A reader recently asked if I knew why their apple tree’s leaves were curling. While I have experience with curled leaves on other fruit trees, I couldn’t find much information on apple tree leaves curling. So, I did some research. Here’s what I found.
Apple trees get curling leaves from under-watering, hot weather, improper nutrients, transplant shock, and pests and diseases such as aphids and blight. Ideally, only water apple trees when their soil is dry, apply compost and mulch, and provide partial shade from the heat if needed.
So, while apple trees get curling leaves from several possible issues, how can we tell which one is causing it, and from there—how can we fix it? Let’s take a closer look.
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Apple trees that are lacking water quickly get issues such as leaves curling, browning, and dropping. The reason why leaves curl when they’re drying is to conserve moisture and if they’re left without water for too long, they’ll begin to brown (die) and drop from the tree.
Under-watering is easy to do as it’s difficult to tell how much moisture the soil is holding, especially deeper in the soil. This is made worse if you’re experiencing excessively hot weather or times of drought (more on these later).
So, what’s the ideal way 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, push a finger into the soil under the tree’s canopy. The goal is to have soil similar to the moisture of a wrung-out sponge. This practice prevents both under and over-watering.
Make sure your apple tree’s soil is thoroughly watered to about 2 feet deep as 90% of its roots are found within this depth.
Additionally, applying compost and mulch goes a long way in helping your apple tree retain water and become more water independent.
Compost not only provides valuable nutrients but improves water retention and the soil’s richness. For example, every 1% increase in the soil’s richness can hold an extra 20,000 gallons of water per acre (source).
Mulch dramatically reduces evaporation, regulates soil temperature, and prevents soil erosion. It’s also key for fruit trees as mulch mimics a forest’s ground cover—providing many of the above benefits and feeding the fruit trees.
Provide your apple tree with 2 inches of compost and 4-12 inches of mulch. When applying, keep these materials at least 3 inches away from the apple tree’s trunk to prevent mold. Reapply compost every 1-2 months and mulch every 3-6 months.
So, along with only watering your apple tree when its soil is dry, provide it with compost and mulch for best results.
But what if your apple tree’s soil feels like a wrung-out sponge, but its leaves are still curling? What should we check next?
2. Extreme Heat
Apple trees grow best in USDA hardiness zones 3-8, but there are some warmer and colder apple varieties that survive outside this range (source). Generally, avoid exposing your apple tree to temperatures above 85ºF if possible.
In hot and dry climates, apple trees lose moisture from their leaves and soil quickly. Normally, apple trees cool themselves by sending moisture from their roots to their leaves, and through transpiration.
Much like humans, plants breathe and release moisture when hot. For plants, this is called transpiration. But when the climate is too hot and dry, 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.
So, the hotter and drier the weather, the more energy the plant uses to transpire and survive, and the less energy it has to use to establish its root system and grow. This drain of resources can quickly stunt or kill the plant.
Hot Weather Tips
Here are some tips that will help your apple tree survive warmer weather and the occasional heat spell:
- 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, but also offers other benefits such as shading and insulating the soil—regulating its temperature.
- Shade – partial shade further protects the tree’s leaves, roots, and soil from the heat. Some ideas to create shade for your apple trees are to use large umbrellas, shade sails, trellises, or other trees.
Many young fruit trees and other productive plants are more sensitive and usually rely on the canopies of support species such as pine trees and other overstory trees to survive—at least until the fruit trees are established themselves.
Because of this, provide any young fruit trees with partial shade, especially from the hot afternoon, west-facing sun. Once the fruit trees mature and develop a larger canopy and root system, they’ll be able to access and hold more groundwater and have a better chance of surviving on their own.
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
Apple trees that are over or under-fertilized become stressed, leading to curling and browning leaves. A lack of nutrients causes deficiencies while nutrient potency from excess fertilizer causes the apple tree’s roots to burn.
For best results, use a quality fertilizer as directed, or 2 inches of compost every 1-2 months.
Chemical Fertilizers vs Compost
While chemical fertilizers have nutrients in quantity, they typically lack nutrients in quality. This can cause stress for the apple trees as they’re unable to absorb sufficient nutrients. Additionally, much of the nutrients from chemical fertilizers are often leached through the soil when watering.
