The question of whether a seed is male or female is common, but it stems from a misunderstanding of plant biology. Seeds themselves are not sexed; they are reproductive vessels. A seed is the biological result of fertilization, containing an embryo that carries the genetic blueprint for the future plant. The sex, or the reproductive organs of the plant that will eventually grow, is determined by the genetics encased within the seed. This genetic code dictates whether the mature plant will produce male, female, or sometimes both reproductive structures.
The Seed is an Embryo, Not a Sex
A seed’s primary function is to serve as a survival package for the plant embryo. It is composed of three main parts: the seed coat, which provides physical protection; the endosperm, a starchy tissue that acts as a food reserve; and the embryo itself. The embryo is the miniature, dormant plant, a product of the fusion of male and female gametes.
Thinking of a seed as having a sex is similar to asking if a fertilized animal egg is an adult male or female. The seed is merely the starting point in the life cycle, a self-contained unit of genetic potential. Its destiny—the expression of male, female, or combined sexual characteristics—lies in the interaction between its inherited DNA and its environment as it grows. The seed is a temporary, non-sexual stage.
Genetic and Environmental Sex Determination
The sex of a plant is primarily determined by its genetics. This can involve sex chromosomes, similar to the X and Y system found in animals, though this is less common in the plant kingdom. In many dioecious species, specific genes or gene complexes dictate the development of male-only or female-only flowers. This genetic determination is fixed at fertilization and establishes the plant’s inherent potential.
Plants exhibit a high degree of phenotypic plasticity, meaning environmental factors can significantly influence how genetic potential is expressed. Stressors such as extreme temperature fluctuations, nutrient deficiencies, or alterations in light cycles can trigger a shift in sex expression, especially in species that naturally separate the sexes. The application of certain plant hormones, like gibberellins, can also push a genetically female plant toward expressing male characteristics.
This ability to influence sex expression is the basis for creating “feminized seeds,” a technique used in crops like cannabis. This process involves chemically treating a genetically female plant, often with Silver Thiosulfate (STS), which suppresses ethylene production and forces the plant to develop male pollen sacs. Since the donor plant is female, the resulting pollen contains only female chromosomes (XX). When used to pollinate another female, the resulting seeds are almost guaranteed to produce female plants.
Monoecious and Dioecious Systems
Plant sex is best understood by looking at the two major reproductive strategies: monoecious and dioecious systems. Monoecious plants, such as corn, squash, and cucumber, bear both male and female reproductive organs on the same individual plant. The male flowers, which produce pollen, and the female flowers, which produce ovules, may appear at different locations or times on the single plant.
In contrast, dioecious species, which account for a small percentage of flowering plants, have separate male and female individuals. Examples include holly, kiwi, asparagus, and certain hemp varieties. For these plants to reproduce, a male plant must be present to supply pollen to a nearby female plant, making the sex of the individual plant a practical concern for growers.
Kiwi growers must ensure they have both male and female vines, as only the female plants produce the desired fruit, while the male plants are simply for pollination. Conversely, in crops like asparagus, male plants are often preferred for harvest because they do not expend energy producing seeds, resulting in larger, more vigorous spears.
Identifying the Plant’s Sex After Growth
It is impossible to determine the sex of a plant by looking at the seed; sex can only be identified once the plant has grown and entered the reproductive phase. This stage typically begins during the pre-flowering period, which occurs at the end of the vegetative cycle, often four to eight weeks after germination, depending on the species.
To identify the sex, a grower must examine the nodes, which are the junctures where the leaves and side branches meet the main stem. Female plants will first develop small, teardrop-shaped structures called calyxes, from which wispy white hairs, known as pistils, will emerge. These pistils are the receptive parts of the female flower.
Male plants develop small, smooth, round sacs at the nodes, which are their pollen sacs. These sacs appear like tiny balls and will not produce white hairs. For dioecious crops where only the female is desired, these male plants must be identified and removed promptly to prevent them from releasing pollen and causing the female plants to switch energy from producing flowers to producing seeds.