by Devin Reese
Mulberry Season
It’s that time of year when mulberries are fruiting all around Northern Virginia. Sidewalks are dotted with squashed, blackberry-like fruits; and local animals are having a feast. Mulberries are eaten by a bevy of native birds—blue jays, mockingbirds, goldfinches, and robins, among others. Mammals such as squirrels, foxes, opossums, and raccoons adore mulberry fruits, too. And people also enjoy ripe mulberries.
Invasive Mulberries
While mulberries are attractive to and nutritious for wildlife and people, there’s a catch. Nearly all the mulberry trees we see in the NOVA region are an imported species—the white mulberry (Morus alba)—also known as the silkworm mulberry. M. alba is native to China, where it has been cultivated for nearly 5,000 years as a silkworm host tree. Silkworms feed on its leaves and yield the silk used to make clothing. As an interest in silk spread, so did the white mulberry tree—to the ancient Greeks and Romans, and eventually to the New World.
Unlike the red mulberry (Morus rubra), which is native to North American forests and river valleys, the imported white mulberry thrives in lower quality sites with poor soils. It has therefore become invasive in North America, cropping up in edges, yards, and urban parks where it outcompetes native species. White mulberry trees are so prolific and hardy that they’ve been outlawed in several U.S. states, including Illinois, Kentucky, and Tennessee. For more details, see: https://8billiontrees.com/trees/why-are-mulberry-trees-illegal/.
Species of mulberry, Morus
White mulberry – Morus alba
Black mulberry – Morus nigra
Red mulberry – Morus rubra ★
★ native to northern Virginia
Aside from being squeezed out, the original red mulberry trees are known to be negatively impacted by white mulberries in two ways:
1) Native red mulberries hybridize with the invasive white mulberry, muting the characteristics and compromising the genetic integrity of red mulberries.
2) White mulberries are suspected of transmitting a root disease to the native red mulberry trees, a disease that can be fatal to seedlings.
As its forest habitats continue to degrade, and competition with white mulberries intensifies, the red mulberry has become increasingly rare, and is now listed as a threatened plant species in some states.
You may also find a third species—the black mulberry (Morus nigra) in NOVA, or the lookalike but less closely related sandpaper mulberry (Broussonetia papyrifera) but these are not as invasive or pervasive as the white mulberry. Adding to the mulberry melee are many cultivars from nurseries.
What To Do About Mulberries?
Invasive white mulberry trees can be difficult to remove. In mature trees, the root systems are extensive, spreading both downward and horizontally. So, other than seedling-stage mulberries, they can’t easily be pulled out of the ground. A large white mulberry is typically removed by cutting it down to the stump, then drilling and filling holes with a target herbicide.
Given the challenge of removing mulberries, coupled with the complexity of the native-nonnative roles in ecosystems, it’s not always obvious whether to take out a white mulberry tree. A “decision tree” diagram from the Great Lakes Collaborative but also relevant to NOVA, can be used as a guide to for this decision. The female plants produce fruits, but males do not, as noted in the diagram below.
Most of us in NOVA live within five miles of a “lowland forest habitat,” suggesting that we should remove fruiting white mulberries when possible. But, since they support such an array of wildlife, removal should be accompanied by replanting of other species that provide food to birds and mammals.
The best choice would be a red mulberry tree (M. rubra). However, the hybridization with white mulberries has made it quite difficult to find a source for the native species. Says Matt Bright, Executive Director of Earth Sangha, “I’ve only seen a small handful of one that we think are genuinely M. rubra rather than M. alba. We haven’t grown them in ages. Our concern was both that it was getting harder to find seed, and that the seed we were germinating definitely gave the impression of being hybridized, with some traits on some seedlings consistent with white mulberry.” So, if you do choose to install a red mulberry, be sure it’s the real deal and not a hybrid.
Recommended alternatives that are native to NOVA and also have edible fruits include:
- cockspur hawthorn (Crataegus crus-galli)
- wild plum (Prunus americana)
- black cherry (Prunus serotina)
- eastern redbud (Cercis canadensis)
- tulip poplar (Liriodendron tulipifera)
- common pawpaw (Asimina triloba)
- black gum (Nyssa sylvatica)
- sassafras (Sassafras albidum)
Here are some more NOVA mulberry enthusiasts:
