A reader reached out to me and asked why their apple tree’s leaves are curling. While I had an idea, I wanted to do more research to give them the best answer I could. Here’s what I found.
There are 6 main causes apple trees get curled leaves. Here they are, in order of likelihood:
- Under-Watering
- Extreme Heat
- Improper Nutrients
- Transplant Shock
- Pests (Aphids & Leaf Rollers)
- Diseases (Apple Scab & Fire Blight)
To fix curled leaves on apple trees, only water when the top 2-4 inches is dry, grow in USDA hardiness zones 3-8, feed it compost and fertilizer regularly, and inspect the leaves for any signs of pests or diseases such as aphids, leaf rollers, apple scab, and fire blight. Also, prune any dead or infected leaves.
So, while apple trees get curled 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. Under-Watering
The most common reason apple trees get curled leaves is a lack of water. The leaves curl as a natural response to conserve moisture. If not addressed, the leaves will continue to dry, brown, and drop from the tree. If left for too long, the apple tree can die.
You can tell if your apple tree is under-watered if its soil is bone dry. You can check this by pushing a finger into the soil, under the apple tree’s canopy.
If you feel the soil and it’s super dry, that’s likely why your apple tree’s leaves were curling.
Fortunately, under-watered apple trees are fairly easy to fix.
How to Fix Under-Watered Apple Trees
First, let’s start with when to water apple trees.
The best way to water apple trees is to only water when the top 2-4 inches of soil is dry. To check this, use the “Finger Test” by feeling the soil under the apple tree’s canopy.
By checking your apple tree’s soil before watering, you’re ensuring you avoid both under and over-watering.
Simply, if the soil is dry, water it. If it’s staying sopping wet, hold off on watering. The goal is to have soil similar to the moisture of a wrung-out sponge.
Tip: Water your apple tree to about 2 feet deep as 90% of its roots are found within this depth.
But, what happens if your apple tree’s soil is drying out too fast (in 1-3 days, or even hours)?
Compost & Mulch
- Apply 2 inches of compost every 1-2 months
- Apply 4 inches of mulch every 3-6 months
- Keep both materials under the apple tree’s canopy and at least 3 inches from the apple tree’s trunk
Two of the best practices you can do for apple trees (and most other plants) are to use compost and mulch.
Compost provides apple trees with essential nutrients, improved water retention, and healthy soil. It does this by increasing the soil’s organic matter. For example, every 1% increase in the soil’s organic matter holds an extra 20,000 gallons of water per acre.
On the other hand, mulch dramatically reduces evaporation, regulates soil temperature, and prevents soil erosion. Because apple trees evolved as understory plants in forests, they’re used to having plenty of fallen branches and leaves. As these materials decay, they increase the humus in the soil and promote healthy soil.
Mulch also has other benefits such as increasing nutrients and preventing weeds. As permaculture guru Geoff Lawton says, “A forest grows from a fallen forest.” And apple trees aren’t any different.
To recap, here’s the best way to treat under-watered apple trees:
- Only water when the top 2-4 inches of soil is dry
- Water the soil down to 2 feet
- Apply 2 inches of compost every 1-2 months
- Apply 4 inches of mulch every 3-6 months
- Keep both materials under the apple tree’s canopy and at least 3 inches from the apple tree’s trunk
Tip: Avoid mulching apple trees with poorly draining soil as it makes the issue worse by preventing evaporation. Once the drainage is amended, begin applying mulch.
But what happens if you’ve been watering and using compost and mulch, and your apple tree’s leaves are still curling and drying out?
2. Extreme Heat & Dryness
When temperatures are too dry and hot (typically 90ºF+), apple trees stop growing as they get too stressed and focus on survival. The same is true for severe cold weather, but it’s not as common due to their cold tolerance.
Apple trees that are stressed from hot and dry weather show symptoms such as:
- Curled Leaves
- Wilted or Droopy Leaves
- Dry Leaves
- Brown Leaves
- Dropped Leaves
Additionally, apple trees shed their flowers and fruit if they get too stressed. If not addressed, the apple tree dies.
