While a plant's sex may not be as easy to spot as most animals, many trees are of one gender or the other. In some cases, gender lines break down among individual flowers; in other cases, a single flower is "perfect" and has both male and female sex organs. However sex manifests for a given species, it's especially important to take your trees' sexes into account when looking to grow fruit trees. Plant a grove that's 100 per cent female trees and you'll get a 0 per cent yield.
Dioecious Versus Monoecious
Flower structure is the most basic expression of sex in a plant, potentially male, female or both, which is called a perfect flower. Dioecious plants are those species that have male and female flowers on separate plants. By contrast, monoecious species may have male and female flowers growing off a single plant. For reproduction to occur, one dioecious plant must be growing close to another plant of the opposite sex. On the other hand, monoecious plants are not necessarily self-pollinating; in some cases, they also rely on a second plant for pollination and reproduction to occur. For example, the pawpaw tree is monoecious but is not self-pollinating.
It's easiest to identify a tree's sex when it puts out blooms. If the tree's flowers have well-developed ovaries and stigmas, usually shaped like long, central stalks, then they are female. If a tree's flowers lack these stigmas and have multiple stamens, instead, they are male. Because flower structures can vary tremendously among species, it's best to refer to a photograph of a female or male flower of the species in question. You can also determine that you have a female tree if it begins to fruit. On the other hand, the absence of fruit is not a sure-fire sign of a male tree; you may also have a female tree that isn't experiencing the right conditions to fruit.
Several species of fruit trees break down along gender lines, making it necessary to plant both male and female trees within a small area in order to ensure fruit production. For example, the kiwi fruit is dioecious and thrives in a ratio of one male plant for every six to 10 female plants. Persimmon trees are also typically dioecious, though they may switch sex from one year to the next and, occasionally, a male tree produces a perfect flower.
In some cases, a tree is not strictly monoecious or dioecious. For example, the papaya may grow as a male, female or bisexual plant, with both types of flowers. Avocado trees are technically monoecious, having perfect flowers with both male and female organs. However, a tree may have flowers of "type A" or "type B." Type A flowers open in the morning as receptive females and then close in the afternoon. The following day, they open in the afternoon and shed pollen, serving as males. Meanwhile, type B flowers follow the opposite schedule. In some cases, it's necessary to plant trees with both type A and type B flowers to ensure fruit production.