Most flowering plants carry both sexes, often inside a single flower. In a minority of species, including holly, kiwi and cannabis, each plant is either male or female, and only the females ever bear fruit or seeds. Growing that fruit is costly enough to change how each sex grows, copes with drought and fends off insects.
Which Plants Have Separate Sexes
Plant sex comes down to flower parts. The male parts are the stamens, thin stalks tipped with pollen sacs. The female part is the pistil, whose swollen base holds the seeds-to-be and ripens into the fruit. A plant with only stamens can never make fruit itself, and a plant with only pistils needs pollen from somewhere else.
Most flowering plants, such as roses, tomatoes and apples, have both parts in the same flower. Some, like squash, corn and oaks, have separate male and female flowers on the same plant. About 15,000 to 15,600 species, roughly 5 to 6% of flowering plants, have male and female flowers on separate plants.1bioRxiv. Dioecy in plants: an evolutionary dead end? Insights from a population genomics study in the Silene genus2PubMed. The relative and absolute frequencies of angiosperm sexual systems: dioecy, monoecy, gynodioecy, and an updated online database Separate sexes show up in 43% of plant families and arose independently hundreds to thousands of times.3PubMed. The relative and absolute frequencies of angiosperm sexual systems: dioecy, monoecy, gynodioecy, and an updated online database
A gardener may already own some. Holly, kiwi, asparagus, ginkgo, sea buckthorn and cannabis all come as separate male and female plants, and so do many willows, poplars, ash trees and junipers. Asparagus growers often prefer male plants, which put their energy into spears rather than berries.
Not every plant fits neatly. Papaya can be male, female or hermaphrodite, with both parts in one flower. Some species mix hermaphrodite plants with female-only ones. A ‘self-fertile’ kiwi on a garden label is a variety bred to carry both functions.
In many separate-sex plants, sex is set by sex chromosomes, much like X and Y in people. Papaya uses an XY system with two kinds of Y, one making males and one making hermaphrodites. Plant hormones then steer each flower toward male or female parts.
How to Tell a Male Plant From a Female
Before flowering, male and female plants of most species look nearly identical. Guessing from leaf shape, size or vigor is mostly a coin toss. The dependable way is to look at the flowers once they open. Male flowers show stamens that shed yellow dust when tapped. Female flowers have a central pistil with a small green swelling at the base. A plant that has set fruit or berries is female or carries female flowers.
Because a plant may flower only once a year, for a short window, check it daily then and note which parts appear rather than judging from one glance. A tree can take many years to flower for the first time, so a holly or ginkgo bought as a seedling may be unsexable for a long while.
Male plants often put on a bigger show. In white campion, male plants carried more flowers, and those flowers gave off more scent than female ones.4PubMed Central. How to be an attractive male: floral dimorphism and attractiveness to pollinators in a dioecious plant5PubMed Central. How to be an attractive male: floral dimorphism and attractiveness to pollinators in a dioecious plant So a plant covered in many strongly scented blooms may be the male, though this varies by species and is only a hint; the flower parts are the real test. In some shrubs it is the female flowers that make more nectar and draw more flies and bumblebees.6PubMed. Small but attractive: female-biased nectar production and floral visitors in a dimorphic shrub
Here is what to look for on common plants:
- Holly: male flowers have four pollen-tipped stamens; female flowers have a green bead in the center.
- Kiwi: females have a large white starburst pistil; males have only a ring of dark stamens.
- Cannabis and hemp: females show white hairs from small pods; males hang little pollen sacs like grape clusters.
- Ginkgo: males drop catkin-like strings; females form paired small knobs that become smelly seeds.
If you need a specific sex, buy a plant of known sex. Named holly and kiwi varieties are usually sold labeled male or female because they are grown from cuttings. Seedlings are a gamble until they flower, so ask the nursery for a labeled cultivar.
Why Female Plants Pay a Higher Price
Pollen is cheap compared with fruit, so most of a plant’s reproductive spending goes to the female side once seeds develop.7PubMed. Patterns of biomass allocation to male and female functions in plants with different mating systems A female that fruits heavily has less left for leaves, roots and wood. In white campion, male leaves took in carbon slightly but consistently faster than female leaves, though the females used water more economically.8American Journal of Botany. Sexual differences in gas exchange and response to environmental stress in dioecious Silene latifolia (Caryophyllaceae)
The cost arrives once fruit starts swelling, not at flowering, so a female may look as vigorous as a male in spring and slow down as the fruit ripens. A heavy crop can also leave her with less energy to set flower buds for the next year, one reason some fruiting plants alternate between big and small crops. A male never carries fruit, so his growth is steadier through the season.
