pests and Diseases
Root Rot
Root rot kills off the olive tree roots, which stresses the plant and causes symptoms such as fruit, flowers, and leaves yellowing, browning, and dropping. If not addressed, it leads to stunted growth or a dying olive tree.
You can typically tell if your olive tree has root rot if the soil is staying sopping wet and starts smelling. Allowing the soil to dry out or repotting olive trees with fresh potting soil are the best ways to amend this disease.
For example, I noticed my potted Kaffir lime tree had root rot as its soil smelled swampy and was staying wet for many days at a time. In this case, I repotted it with fresh potting soil, and the tree quickly recovered.
Verticillium Wilt
Verticillium wilt is a fungus that is similar to root rot in that it usually occurs in soils with excess water. Additionally, over-fertilizing can also cause it.
The most susceptible fruit crops that contract verticillium wilt are nightshade (tomatoes, peppers, and eggplants), but other fruiting plants such as olive trees can also be infected. Symptoms of this disease include leaves wilting, yellowing, and dropping, and potentially branch dieback.
Prevent and treat verticillium wilt by pruning infected branches, avoiding excess water and fertilizers, and following best gardening practices.
Peacock Spot
While the above conditions lead to brown leaves, if your olive tree’s leaves have yellow, brown, or black spots it’s likely peacock spot disease.
Peacock spot (Spilocaea oleaginea) is a fungal disease that causes olive tree leaves to get brown and black spots with yellow rings around the spots. After some time, the leaves drop from the tree. The tree’s flowers, fruit, and growth are also affected.
This disease is most common in the fall when it’s warm and wet, and is usually found in coastal climates.
Treatment typically involves a spray. To learn more about which sprays are recommended for peacock spot, contact your local cooperative extension office.
Alternatively, Stefan Sobkowiak – The Permaculture Orchard has a great video on a safe, homemade, and more importantly—effective fungicide (hint: the secret ingredient is whey). You can see his video below.
Final Thoughts
After some trial and error, we found our olive tree’s dropped leaves were from under-watering. After we set up the more regular drip irrigation and provided compost and mulch, it made a quick recovery!
For your olive tree, I suggest starting with watering (the finger test) before moving on to other issues such as climate, nutrients, and diseases. Typically, in that order. I try to save the most invasive option for last (transplanting or repotting), as it causes the tree the most stress.
