A reader reached out a few days ago and asked me why their mulberry tree isn’t fruiting. I had an idea, but I wanted to provide them with the best answer I could. So, I did some digging. Here’s what I found.
Mulberry trees won’t fruit if they’re too young or have improper pollination, watering, sunlight, or nutrients. Pests and diseases can also stress a mulberry tree, preventing it from flowering and fruiting. Ideally, only water when the soil is dry, provide compost and mulch, and provide 6+ hours of daily sunlight.
While any of the above issues prevent mulberry trees from fruiting, how can we identify which issue is causing it, and from there—how can we fix it? Let’s take a closer look.
1. Not Yet Mature
Grafting vs Grown From Seed
Grafted mulberry trees will fruit within the first 2-3 years. This is especially true of the ever-bearing mulberry variety. Occasionally, an ever-bearing mulberry fruits within its first year.
On the other hand, mulberry trees that are grown from seed can take between 5-10 years to start flowering and fruiting.
Mulberry trees normally fruit from June to September.
The reason behind this is that grafted trees use budwood from an already mature tree, so they’re essentially a clone and don’t need to wait to mature. Trees grown from seed are a child of the original tree (with brand new DNA) and need to properly mature before flowering and fruiting.
So, if your mulberry tree isn’t of age, then it likely explains why it doesn’t have normal fruit sets yet. Once it matures and establishes a canopy and root system, it should start fruiting regularly.
To find out if your mulberry tree is grafted or grown from seed, contact your seller or inspect the tree to see if you can find a grafting scar.
If don’t have a mulberry tree yet, I suggest the everbearing mulberry variety. You can find it at the Fast Growing Trees nursery (but make sure you can legally grow it in your area first)!
But what if your mulberry tree is mature and it’s still not producing fruit?
2. Lack of Pollination
While mulberry trees are self-pollinating, they do best if they are cross-pollinated with another tree of the same variety.
Mulberry trees are self-fertile and require no pollinator, however a pollination partner will increase the size and quality of the harvest.
RainTree Nursery
This is also true for other fruiting trees. Because of this, plant multiple mulberry trees of the same variety within 50 feet of each other. This is the appropriate distance between trees so pollinators have the best chance to visit both trees.
Some other ways to boost pollination are:
- Companion Plants
- Beekeeping
- Manual Pollination
If you’d like to manually pollinate your mulberry tree’s flowers, use a clean paintbrush, toothbrush, or q-tip, and lightly brush from flower to flower.
While you can plant mulberries of different varieties, you’ll likely get hybrid fruits (which some people prefer).
Now, if you have plenty of flowers and pollinators flying around, and your mulberry tree still isn’t fruiting, the next potential issue to look at is watering.
3. Improper Watering
When a mulberry tree has too little or too much water, the tree’s leaves, flowers, and fruits begin to dry and drop. If the tree is too stressed from improper watering, it might not have enough energy to begin flowering or fruiting.
A good way to tell if your tree is under-watered is if its leaves are curling, drying, browning, or dropping. Alternatively, symptoms of over-watering are yellow and dropping leaves. Sometimes the leaves are green when they drop.
The best way to water mulberry trees is to only water when the first 2-4 inches of soil is dry. You can check this by pushing a finger into the soil, under the tree’s canopy. The goal is to have soil moisture similar to a wrung-out sponge.
Make sure you’re soaking the soil at least 2 feet deep as 90% of the tree’s roots are found at this depth.
Additionally, apply 2 inches of compost and 4 inches of mulch.
Compost provides valuable nutrients and improves the soil’s water retention. Every 1% increase in the soil’s richness (organic matter) leads to an additional 20,000 gallons of water held per acre (source).
Mulch drastically reduces evaporation, regulates soil temperate, and prevents soil erosion. Since mulberries evolved as a temperate understory trees, they prefer partial shade and plenty of mulch in the form of leaves and branches.
As the permaculture guru Geoff Lawton says, “A forest grows from a fallen forest.”
Aim to reapply compost every 1-2 months and mulch every 3-6 months. Keep these materials at least 3 inches from the trunk as they can introduce mold.
By only watering when the soil is dry, and providing compost and mulch, you’re dramatically reducing the likelihood your mulberry tree will be under or over-watered. And as a result, you’re giving it the best chance of fruiting.
4. Lack of Sunlight
It’s no secret that plants need photosynthesis to produce energy, and much of this energy is needed for the tree to produce fruit. If mulberry trees get less than 4 hours of daily sunlight, they’ll likely have issues flowering and fruiting.
Because of this, provide your mulberry trees with at least 6 hours of daily sunlight.
Keep in mind that mulberry trees do best in USDA hardiness zones 4-8, so they prefer temperatures between -20ºF and 90ºF.
If mulberry trees get too hot or cold, they’ll become stressed and show signs such as leaves, flowers, and fruit discoloring or dropping. When mulberry trees are too weak, they’ll be unable to produce new leaves, flowers, and fruit.
Since mulberry trees are deciduous, they go through dormancy in the winter and need chill hours (under 45ºF) for proper fruiting.
If the mulberry tree experiences a warmer winter, it might think it’s springtime and break dormancy and grow leaves and flowers. This can pose a problem as a later frost can easily kill the young leaves and buds. If the frost is bad enough, the entire mulberry tree can die.
The best way to provide mulberry trees with appropriate sunlight is to plant on the south side of your property (if you’re in the southern hemisphere, this is on the north side). The south offers the longest sun exposure, so planting in this orientation almost guarantees your mulberry gets enough sunlight.
5. 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 a decline in health and fruiting.
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, soak your mulberry tree’s soil to dilute the existing fertilizer and allow it to flow 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 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 several months, there’s a good chance a lack of nutrients is causing little to no fruiting.
However, symptoms of a lack of nutrients 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 prevent a lack of nutrients for your mulberry tree.
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, use 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 goes a lot further and adds to the water retention and nutrients.
Generally, I prefer using compost over fertilizers, and many gardeners are finding that compost is replacing 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.
Keep in mind that 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 and the tree is more likely to develop other issues.
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.
6. Pests and Diseases
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!
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).
Leaf Scorch
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 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.
