A reader recently reached out to me and asked why their mulberry tree might be dropping leaves. While it’s a bit tricky to tell from a photo, I did some research to find out more. Here’s what I found.
Mulberry trees drop their leaves naturally in the fall and winter, being deciduous trees. But if they drop their leaves in the spring and summer it’s likely due to improper watering, climate, nutrients, or pests and disease. For best results, only water mulberry trees when the soil is dry and provide compost and mulch.
While these are some of the reasons why mulberry trees drop leaves, how can we tell which issue is causing it, and from there—how can we fix it? Let’s take a closer look.
1. Seasonal
Mulberry trees are deciduous, so their leaves normally turn yellow and brown, and drop in the fall.
The reason behind this is that deciduous trees enter a state of dormancy during the colder weather (similar to bears hibernating). As a result, they shed their leaves to ensure they don’t waste resources keeping them alive during the winter.
On the other hand, evergreen trees generally keep their leaves year-round (until an individual leaf gets old or develops an issue such as dryness). Citrus trees are a good example as they evolved in the tropics, where there’s little to no frost. Because of this, they didn’t need to adopt a dormancy response.
Some evergreen trees can survive cold weather through other measures. For example, professional German forester Peter Wohlleben, in his book The Hidden Life of Trees, shows that pine trees have a naturally occurring antifreeze that allows them to keep their needles during cold weather.
So, if your mulberry tree is losing leaves in the fall and winter know that it’s completely normal!
But what if your mulberry tree is losing leaves in the spring and summer? What should we check next?
2. Improper Watering
When mulberry trees either have too little or too much water, their leaves begin to drop. This is a result of stress from drought or waterlogged soil.
Common symptoms of too little water are leaves curling, drying, browning, and dropping. With too much water, the mulberry’s leaves can drop while they’re green.
The best way to water mulberry trees is by only watering when the top 2-4 inches of soil is dry. You can check this by pushing a finger into the soil. The goal should be moisture similar to a wrung-out sponge.
When watering, make sure to soak the soil down to 2 feet as over 90% of the tree’s roots are found at this depth.
Additionally, apply 2 inches of compost and 4-12 inches of mulch.
Compost provides valuable nutrients and improves the richness of the soil. With every 1% increase in the soil’s richness, it can hold an additional 20,000 gallons of water per acre (source). Compost also promotes beneficial microorganisms including 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
Mulch greatly reduces evaporation, regulates soil temperature, and prevents soil erosion. As Permaculture guru Geoff Lawton says, “A forest grows from a fallen forest.” So, mimic the fallen leaves and branches from a forest by providing plenty of mulch for your mulberry trees!
While it can seem like a lot, by following the above tips you’ll prevent the majority of watering issues with your mulberry tree.
3. Extreme Weather
Even if you’re watering your mulberry tree properly, an extreme climate can still cause its leaves to drop.
Since mulberry trees are deciduous and fairly cold hardy, surviving down to -20ºF (USDA zones 4-8), it’s more likely they’ll get leaves dropping from excess heat. Generally, this is above 90ºF.
The only issue I can see mulberry trees having with their leaves in the winter is if they come out of dormancy (above 45ºF) and think it’s spring. If they start growing leaves and get a late frost (under 32ºF), it would likely damage the leaves and blossoms, stunting the tree until the following year.
Because this isn’t as likely, we’ll focus on how to deal with heat stress.
Tips for Hot Weather
- Compost and mulch – as mentioned earlier, compost and mulch are incredibly effective practices for keeping mulberry trees properly watered and cool. As long as the soil is staying moist and is not sopping wet, the tree can cool and support its leaves.
- Partial shade – using other trees or structures to provide partial shade for mulberries mimics their natural environment and gives them a break from the hot sun. Generally, the best direction to provide relief is the western sun. Even 2 hours of shade goes a long way.
- Dense planting – by densely planting mulberries with other plants, more roots hold groundwater, more canopies provide shade, and more leaves increase moisture (through transpiration). So, not only does the ground stay cool and moist, but the air as well! Densely planting different species also provides many companion plant benefits.
4. Improper Nutrients
Excess Nutrients
Too many nutrients are often caused by fast-release chemical fertilizers as compost isn’t potent enough. When this happens, the tree’s roots can become chemically burned, causing the tree stress and leading to leaf drop.
