Mulberries

Mulberries of nursery rhyme fame are the fastest plants on Earth. 

​But before we delve into the particulars of this delicious tree fruit, I have to share what I learned while tracking down the nursery rhyme lyrics. 

Mulberries (Cwambier) CC BY-SA 4.0

According to historian R. S. Duncan, Here We Go ‘Round the Mulberry Bush comes to us from a British women’s prison in the 1840s. They had a mulberry tree in the prison exercise yard, and the inmates were required to exercise around it. Other nursery rhymes can be surprisingly sinister if you do a little research, but I’ll leave that to you. Let’s get back to the garden.

Mulberry description

Mulberries are cousins to figs. There are several regional variations on the mulberry tree, but we will be discussing members of the Morus genus. Mulberry trees are usually wider than they are tall. Some cultivars can reach 80 feet, though most are significantly shorter. You can keep yours trimmed to whatever height you prefer. The bark is smooth and pale orangish-brown while young, turning gray and furrowed as the tree matures. These trees grow quickly at first, but they are generally slow growers.

These are deciduous trees that produce fruits that look like long blackberries. There are three major cultivars: black, red, or white (Morus nigra, M. alba, and M. rubra, respectively). But most white mulberries are black. Let me explain.

The first black mulberries brought to England happened to be a white mutation, so everyone called them white mulberries. When cuttings were grown, the fruit was black. You can tell the difference between black and white mulberries by looking at the leaves. Heart-shaped, serrated black and red mulberry leaves are hairy underneath and bristly on top, while lobed white mulberry leaves are smooth. 

​White mulberries are native to South Asia and considered invasive in Brazil and the United States. Black mulberries are native to Iran, and red mulberries are native to eastern and central North America. Black and red mulberry trees have the most flavorful fruit, while silkworms prefer white mulberry trees. But you probably don’t want to grow white mulberries because of the pollen.​

Mulberry pollen

White mulberries are often banned because they cross-pollinate readily with red mulberry. But there’s more than that to mulberry pollen. Mulberry flowers release their pollen at approximately 380 miles per hour, which is more than half the speed of sound. This makes them the fastest plants on Earth. This pollen is responsible for many bans, but not because of the speed. Instead, it is a matter of quantity. The sheer volume of pollen released by male mulberry trees is enough to be hazardous for people with asthma or other respiratory problems. Female mulberry trees absorb that pollen but check with your local government to see if they are allowed before you start planting.

Mulberry fruits

Mulberries are multiple fruits, like pineapples and figs, made up of drupes. They start green, yellow, or white. Most of them ripen to a deep purple or black. They do this because they contain anthocyanins. Anthocyanins are frequently touted as having antioxidant properties. They are what give plants their blue or purple color. While the antioxidant ability of anthocyanins does occur in test tubes, research has not yet been able to demonstrate that that ability carries over into real life. It ends up that we only retain about 5% of the metabolites responsible for antioxidant properties. That’s okay. Mulberry trees look nice, taste delicious, and they provide lots of vitamin C and iron.

Female catkins of black mulberry (JJ Harrison) CC BY-SA 3.0

Unopened male mulberry catkin (FASTILY TALK) CC BY-SA 3.0

Mulberry flowers

Mulberry trees have both male and female flowers, called catkins. Black mulberries are monoecious, with both sexes on the same tree. This makes them self-fertile. Red mulberries can be monoecious or dioecious. Dioecious trees are male or female and are not self-fertile. I’m not sure about white mulberries. Just be sure to read the label if you are buying mulberry cuttings if you want fruit.

How to grow mulberries

Unlike most other fruit and nut trees, which are best grown from bare root stock, mulberries can be grown successfully from root cuttings or stratified seeds. Seed- and cutting-grown mulberry trees tend to be healthier and sturdier. I don’t know why. I do know that seeds should be stratified for 2 or 3 months at 34°F to 40°F.

They do require some patience, however. Like avocado trees, mulberries can take 10 to 15 years to produce fruit. While some specimens are said to live 125 years or more, the longevity of mulberry trees has come into question as several specimens are most short-lived.

Mulberry trees prefer slightly acidic, light, loamy soil. These are lowland trees commonly found along river banks, forest edges, and on sheltered slopes. They can tolerate drought and dappled shade but perform best when conditions are warm, moist, and sunny. Black mulberries can tolerate poor soil, but red mulberries need healthier soil to thrive. Mulberry roots are very brittle and need to be handled with care.

Young mulberry fruit clusters (Ankur Jain) CC BY-SA 4.0

Mulberry tree care

In Britain, home growers often train grapevines up their mulberry trees. This is said to help prevent fungal diseases from occurring.

In commercial groves, mulberries are cut back to a height of 6 feet each fall (pollarding) and the removed branches are used to make baskets. In home gardens, mulberry trees should only be pruned when they are in full dormancy and only when completely necessary to remove dead or poorly placed branches. Mulberry trees bleed heavily when cut and some people are sensitive to the milky sap and unripe fruit of red mulberry trees, so you may want to wear gloves when working with them. (The trees, not the people). Unripe fruit may also give you a tummy ache, but young leaves can be cooked or eaten raw.

Mulberry problems

Mulberries are pest tolerant, but birds, raccoons, and squirrels will certainly want some of your harvest. Surface roots may also become problematic. Black mulberry trees are susceptible to Armillaria root rot (Armillaria mellea), also known as honey fungus, while red mulberries tend to be resistant. All mulberries are vulnerable to bacterial blight, crown gall, hairy root disease, and mulberry mosaic virus (MMV).

​Mulberry trees can be very messy. The fruit is easily bruised and starts to rot soon after ripening. This is probably why we don’t see them in grocery stores. You probably don’t want to plant one near a sidewalk or patio, as the fruit can stain.

​​Many mulberry growers install a soft ground cover under their mulberry trees to cushion the fall of ripe fruit. You could also hang tarp hammocks to catch the fruit.

Mulberry leaf with mulberry mosaic virus. (William M. Brown Jr., Bugwood.org) CC BY 3.0 US

​Mulberry trees are lovely and the fruit is delicious. Do you have room for a mulberry tree?