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5 Reasons Mulberry Trees Drop Fruit (& How To Fix It)

We’re looking at getting a mulberry tree, but a common problem I’ve heard is they often drop fruit. I couldn’t find much information on this, so I did some more digging. Here’s what I found.

Mulberry trees drop unripe fruit due to overbearing, improper watering, extreme weather, a lack of pollination, and certain pests and diseases. For best results, grow in USDA zones 5-10, only water when the top 2-4 inches of soil is dry, and apply compost and mulch. Ripe fruit that drops can be caught with a net.

So, while mulberry trees drop their fruit early for several reasons, how can we tell which issue is causing it, and how can we fix it? Let’s take a closer look.

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unripe berries on a mulberry tree

1. Overbearing

It’s normal for mulberry trees to drop any excess unripe fruit if the tree is overbearing. Overbearing occurs when the tree senses it doesn’t have enough nutrients, water, or weight-bearing branches to support the fruit.

As with most fruiting trees, it’s common for mulberry trees to lose the majority of their initial flowers and small buds.

The good news is there should still be plenty of fruit for you to enjoy.

Occasionally, mulberries and other fruiting trees have alternate or biennial bearing—fruiting heavily one year and fewer the next year. Because of an unusually heavy fruit load, the tree may need the entire next season to store sufficient nutrients and water again.

You can prevent alternate bearing by properly watering and fertilizing your mulberry tree. To see which fertilizers I use and recommend, check out my recommended fertilizer page.

Keep in mind that it’s normal for younger mulberry trees to drop larger amounts of unripe fruit as they’re focusing on establishing a proper root system and canopy. Once the tree develops a sufficient root system and canopy, its fruiting capacity should be greatly increased.

You can speed up this process by pruning excess and overlapping branches.

Mulberry Trees Dropping Ripe Fruit

If your mulberry is dropping ripe fruit, you probably have a good problem! It likely means that your mulberry has so much ripe fruit that it doesn’t know what to do with it. Here’s what you can do if your mulberry is dropping lots of ripe fruit.

  • Place a fine net under the tree to catch fallen berries
  • Make jams or preserves
  • Feed it to livestock

Now, let’s get back to the reasons why mulberry trees drop unripe fruit.

2. Improper Watering

Mulberry trees that are under or over-watered become stressed and shed their flowers and fruit before losing their leaves.

The tree’s leaves may also turn yellow or brown before dropping.

So, what’s the ideal way to water mulberry trees?

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. Ideally, the soil moisture should be similar to a wrung-out sponge.

When watering, make sure to soak the soil down to 2 feet, as over 90% of the mulberry’s roots are found at this depth.

By watering this way, you’re preventing both under and over-watering.

For even better results, apply 2 inches of compost and 4-12 inches of mulch.

Compost provides valuable nutrients and increases the soil’s richness. With every 1% increase in the soil’s richness or organic matter, an additional 20,000 gallons of water is held per acre (source).

Mulch simulates the fallen leaves and branches in a forest (which is how mulberry trees evolved) and reduces evaporation, regulates soil temperature, prevents soil erosion, and provides nutrients.

Reapply compost every 1-2 months and mulch every 3-6 months. Keep these materials at least 3 inches from your mulberry tree’s trunk.

However, if your soil has poor drainage, hold off on providing mulch as it can make the issue worse.

Poor Drainage

Here are my quick tips for amending poorly draining soils:

  • Planted mulberry trees: provide 2 inches of compost every 1-2 months
  • Potted mulberry trees: repot with fresh potting soil

Funny enough, compost fixes both poor and fast-draining soils as the organic matter not only breaks up the larger clumps of soil but is great at retaining the proper amount of moisture. Over time, your soil should be nicely amended.

3. Extreme Weather

USDA hardiness zone map
Source: USDA

When mulberry trees are too hot or cold they’ll begin to lose their flowers, buds, and fruit. Hot weather symptoms are leaves curling, drying, browning, and dropping. Cold weather symptoms are leaves browning and dropping. Sometimes, a quick cold spell causes leaves to drop before they can turn brown.

Mulberry trees do best when they’re grown in USDA hardiness zones 4-10.

However, the exact zone depends on the variety of mulberry you’re growing.

Mulberry TypeHardiness Zone
Red (Morus rubrum)5-10
Black (Morus nigra)7-10
White (Morus alba)4-8
Source

For more context, zone 4 means cold hardy down to -30ºF, while zone 10 is cold hardy down to 30ºF (little to no frost).

If you believe your mulberry tree is dropping its berries due to a hot or cold climate, here are some tips.