If you believe you’ve over-fertilized your mulberry tree, I suggest removing as much of the fertilizer as possible via leaching. To do this, provide your mulberry tree with plenty of water to dilute the existing fertilizer and allow it to flow deeper into the soil (out of reach of the tree’s roots).
However, avoid leaching if your soil has poor drainage. In this case, either apply generous amounts of compost and garden soil or repot the tree with fresh potting soil (for potted mulberries).
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 mulberry tree in the past few months, there’s a good chance its leaves are dropping from a lack of nutrients.
Although, the exact symptoms depend on the deficiency. For example, mulberry trees commonly get a nitrogen deficiency and get lightly colored or yellow leaves. This is more likely in younger mulberry trees as nitrogen is the primary nutrient needed for growing a canopy.
Let’s take a look at the optimal way to fertilize mulberry trees.
The Best Way To Fertilize Mulberry Trees
If you decide to use a chemical fertilizer, opt for one with a balanced NPK (nitrogen, phosphorus, and potassium) such as a 10-10-10. Each brand has different potencies, so follow the instructions on the label for the best results.
Alternatively, it’s difficult to over-apply compost. I recommend applying 2 inches of compost every 1-2 months under the tree’s drip-line (canopy). Applying mulch on top of the compost makes it go a lot further and adds to the water retention and nutrients.
Generally, I prefer using compost, and many gardeners are finding that compost replaces their chemical fertilizers.
Either one you choose, if you’d like to see which fertilizers and compost I recommend, check out my recommended fertilizer page.
While nutrients are essential, they aren’t everything.
Imbalanced Soil pH
When mulberry trees have an imbalanced soil pH, they can develop issues such as discolored and dropping leaves. Additionally, their flowers and fruit can drop early.
Mulberry trees prefer a soil pH of 5.5 to 6.5 (source).
The reason mulberries (and most plants) prefer a slightly acidic soil pH is because it helps dissolve the nutrient solids in the soil, making them more accessible to 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 mulberry tree’s soil is too alkaline (above 7.0), provide acidic amendments such as peat moss, sand, and coffee grounds.
On the other hand, if your soil is acidic (under 5.5), provide alkaline amendments such as charcoal, wood ash, and lime.
5. Pests and Diseases
Mulberry Leaf Spot
Leaf spot is a fungal disease (Mycosphaerella mori) that typically affects white and black mulberries, causing leaves to become spotted, yellow, brown, and black. Infected leaves can also drop from the tree. As a result, the tree’s fruit yield weakens.
Best practices for leaf spot are to collect and burn any leaves in the autumn (after the leaves have dropped) and to provide proper water and nutrients.
There aren’t many treatments for leaf spot as fungicides aren’t effective once the leaves have been infected. Additionally, the fruit becomes inedible after spraying (source).
Root Rot
Root rot, also called Phytophthora Root & Crown Rot, is a root fungus that causes mulberry tree leaves, blossoms, and fruit to droop, yellow, brown, and drop.
This disease typically occurs in areas with poor drainage. To prevent and treat root rot, promote well-draining soils and transplant young trees with fresh soil if necessary. Raised beds are also helpful in improving soil drainage.
There is no chemical control available for crown and root rot in the home garden. The most important control strategy is careful water management.
Clemson University Cooperative Extension Service
My potted Kaffir lime tree had root rot recently, which I was able to tell based on the sopping wet soil and swampy smell. Fortunately, after repotting the tree with fresh potting soil and waiting a few days, the tree made a full recovery!
Leaf Scorch
Leaf scorch is a bacterial disease (Xyllela fastidiosa) that causes mulberry leaves to yellow, brown, and drop. Occasionally, entire branches and even the tree can die. You can tell if your mulberry tree has leaf scorch due to its burned, or scorched appearance.
This disease usually occurs in the summer and is transmitted by insects such as leafhoppers and spittlebugs (source1, source2).
As of the time of this writing, there are no known treatments for leaf scorch. However, it can be prevented by keeping the tree healthy through proper watering and nutrient practices.
A Note on Pesticides and Fungicides
My parents recently had an issue with caterpillars eating their basil plants and they were about FED UP. Every time they’d plant basil, 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.