Chemical fertilizers can also have other, unintended consequences, such as killing beneficial soil life and drying out the soil.
Fortunately, compost and manure have been found to contain more than sufficient nutrients for plants (including apple trees).
Approximately 70-80% of nitrogen (N), 60-85% of phosphorus (P), and 80-90% of potassium (K) found in feeds is excreted in the manure. These nutrients can replace fertilizer needed for pasture or crop growth, eliminating the need to purchase fertilizers.University of Massachusetts Amherst
Compost also feeds beneficial soil life such as earthworms and mycorrhizal fungi, leading to benefits such as improved soil aeration, nutrient availability, and disease resistance.
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
If you’re interested to learn more, feel free to check out my other post: Can Compost Replace Fertilizer? Here’s What the Experts Say.
Keep in mind that nutrients aren’t everything—apple trees also need a specific soil pH to properly absorb nutrients and thrive.
Apple trees prefer a soil pH of 5.8 to 7.0.
This is important because an acidic soil pH dissolves the solid nutrients in the soil, and makes them available 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, SUNY College of Environmental Science and Forestry
Two good ways to check the soil’s pH are with pH strips or a pH meter. I prefer using a meter since they’re affordable and easy to use. To see which pH meter I use and recommend, view my recommended tools page.
4. Transplant Shock
If an apple tree was recently planted or repotted, and it’s starting to die, it’s probably due to transplant shock. Transplant shock occurs when the 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.
Like many plants, apple trees are vulnerable to transplant shock, which can take up to a year for them to recover from. 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
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 infected leaves with water or neem oil, or releasing ladybugs (a natural predator of aphids and mites). Most often, 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.
Tent caterpillars are native to North America and typically hatch around March—the time that apple trees start to blossom. They’re commonly found on apple, crab apple, cherry, hawthorn, maple, peach, pear, and plum trees. Insecticides are largely ineffective, but parasitic wasps will help reduce their numbers.
These caterpillars eat the apple tree’s leaves, make silken nests, and can quickly overwhelm the tree in numbers. The leaves have been seen to be eaten partially (leading to brown and dropping leaves) or entirely. Some trees can be nearly defoliated. However, the tree usually grows new leaves the following season.
While insecticides typically won’t work with mature larvae, promoting natural predators such as parasitic wasps and removing eggs from trees in the winter brings the best results (source).
Fire blight (Erwinia amylovora) is a highly infectious bacterial disease that affects members of the rose family—including apple, pear, crabapple, rose, cotoneaster, mountain ash, hawthorn, quince, spirea, and pyracantha. Fire blight causes the fruit and leaves to curl, brown, blacken, and become disfigured. Sometimes it will kill the tree.
This disease spreads most often 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 (source).
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.
Also, to read more about this disease, feel free to visit my other post: Fire Blight Treatment: Non-Organic & Organic Solutions.
Generally, young and budding plants are the most vulnerable to diseases and apple trees aren’t any different.
Budding apple trees occasionally get a fungal disease called rust. This disease affects apple tree leaves, flowers, and fruit and causes them to become discolored and disfigured. It’s common for apple trees to shed heavily infected leaves in the summer. Typically rust is caused by nearby cedar (juniper) trees.
In regards to management, some recommend removing all cedar and juniper trees within 1/4 mile or more, which isn’t feasible for most growers. However, there are other methods of prevention.
- Preventative organic sprays*
- Growing resistant varieties
*Keep in mind that some sprays mean the tree’s fruit cannot be eaten that season.
If you’d like the most accurate details on the different conditions apple trees get in your region (and how to treat them), I recommend reaching out to your local nursery, professional orchard, or local extension service.
More Tips to Care for Apple Trees
- If your apple tree’s leaves are curling due to hot or dry weather, provide 1-2 hours of shade during the hottest part of the day (along with mulching and deep watering). The hottest hours are typically in the late afternoon from 2-4 pm.
- Use mulches such as fallen leaves, bark, or pine needles. However, pine needles can be more acidic than the others, so make sure to check the soil’s pH every month or two.
- Amend clay soil with sand and compost. The sand will not only break up the clumps of clay but also increase the acidity of the soil. Adding compost will help prevent the sand from creating too much drainage and support proper water retention in the soil.