Mulberry trees (Morus species) are popular for their fast-growing shade canopy and sweet, edible fruits. When considering planting one, a common question is whether a specific tree will produce fruit. The answer is straightforward: a male mulberry tree will not produce fruit. A tree’s potential to yield a harvest is entirely determined by its reproductive biology.
The Biological Reason for Separate Sexes
Many mulberry varieties are dioecious, meaning the male and female reproductive organs are housed on entirely separate individual trees. The male tree produces flowers containing only stamens, which are the pollen-producing structures. These male flowers lack the anatomical parts necessary to form a fruit.
Fruit development is solely dependent on the female tree. Female trees produce flowers that contain a pistil, which includes the ovary. The ovary must be successfully fertilized by pollen from a male tree to develop into the mature fruit.
After successful pollination, the female tree’s ovary swells and matures, forming the fleshy aggregate fruit that resembles a blackberry. Without the female flower structure, fruit cannot physically develop on a male tree.
The Male Tree’s Role: Pollen Production
The function of the male mulberry tree is to produce and release abundant quantities of pollen. The male flowers appear as small, elongated, hanging catkins designed to release pollen into the wind for dispersal. This wind-driven strategy makes male trees heavy pollen producers.
The high pollen count produced by male mulberry trees frequently associates them with seasonal allergies, triggering symptoms like allergic rhinitis. Many cities have historically restricted the planting of male mulberry trees to reduce airborne allergens.
Male mulberry trees are sometimes deliberately planted in landscaping as “fruitless” varieties. They are favored for shade because they do not drop messy, staining fruit, eliminating cleanup and bird attraction problems associated with female trees. These male trees lack the ovary structure and will never transition to a fruit.
Ensuring Fruit Production: Choosing the Right Cultivar
For a gardener seeking a harvest, the primary step is to ensure a female tree is planted. In strictly dioecious varieties, a separate male tree must be planted nearby to provide the necessary pollen for fertilization. Without a compatible male pollinator, the female tree will not set fruit.
Many gardeners choose to plant monoecious or self-fertile cultivars, which eliminate the need for a separate male tree. These varieties possess both male and female flowers on the same plant, allowing for self-pollination and guaranteed fruit production. The ‘Illinois Everbearing’ cultivar is a popular example known for its long harvest season and reliability.
If a tree is already established, one way to determine its sex before fruit sets is by inspecting the flowers in early spring. Male flowers appear as small, long, hanging catkins that are often yellowish-green. Female flowers, in contrast, are generally smaller and appear as rounder, less conspicuous clusters.