The best way to avoid heat and dry stressed apple trees is to grow in their ideal climates.
The Best Climate to Grow Apple Trees
Apple trees are natively from temperate, or cooler regions, so they don’t do well in hot and dry weather. This means the best areas to grow them are USDA Hardiness Zones 3-8.
USDA hardiness zones show the average minimum temperature in an area. Knowing this helps gardeners know which plants grow best in their region. If you don’t know your hardiness zone, you can find it with this map from the USDA.
For example, zones 3-8 are usually between -40ºF and 90ºF. Any colder or hotter and apple trees will likely decline and die fairly quickly. Again, since apple trees are more cold-tolerant than they are heat-tolerant, let’s focus on how to keep your apple tree cool and prevent curled leaves.
Hot Weather Tips
First, it’s helpful to know how apple trees naturally cool themselves so we can use it to our advantage.
Apple trees (and other plants) cool themselves by sending moisture from their roots to other parts of the tree, and by exhaling moisture from their leaves. This is called transpiration, and it’s similar to how we sweat to cool ourselves.
However, when it’s too hot and dry outside, transpiration and root moisture can’t effectively keep up to cool the plant and its leaves. As a result, the apple tree’s leaves droop or curl, and then dry, brown, and drop.
Now, let’s come up with solutions to support these cooling strategies. Here are some of the best ways to keep apple trees cool:
- Temperature: The best temperature to grow apple trees is between 32ºF and 80ºF. This is because apple trees stop growing under 45ºF and 90ºF. However, apple trees require some chill hours (under 45ºF) to flower and fruit properly.
- Compost: Apply 2 inches of compost to not only provide nutrients for your apple tree but hold more water in the soil and help prevent drought stress.
- Mulch: Similar to compost, mulch goes a long way in water retention and offers other benefits such as shading and insulating the soil—regulating its temperature.
- Shade: Provide around 2 hours of shade during the hottest part of the day. The hottest hours are typically in the late afternoon from 2-4 pm (the western sun). You can do this by planting other trees or using umbrellas, structures, or shade sails.
- Density: Planting apple trees nearby other plants not only means more shade, but more transpiration from other plants. This increases the humidity in the surrounding area and helps cool apple trees. A good way to do this is with companion plants.
Many young fruit trees and other productive plants are more sensitive and usually rely on the canopies of support species such as pine, oak, and other overstory trees to survive—at least until the fruit trees are established themselves.
Because of this, provide young fruit trees with partial shade, especially from the hot afternoon, west-facing sun.
If you do live in a drier climate, and you’d like more information about the best drought-tolerant fruit trees, check out my other post: 30 Best Drought-Tolerant Fruit and Nut Trees (Ranked).
3. Improper Nutrients
Excess Nutrients
Too many nutrients are often caused by using too much of a fast-release chemical fertilizer. When this happens, the tree’s roots can become chemically burned, causing the tree stress and leading to a decline in health.
Common signs of over-fertilizing apple trees are drooping or curling leaves, discolored leaves, and dropping leaves.
If you believe you’ve over-fertilized your apple tree, I suggest removing as much of the fertilizer as possible via leaching. To do this, soak your apple tree’s soil to dilute the existing fertilizer and allow it to sink deeper into the soil (out of reach of the tree’s roots). You may have to do this at least a few times.
However, avoid leaching if your soil has poor drainage as the soil can become waterlogged. In this case, either apply generous amounts of compost and garden soil or repot the tree with fresh potting soil (for potted apple trees).
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 |
If you haven’t fed your apple tree in the past several months, there’s a good chance it’s getting curled leaves from a lack of nutrients.
The 3 main nutrients for apple trees (and all plants) are nitrogen, phosphorus, and potassium (abbreviated as NPK). Secondary nutrients such as iron, magnesium, zinc, and copper are also important and are included in most fertilizers.
For example, apple trees commonly get nitrogen and iron deficiencies, showing as lightly colored or yellow leaves. This is more likely in younger apple trees as nitrogen is the primary nutrient needed for growing a canopy.
Let’s take a look at the optimal way to prevent a lack of nutrients for your apple tree.
The Best Fertilizer for Apple Trees
Apply 2 inches of compost every 1-2 months and 1 cup of organic fertilizer for every 1 inch of the trunk’s thickness (or as directed on the back of the package).
The best fertilizers for apple trees are organic fertilizers and compost. I use a combination of both for my fruit trees, but either one can also work.
As far as when and how to fertilize apple trees, here’s what Rebecca Sideman, Sustainable Horticulture State Specialist at the University of New Hampshire, has to say.
“When fertilizing trees, apply all fertilizers evenly beneath the dripline of the branches, staying at least 18” away from the trunk. All trees should be fertilized in spring, before June 1.”
Rebecca Sideman, Sustainable Horticulture State Specialist, University of New Hampshire
When choosing an apple tree fertilizer, aim for one that has a balanced NPK, such as a 10-10-10.
If you don’t have a 10-10-10, you can supplement others if you’d like. For example, with the 6-2-4 pictured above, I also use a bit of bone meal (for phosphorus) and kelp (for potassium).
Keep in mind, young apple trees benefit from more nitrogen as it’s the nutrient required for growing. On the other hand, mature apple trees require more phosphorus and potassium as it’s helpful for flowering, fruiting, and the overall health of the tree.
I recommend using an organic fertilizer over a chemical fertilizer as it promotes healthy soil. For example, some chemical fertilizers have been found to dry out the soil and block the nutrient exchange between the apple tree’s roots and the beneficial soil life (such as earthworms and mycorrhizal fungi).
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
Alternatively, you can use compost. Apply 2 inches every 1-2 months, except for the winter as the tree is dormant.
To see which fertilizers I use and recommend for apple trees, see my recommended fertilizer page.
Soil pH
Apple trees prefer a soil pH of 5.8 to 7.0.
Apple trees need a balanced soil pH to properly dissolve the nutrients in the soil, and make them able to be absorbed by 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 test your soil’s pH are with pH strips or a meter. I prefer using a pH meter since they’re affordable and easy to use. To see which pH I recommend, check out my recommended tools page.
If you find your apple tree’s soil is too alkaline (above 7.0), provide acidic amendments such as peat moss, lime (ground limestone), and coffee grounds.
On the other hand, if your soil is acidic (under 5.8), provide alkaline amendments such as charcoal, wood ash, and lime (ground limestone).
4. Transplant Shock
If your apple tree was recently planted or repotted, and it’s starting to get curled or falling leaves, it’s likely due to transplant shock.
Transplant shock happens when a plant is exposed to a new environment and has to establish a new root system. Avoid transplanting 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 stem or trunk as before
- Apply 2 inches of compost and 4 inches of mulch to the top of the soil
- Water generously and add more soil as needed
5. Pests
Aphids
Aphids are small bugs that suck the sap from underneath the apple tree’s leaves. This loss of sugar and moisture causes the leaves to curl, discolor, and drop.
They also deposit honeydew, which attracts ants. If left unchecked, aphids can damage the apple tree’s health and potentially stunt or kill it.
These bugs come in multiple colors including white, yellow, or black, and usually hide underneath the leaves. Typically, aphids won’t cause damage to the fruit, but because they suck sap from the trees, they can compromise its health and therefore reduce fruit yields and size.
The best ways to get rid of aphids and mites on apple trees are by:
- Spraying the leaves with a jet of water
- Spraying the leaves with neem oil (a natural pesticide from the neem tree)
- Attracting ladybugs to the garden (a predator to aphids)
Most often, I’ve found a jet of water is enough to get rid of them, but neem oil is a good second option.