Shade, drought and poor soil hit the sexes differently. In low light, a female water plant cut back fruit more than males cut back flowers, while protecting its leaves.9PubMed Central. Light Availability and Patterns of Allocation to Reproductive and Vegetative Biomass in the Sexes of the Dioecious Macrophyte Vallisneria spinulosa Under mild drought, male poplars grew more and photosynthesized faster than females.10PubMed Central. Drought Stress Might Induce Sexual Spatial Segregation in Dioecious Populus euphratica—Insights from Long-Term Water Use Efficiency and Growth Rates Under severe drought, female poplars used water more efficiently and seemed likelier to survive.11PubMed Central. Drought Stress Might Induce Sexual Spatial Segregation in Dioecious Populus euphratica—Insights from Long-Term Water Use Efficiency and Growth Rates In another poplar, heat combined with drought harmed females more than males.12PubMed. Sex-specific responses of Populus cathayana to drought and elevated temperatures
Soil nutrients matter too. When phosphorus ran short, male poplars coped better, partly through stronger partnerships with root fungi, but with plenty of phosphorus, females grew larger and built bigger root systems.13Journal of Plant Ecology. Sex-specifically responsive strategies to phosphorus availability combined with different soil nitrogen forms in dioecious Populus cathayana14PubMed. Sex-specific strategies of phosphorus (P) acquisition in Populus cathayana as affected by soil P availability and distribution In natural stands, males tend to dominate drier, poorer ground and females richer, deeper soils.15PubMed Central. Testing predictions of spatial segregation of the sexes and life‐history theory in three species of the dioecious genus Baccharis L. from southeastern Brazil
In your yard, a female holly or kiwi on thin, dry soil may fruit poorly and grow slowly. Extra water and compost in fruiting season help females most. Females are not simply weaker; they trade growth for fruit, and some outlast males in extreme drought.
Which Sex Insects Prefer
Across many species, male plants carried more plant-eating insects and suffered more leaf damage than females.16Oikos. Sex‐biased herbivory: a meta‐analysis of the effects of gender on plant‐herbivore interactions Males generally held lower levels of defensive chemicals, while male and female leaves were similar in nutrients like nitrogen.17Oikos. Sex‐biased herbivory: a meta‐analysis of the effects of gender on plant‐herbivore interactions Insects seem to favor males for weaker defenses rather than better food. Female poplars ramped up bitter defensive compounds more strongly when chewed, and suffered less damage in the field.18Science of the Total Environment. Sex-specific interactions affect foliar defense compound accumulation and resistance to herbivores in Populus cathayana In two willows, though, the slow-growing males were better defended and less eaten than females.19Forests. Sex-Related Differences in Growth, Herbivory, and Defense of Two Salix Species In those willows, bigger plants were eaten more and defended less, suggesting the trade-off between growth and defense, more than sex itself, may decide which sex gets eaten more.
Damage shows as ragged holes, rolled leaves or skeletonized patches, and it appears on males more often on average, not always. If a male and female of the same shrub grow side by side, check the male first when scouting for caterpillars or beetles. Some chewing on a male is normal and not by itself a reason to spray.
How Female Plants Shape the Wildlife Around Them
Birds eating berries on female junipers drop seeds of other berry plants beneath them, so more seedlings of those plants sprout under female than male junipers.20Journal of Vegetation Science. Frugivorous birds mediate sex‐biased facilitation in a dioecious nurse plant Birds spreading mistletoe visited fruiting female trees about twice as often as males, and over half of female host trees were infected with mistletoe, against a quarter of males.21Ecology. FEMALE-DIRECTED DISPERSAL AND FACILITATION BETWEEN A TROPICAL MISTLETOE AND A DIOECIOUS HOST In some figs, female trees give off a distinct scent that helps seed-spreading animals find ripe fruit.22Functional Ecology. The chemical ecology of seed dispersal in monoecious and dioecious figs
A female holly or juniper in fruit can draw flocks of birds all winter, and you can expect self-sown seedlings of other shrubs beneath it. Males of the same species attract far fewer fruit-eating birds.
Berries that feed birds also drop on paths and lawns, and the birds may carry parasitic plants like mistletoe to the trees they favor. A female tree in a public space brings more mess but more wildlife.
Can a Plant Change Sex
Hormones tip the balance. In many plants, ethylene pushes flowers toward female and gibberellin toward male.23PubMed. Integrative control of plant sex determination: Genes, hormones, and environment In cucumber, gibberellin promotes male flowers partly by changing how the plant responds to ethylene.24PubMed Central. Transcriptomic Analysis Implies That GA Regulates Sex Expression via Ethylene-Dependent and Ethylene-Independent Pathways in Cucumber (Cucumis sativus L.) Stress, temperature and day length shift these hormones, so they can change the mix of flowers on some plants. A plant that makes both flower types, like cucumber, may produce more male or female flowers as conditions change. The shift shows up in flowers that form afterward; earlier ones stay as they were.
