I’ve been researching mulberry trees recently and a common issue I’ve found is their leaves turning brown. While I found some information out there, I wasn’t able to find a great answer. So, I did some more digging. Here’s what I found.
Mulberry trees are deciduous, so they normally get brown leaves and drop them in the fall and winter. However, if they’re getting brown leaves in the spring or summer, it’s likely due to under-watering, heat, nutrients, pests, and diseases. A lack of water and excess heat are the most likely causes.
So, while mulberry trees get brown 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. Seasonal
Since mulberry trees are deciduous, it’s perfectly normal for their leaves to yellow, brown, and drop in the fall and winter.
The reason?
Deciduous plants go dormant in the colder months is to survive the weather (similar to bears hibernating). By shedding their leaves and pausing their growth, they’re able to conserve energy until the spring.
On the other hand, evergreen trees are typically those in tropical climates (with little to no frost), or have other methods of surviving winter.
For example, in the book The Hidden Life of Trees, professional forester Peter Wohlleben shares that pine trees have a type of antifreeze in their needles which allow them to survive the cold.
So, if your mulberry tree has yellow or brown leaves in the fall and winter, don’t worry as it’s normal behavior. The new leaves should regrow in the spring.
But if your mulberry tree has brown leaves in the spring and summer months, it’s likely an issue that needs to be addressed.
2. Under-Watering
The most common preventable reason why mulberry trees get brown leaves is a lack of water. When mulberry trees don’t have enough water, their leaves begin to dry out. If not addressed, their leaves will continue drying out, leading to curling, browning, and dropping leaves.
Under-watered mulberry trees can also have other issues such as flower and fruit drop.
The best way to water mulberry 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, under the tree’s canopy. Ideally, the soil moisture should be similar to a wrung-out sponge.
If you check your mulberry tree’s soil, and it’s bone dry, chances are this is why it has brown leaves.
Aside from following the above recommendation, make sure to soak the tree’s soil down to about 2 feet. This is because 90% of the tree’s roots are found at this depth. Doing this also encourages the tree to grow deeper roots to access deeper water, making it more independent and requiring less water.
However, there are times when watering isn’t enough on its own.
Apply 2 inches of compost and 4-12 inches of mulch under the mulberry tree’s canopy.
Compost not only provides valuable nutrients but improves the soil’s richness. Every 1% increase in the soil’s richness or organic matter leads to an additional 20,000 gallons of water held per acre (source).
On the other hand, mulch reduces evaporation, regulates soil temperature, and prevents soil erosion. Mulch also breaks down into nutrients over time.
The goal is to mimic a mulberry’s natural environment—an understory tree in a forest. This means providing partial shade (especially from the afternoon sun), and plenty of mulch.
In forests, mulberries would be naturally mulched from the tons of leaves and branches from other plants, so aim to do the same!
3. Extreme Heat
Even with applying proper water, compost, and mulch, extreme heat can dry out the mulberry tree’s leaves faster than the tree can cool them. When this happens, the leaves dry, curl, brown, and drop.
Mulberry trees do best in USDA hardiness zones 4-8 (source). This generally means temperatures between -20ºF and 85ºF. If temperatures rise above 90ºF, mulberry tree leaves will likely begin browning.
Before caring for mulberry trees in hot weather, it may help to know how these plants keep themselves cool in the first place.
The two main ways plants cool themselves are by sending moisture from their roots to their leaves, and by a process called transpiration.
Much like how humans exhale and release moisture in our breath, plants do the same. This is called transpiration and it’s the reason why walking into a forest or a thick canopy can feel extremely humid.
So while the top side of a plant’s leaves is like a solar panel (photosynthesizing), the underside is for breathing and cooling.
Fun Fact: Opposite of humans, plants inhale carbon dioxide and exhale oxygen. It’s pretty cool how humans and plants balance each other in this way.
Let’s take a look at some ways you can keep mulberry trees cooler in hot weather.
Hot Weather Tips
- Compost and mulch – as mentioned earlier, compost and mulch are incredibly effective practices for keeping mulberry trees properly watered and cool.
- 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 leaves increase the 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
| 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 |
When mulberry trees get too little or too many nutrients, the tree becomes stressed and leads to leaves yellowing, browning, or dropping (or all of the above).
The two main ways to fertilize mulberry trees are by using chemical fertilizers or compost.
While chemical fertilizers are effective in the short term, many gardeners are finding long-term consequences such as fewer pest predators, pollinators, and dry (dead) soil. This generally leads to dealing with more pests and diseases, and increasing irrigation dramatically.
So, it’s not a surprise that many of these gardeners are replacing chemical fertilizers with compost.
If you do decide to use a chemical fertilizer, aim for a balanced NPK (nitrogen, phosphorus, and potassium). For example, a 10-10-10 works nicely.
Generally, young mulberry trees need more nitrogen as they’re focused on foliage growth (nitrogen being the main nutrient of leaves), while mature mulberry trees need phosphorus and potassium for proper flower and fruit development.
Other secondary nutrients such as iron and magnesium are included in most fertilizers in sufficient amounts.
If you’d like to see my recommendations for both compost and fertilizer, check out my recommend fertilizer page.
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 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.