For example, when my potted Kaffir lime tree had aphids, I found that a jet of water was enough to blast them off and prevent them from coming back. All I did was remove the hose nozzle and used my thumb to increase the pressure. Keep in mind that too strong of a blast will damage the leaves.
Alternatively, there are even some companion plants for apple trees such as nasturtium that help keep aphids away. Others such as fennel, dill, and yarrow attract ladybugs and keep the aphids and spider mite populations down.
Leaf Rollers
Leafrollers are caterpillars that feed on apple tree leaves, flowers, and green fruit. They normally appear in the spring, when apple trees begin to bloom. The most common leafroller to infest apple trees is the Oblique-banded leafroller.
The leafroller moths lay their eggs directly on apple tree leaves, on which the caterpillars hatch and begin eating. They hatch after about 10-12 days. Similar to other caterpillars, leafrollers use webbing to curl the leaf and hide in it.
You can manage leafrollers by using pheromone traps and encouraging natural predators such as spiders. Sprays are not recommended.
Unless leafroller numbers are very high, spraying is not necessary. Repeated or unnecessary sprays will harm natural enemies that are present, such as native parasitic and predatory insects and spiders that will reduce their populations.
IPM Manual, Washington State University
6. Diseases
Apple Scab
Scab (Venturia inaequalis) is the most common disease apples, pears, and crabapple trees contract. This fungal disease primarily affects the leaves and fruit, but can also infect shoots, buds, and blossoms. Heavily infected leaves curl, turn yellow, and then brown and black as the spots grow.
These spores mainly survive and spread from diseased leaves that dropped over the winter.
Scab is most common in the warm, rainy season as water and wind allow the spores to spread. In these conditions, infections can take place as soon as 9 to 17 days. Once the infection takes hold, the fungi shoot more spores into the air. As long as the leaves are wet enough, this reproductive process will repeat.
Leaves that are infected typically drop by mid-summer. Infection over multiple seasons can weaken and kill the fruit tree.
| Location | Scab Symptoms |
|---|---|
| Leaves | 1/2 inch olive-green round spots. Heavily infected leaves turn yellow, and then brown and black. |
| Fruit | Olive-green spots that turn brown. Young fruit becomes deformed and cracked. |
How to Treat Scab
The best way to manage scab is to plant naturally resistant apple trees. Some fungicides can help manage this disease if applied at key points of infection.
Here are some best practices to treat and manage apple scab:
- Clean up infected leaves in the fall (you can burn, bury, or compost them)
- Prune the tree’s canopy to promote airflow and sunlight, reducing moisture and therefore fungal growth
- Avoid densely planting fruit trees. Keep a spacing of at least the size of a mature tree’s canopy
- Avoid fungicides on resistant or immune varieties or those already infected. Trees already infected with scab will not benefit from fungicides until the following spring. Fungicides don’t cure the tree but protect new leaves from getting infected.
- If using fungicides, apply when green leaf tips emerge in the late winter or early spring, about 1/2 inch
Fire Blight
Fire blight (Erwinia amylovora) is a highly infectious bacterial disease that affects members of the rose family—including apple, pear, and rose. This disease causes the fruit and leaves to curl, brown, blacken, and become disfigured. Sometimes, it kills the tree.
Fire blight usually spreads in the springtime when it’s warm and wet (spreading the fastest when the temperature is above 70ºF). However, during the winter, fire blight is dormant. This is why providing preventative treatment to the trees during the winter is important in handling this disease.
The bad news is that fire blight is the most common apple tree disease, and there is no cure for it.
The good news is some treatments prevent and slow the spread of fire blight. With these, fire blight is manageable and should have little to no further impact on your trees.
To see an active fire blight map of the US, check out this map on uspest.org.
To read more about this disease, see my other post: Fire Blight Treatment: Non-Organic & Organic Solutions.
If you do find your apple tree’s leaves are curling from a fungal disease, and you’re looking for a natural fungicide, check out this video by Stefan Sobkowiak – The Permaculture Orchard.
