Tree life starts with a seed. The female and male parts come together to start a new life. Pollen flows from males in the spring to find the female’s egg and a new tree begins. The pollen finds the egg with the help of the wind or pollinators such as birds, bats, butterflies, or bees.

Strict gender concepts of male and female sexuality that are obvious with animals are blurred when applied to trees. Trees are on the spectrum. Male and female parts can be on the same tree - oak, birch, pine, or on separate trees - yew, willow, ginkgo for example. A tree may even start out as male and become female decades later. Some trees end up entirely female before they die, putting all their remaining stored resources into seeds. Other trees can change gender from one season to the next, over their life, or as the environment changes. For example, in one maple species, 10% of young sexually mature trees in a forest changed gender from year to year. A male ginkgo tree considered a National Monument in Japan, developed a single female branch.  

Fruits and flowers of female trees can be perceived as undesirable. The fluffy seeds of cottonwood seem to get everywhere, including into eyes. The ginkgo fruit smells like dog vomit, and flower petals can track in the house. Seeds and fruits require more energy for the tree to produce than pollen, therefore the reproductive costs of being female are usually higher than for the male. This may explain why some male trees tend to grow faster, reach a bigger final size and have a lower death rate than females.

Over the years male only selections of several common landscape trees have come to dominate our yards and gardens - the seedless coffeetree, seedless maple, seedless ginkgo, etc. The problem with this ‘sexist’ landscape is that while male trees are perceived as litter-free, they all produce abundant allergenic pollen, making a miserable spring for people with allergies and asthma.

The type of flowers or cones a tree produces determines tree gender. Tree flowers can have male parts, female parts, both male and female parts together, or none at all. You cannot tell flower function (or gender) just by looking. Trees do not show their gender identity until they are sexually mature and start to flower. Sexual maturity varies and can occur from 1 to 50 years of age. For example, the minimum tree age for seed production in shellbark hickory is about 40 years.

Trees being rooted in one place their whole lives, have developed creative ways of propagating their species. There is a sense that trees disregard binaries, and almost gleefully defy heteronormative modes of reproduction. It may be one of the ways trees have survived for hundreds of millions of years. Whatever they are doing, we have much to learn from them.

The fringed burl-like masses on the ash shoot are caused by the ash flower mite gall. The mite only feeds on the male flowers on the male ash tree. The mite does not harm the tree, only its appearance. 

Male cones of a spruce tree drop to the ground, finished with their task of releasing pollen. These are easy to see as the male cones are found on the tips of the lower branches. Spruce trees contain male and female parts on the same tree.

An easy identifier of a female buckthorn shrub is dark purple to black fruits in late summer and fall. Male buckthorn shrubs are fruitless.  

Birches have both male and female parts on the same tree. The male flowers called catkins, look like upright clusters found on the tips of shoots that will last through winter and mature in the spring.

The female seed pods of the Kentucky Coffeetree turn brown in late summer. If you would like a seedless tree, choose the male cultivar ‘Espresso’.