Tips for Hot Weather

  • Apply 2 inches of compost and 4-12 inches of mulch. These materials greatly improve the water retention of the soil and regulate its temperature. Since mulberries are primarily cooled by transporting moisture from their roots to their leaves, these two practices are highly recommended.
  • Provide partial shade, especially from the hot, afternoon sun. Mulberry trees evolved as a midstory species in forests, so they’re used to taller canopies giving them some shade. Ideally, use shade sails or other trees such as pines or oaks.

Tips for Cold Weather

  • Cover the tree’s canopy with a sheet to insulate it from wind chill. Tarps are also great at blocking wind chill and ice buildup.
  • Provide 1-2 feet of mulch. The more mulch, the more insulation the roots and the base of the tree will have.
  • Plant the tree in a south-oriented direction for maximum sunlight and warmth (if you’re in the southern hemisphere, this is north). Additionally, plant along a south-facing wall to reflect even more sunlight and heat onto the plant. This also keeps the tree a bit warmer into the night.

4. Lack of Pollination

mulberry flowers

Mulberry trees that don’t have sufficient pollination often drop their unfertilized flowers and fruits. Generally, flowers need to be pollinated (fertilized) to turn into fruit. While self-pollinating mulberry trees can fruit, they do best if they’re cross-pollinated.

Do You Need 2 Mulberry Trees to Get Fruit?

Mulberry trees are self-fertile and require no pollinator, however a pollination partner will increase the size and quality of the harvest. 

Raintree Nursery

So, while you can grow 1 mulberry tree by itself, it often does better with another tree planted near it. Generally, this is within 50 feet as it allows the pollinators to successfully reach both trees.

If you have multiple mulberry trees, ensure you’re pollinating trees of the same variety to maintain the same variety of fruit (unless you’d like hybrid fruits).

Tips to Improve Mulberry Tree Pollination

  • Keep another mulberry tree nearby. Ideally, within 25 feet, and no more than 50 feet. Any more than 50 feet and pollinators have a reduced likelihood of visiting both mulberry trees.
  • Plant companion plants (especially those that flower) within 50 feet of your mulberry tree. They’ll attract more pollinators including butterflies, bees, and hummingbirds.
  • Manually brush your mulberry tree’s flowers to spread pollen and induce fertilization. Use a clean q-tip, paintbrush, or toothbrush. This is especially helpful for indoor and potted mulberry trees as they’ll likely have limited access to pollinators.
  • Start beekeeping.

5. Pests and Diseases

Spider Mites and Thrips

a spider mite and thrip
A spider mite (left) and a thrip.

You can tell if your mulberry has spider mites if you see small dots running around on the tree’s leaves. Spider mite colors range from red, brown, yellow, and green. Common symptoms of spider mites on mulberries are leaves yellowing and dropping. Fruit dropping is also common as the mites weaken the tree (source).

On the other hand, thrips are winged insects that feed on the sap of the plant’s leaves. You can usually see small black dots (their waste) on the leaves. While thrips can’t kill a mulberry tree, they can stunt it and make it drop its fruit and leaves (source).

Mites and thrips also transmit a few mulberry viruses (likely Tospovirus) which cause unripe fruits to drop.

  • Mulberry Mosaic 
  • Mulberry Vein Banding Associated
  • Mulberry Ringspot

Prevention and Treatment

The best way to avoid the above conditions is to properly manage mite and thrip populations.

Like aphids, mites can be sprayed with water or neem oil (this worked to remove aphids from my Kaffir lime tree).

To prevent both mites and thrips, encourage their natural predators:

  • Green lacewing
  • Beneficial wasps
  • Ladybugs

To attract these beneficial insects (and make your job easier), avoid dust, pesticides, and plant diverse companion plants. If your mulberry’s leaves get dusty, give their leaves a quick rinse.

Popcorn Disease

popcorn disease on a mulberry tree
Image source: AgBiome

Popcorn disease (Ciboria carunculoides) is a fungus that causes mulberry fruits to swell and remain unripe and green, appearing similar to popcorn kernels. While this disease is only found in southern states in the US, it’s still a problem, especially for commercial growers.

Luckily, the disease is only limited to the fruits (not infecting the tree itself), so proper management and treatment such as sprays (more on sprays below) should limit it to certain fruits or eliminate it. Some seasons are also better than others.

Root Rot

Root rot, also called Phytophthora Root & Crown Rot, is a root fungus that causes 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!

A Note on Pesticides and Fungicides

My parents recently had an issue with caterpillars eating their basil plants, and they were about fed up. 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.

my moms basil plant and a tent worm caterpillar
Captain Jacks deadbug spray

If you’d like to find out more about this organic spray, you can find it on Amazon.

So, what’s my point here?

Even though chemical sprays and fertilizers may be an easy way out, like all easy and convenient things, there are usually long-term costs. Before using conventional 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 most 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 berry plants, fruit trees, and nut trees THRIVE.

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