Research the plant in question. Although the steps listed below are fairly consistent, the more you know about the plant, the more accurate your result will be.
Wait for the plant to bloom. Flowers are the key to determining the sex of a plant. Once the plant has bloomed, examine the flower closely.
Look for the stamen. The stamen consists of the filament, a thin stalk within the petals and outside of the pistil, and the anther, nodes of pollen located at the top end of the filament. A well-developed stamen, or a high number of stamen, usually indicates a male plant.
Look for the pistil. The pistil, located at the center of the flower, consists of the style, a vase-shaped pod that contains the ovule and ovary of the plant and will eventually contain seeds, and the stigma, which is the opening of the "vase" located at the top of the style. A well-developed pistil, also known as the carpal, usually indicates a female plant.
Observe the plant. Certain trends can help you determine if the plant is male or female. Female plants produce seeds; seeds can take the form of seed pods, nuts or fruit. Male plants produce pollen; pollen can be seen in the air or dusting nearby objects. As a general rule, female plants will make more of a "mess" by dropping seeds, and male plants will produce more pollen.