Growers flip female cannabis on purpose. Blocking ethylene with sprays such as silver thiosulfate makes female plants grow male flowers.25PubMed Central. Optimized guidelines for feminized seed production in high-THC Cannabis cultivars Three sprays a week apart turned most hemp flower clusters fully male, with top clusters at least 95% converted.26HortTechnology. Foliar Sprays of Silver Thiosulfate Produce Male Flowers on Female Hemp Plants Treated cannabis flowers switched sex at average rates above 80%.27PubMed Central. Sex‐specific ethylene responses drive floral sexual plasticity in Cannabis sativa Pollen from these converted females carries only female genes, so their seed grows into all-female plants.28HortTechnology. Foliar Sprays of Silver Thiosulfate Produce Male Flowers on Female Hemp Plants This is how ‘feminized’ seed is produced.
Female cannabis can also grow male flowers on its own. Stress like light leaks, heat or long delays at harvest can push some plants to form pollen sacs, which can fertilize the crop and fill buds with seeds. Checking flowering plants regularly and removing stray pollen sacs early prevents that.
None of this changes the plant’s chromosomes; only its flowers change. A strictly separate-sex plant does not turn into the other sex, and most garden plants like holly or kiwi will not switch at home. A ‘self-fertile’ variety was bred that way, not converted by care.
Do You Need Both Male and Female Plants
Fruit depends on the right mix. In a model of kiwi orchards, yield peaked when about two-thirds of flowers were female.29PubMed Central. Orchard layout and plant traits influence fruit yield more strongly than pollinator behaviour and density in a dioecious crop When nearly all flowers were female, only about 20% set fruit for lack of pollen.30PubMed Central. Orchard layout and plant traits influence fruit yield more strongly than pollinator behaviour and density in a dioecious crop Good yields also need males spread through the planting, flowering at the same time, and enough pollinating insects.31PubMed Central. Spatiotemporal Variation in Pollination Deficits in an Insect-Pollinated Dioecious Crop A female holly or kiwi with no male in range will flower but stay bare. That result comes from a model of commercial orchards, so a home gardener should read it as a hint that females can far outnumber males, not a strict recipe.
For home gardens, one male holly is commonly enough for several females within a short distance, and kiwi growers often plant one male vine for several females. Choose a male whose flowering time matches your female variety. A neighbor’s male plant may already be pollinating yours.
Sometimes one sex is the crop. Female cannabis flowers held far more CBD and THC than male flowers, with CBD nearly 17 times higher.32PubMed Central. Comparative analysis of gene expression and metabolites in female and male Cannabis sativa flowers Cannabis and hemp growers therefore usually remove males to keep female flowers seedless. Asparagus beds of all-male plants give more spears and few or no weedy seedlings, and male ginkgo avoids the smelly fallen seeds of females. The trade-off with male trees is pollen.
Do Male Trees Make Pollen Allergies Worse
Planners often favor male trees because females drop fruit, seeds and pods.33the Guardian. How urban planners A 1949 US farm guide advised planting only male street trees to avoid seed nuisance.34Office for Science and Society. Is “Botanical Sexism” Really to Blame for Increased Pollen Allergies in Urban Cities? After Dutch elm disease, male ash and maple were recommended as replacements, adding pollen to cities.35PubMed Central. Strong variations in urban allergenicity riskscapes due to poor knowledge of tree pollen allergenic potential Male street trees are also often clones, so a few varieties dominate a city’s pollen.36PubMed Central. Strong variations in urban allergenicity riskscapes due to poor knowledge of tree pollen allergenic potential
Whether this drives rising urban allergies is contested.37Office for Science and Society. Is “Botanical Sexism” Really to Blame for Increased Pollen Allergies in Urban Cities? Estimates of how allergenic each tree’s pollen is vary widely.38PubMed Central. Strong variations in urban allergenicity riskscapes due to poor knowledge of tree pollen allergenic potential Male trees add pollen but are likely one factor among several.
If you have allergies, favor female or insect-pollinated trees of low-allergy species when planting near your home, keeping in mind that female trees of wind-pollinated species can still be exposed to pollen from males nearby. Labels saying ‘seedless’ or ‘sterile’ usually mean male, which still sheds pollen. Separate-sex trees like ash, maple, poplar and willow release wind-blown pollen in spring.