I’m doing a permaculture design for a client, and their mulberry trees are recently getting some yellow leaves. To help them out, I did some research. Here’s what I found.
It’s normal for mulberry tree leaves to get yellow and drop in the fall and winter as the tree becomes dormant. However, if its leaves are yellowing in the spring or summer, it’s likely due to over-watering, improper nutrients, a lack of sunlight, or diseases such as leaf scorch.
So, while mulberry trees get yellow leaves from several causes, how can we tell which one it is, and how can we fix it? Let’s take a closer look.
Mulberry trees are deciduous, so their leaves naturally yellow, brown, and drop in the fall and winter. This is a survival strategy many plants picked up to successfully live in cooler, more temperate climates. By shedding their leaves, the plants enter a dormant state—similar to a bear hibernating.
Typically, deciduous plants require chill hours to stay in dormancy (under 45ºF). Mulberry trees require about 400 chill hours for proper dormancy, leading to better flowering and fruiting in the spring (source).
On the other hand, evergreen plants (such as citrus trees) keep their leaves year-round. These plants either developed other ways to survive the cold, or live in tropical climates (with little to no frost).
So, if your mulberry has yellow or brown leaves in the fall or winter, know that this is normal. However, leaves with yellow or brown spots are different and can indicate disease (more on this later).
If this is the case for your mulberry tree—you shouldn’t need to fix anything. If temperatures drop below -30ºF (zone 4), insulate the tree with mulch, sheets, or a windbreak. Other than that, simply wait for spring!
However, what happens if your mulberry tree has yellow leaves in the spring or summer?
The most common reason why mulberry tree leaves yellow and drop is stress from over-watering. This is especially common in soils with poor drainage.
Over time, waterlogged soil can develop mold and lead to root rot (also called Phytophthora root and crown root). Root rot slowly decays the mulberry tree’s roots, causing drooping, curling, and yellowing leaves. Over several days to a few weeks, it can kill the plant.
So, what’s the optimal way to water mulberry trees?
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. Additionally, provide 2 inches of compost and 4 inches of mulch such as leaves, bark, straw, or pine needles.
By only watering when the soil is dry, you’re preventing both under-watering and over-watering. This helps the plant establish water independence—eventually requiring little to no supplemental water (depending on your climate).
Additionally, water until the soil is saturated down to 2 feet deep. By watering to this depth, you’re providing water to over 90% of the mulberry tree’s roots.
Mulberry trees that are watered with frequent and light watering typically only grow extremely shallow roots. After all, why would they grow deeper roots if the water and nutrients are only on the surface?
This keeps the plant at a disadvantage as their shallow roots mean they’re poorly prepared for windy weather and droughts (unable to access the deeper water).
So, if you want your mulberry tree to be more self-sufficient and have a better chance of surviving the occasional drought, water it only when the soil is dry and down to 2 feet deep.
However, soils that have poor drainage (common with clay soils) can complicate this process.
Generally, mature mulberry trees are hard to amend as there are large volumes of soil (needing large amounts of amendments). Because of this, the best way to amend the soil for better drainage is to apply 2 inches of compost on top of the soil every 1-2 months.
Over time, the smaller particles will work their way into the deeper soil. Avoid excessive mulching at this time it can further lock in the moisture.
On the other hand, potted mulberry trees with poor drainage can be amended fairly quickly by repotting them with fresh potting soil. Since the roots are limited to the pot, they generally don’t get as much transplant shock as digging up planted mulberries with spread-out and established roots.
But, what if we’re watering our mulberry correctly? What do we check next?
3. Improper Nutrients
Excess nutrients are typically caused by over-fertilizing mulberry trees. This can lead to the potential burning of the tree’s roots, causing the plant stress and developing drooping, curling, and yellow leaves. Other symptoms such as flower and fruit dropping can also result.
Over-fertilization is generally caused by fast-release fertilizers, as compost isn’t potent enough.
However, a lack of nutrients also causes yellow leaves.
Lack of Nutrients
|Entire leaf is pale or yellow
|Dark green veins, rest of the leaf is yellowing
|Broadly pale leaves, foliage color looks mottled or smeared
A lack of nutrients also causes stress to the mulberry, which then develops yellow leaves. Insufficient nutrients are commonly caused by poor soils, leaching, and other stressors.
Nutrient leaching is when soils have too much drainage or are over-watered and the nutrients seep too far down into the soil, out of reach of the plant’s roots.
The Best Way to Fertilize Mulberry Trees
You can choose to fertilize your mulberry tree’s soil with fertilizer or compost. If you choose store-bought fertilizer, aim for a balanced NPK (nitrogen, phosphorus, and potassium).
Generally, while chemical fertilizers have nutrients in quantity, they typically don’t have nutrients in quality. So, chemical fertilizers might be sufficient over the short term, but over the long term, they often cause damage by short-circuiting the nutrient exchange between the plant and its beneficial soil life.
This leads to dry and dead soil (dirt) and overall decreased plant health.
On the other hand, compost provides more than sufficient nutrients, increases water retention, and promotes healthy soils. For example, every 1% increase in the soil’s richness (organic matter) leads to 20,000 more gallons of water absorbed per acre (source).
Many gardeners are even finding that compost is successfully replacing their fertilizers.
If you’d like to see my recommendations for both compost and fertilizer, check out my recommend fertilizer page.
Aside from nutrients, keep in mind that mulberry trees need a balanced soil pH between 5.5 to 6.5 (source).
The reason why mulberry trees prefer soil with a slightly acidic pH is that it’s ideal to dissolve nutrients in the soil.
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 mulberry tree’s soil is too alkaline (above 6.5) you can add acidic amendments such as coffee grounds, sand, and peat moss. On the other hand, if its soil is too acidic (below 5.5), add alkaline materials such as wood ash, charcoal, or lime.
Additionally, cold and/or wet soils are not good at promoting nutrient uptake as the mulberry tree will either be slightly dormant during the cold or too stressed in wet soils.
If you’re growing your mulberry tree in a container, aim to have at least a 15-gallon pot as the mulberry tree’s roots need a bit of room to spread. However, it’s not typically recommended to grow mulberry trees in containers as they outgrow them quickly.
4. Lack of Sunlight
Mulberry trees generally require at least 6 hours of sunlight to photosynthesize properly. Without it, their leaves turn yellow and they’re unable to develop sugars for the plant. Over time, this low energy leads to the plant’s declining health, and eventually, the tree can die.
Tips to Increase Sunlight
- Plant the mulberry tree in a south-facing direction for maximum sunlight (north-facing if you live in the southern hemisphere)
- Plant the tree along a south-facing wall to reflect more sunlight and heat onto the tree (some heat even persists into the night).
- Prune some overstory trees that are blocking the mulberry’s canopy from the sun. You can also prune the mulberry tree itself to allow more light to reach the mid and lower branches. This new space also increases aeration from the sun and wind—discouraging disease from spreading.
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, 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 is a bacterial disease (Xyllela fastidiosa) that causes mulberry leaves to yellow, brown, and drop. Occasionally, entire branches 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 (source).
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.