The genus Bidens includes both annuals and perennials, and the answer for any particular plant depends on which species you have and where you’re growing it. With roughly 230 to 240 recognized species spread across tropical and temperate zones worldwide, Bidens spans a remarkable range of life cycles, from frost-tender herbs that die after one season to woody shrubs that persist for years. The garden varieties sold at nurseries add another layer of confusion, since most are technically perennial plants marketed and grown as annuals.
A Genus With Many Life Strategies
Bidens belongs to the daisy family (Asteraceae), and its species have colonized habitats on every continent except Antarctica. A comprehensive review of the genus documented between 230 and 240 species, making it one of the larger groups within its plant family.1PubMed Central. Bidens pilosa L. (Asteraceae): Botanical Properties, Traditional Uses, Phytochemistry, and Pharmacology That diversity translates directly into varied life histories. Some species complete their entire life cycle in a single growing season and die after setting seed. Others overwinter as root systems and resprout the following year. A handful of island-endemic species have even evolved into woody shrubs and vines that live for many years.
This variety means there is no single answer to “annual or perennial?” for the genus as a whole. Instead, the life cycle depends on the species identity, the local climate, and sometimes whether a frost arrives before the plant finishes setting seed.
Garden Bidens You Buy at the Nursery
If you’re asking this question because you just picked up a pot of yellow or pink Bidens at a garden center, you almost certainly have a cultivar of Bidens ferulifolia or a closely related hybrid. These plants are perennial by nature, surviving winter in frost-free climates. In USDA hardiness zones 9 through 11, they can persist year after year, flowering almost continuously. In cooler zones, however, they have zero frost tolerance and die at the first hard freeze. That is why garden labels and seed catalogs typically describe them as “tender perennials grown as annuals.”
For practical gardening purposes, treat nursery Bidens as an annual if you experience winter freezes. You can overwinter them indoors in a bright window or take stem cuttings in late summer, but leaving them in the ground through a frost will kill them. In mild-winter regions, they may surprise you by returning the next spring, sometimes vigorously enough to need cutting back.
Research on pollinator visitation to garden Bidens cultivars has shown real differences among named varieties. In one study, the cultivar ‘Pretty in Pink’ attracted significantly more pollinator visits per minute than ‘Bee Happy Red Imperial,’ a difference explained by higher nectar volume and greater sugar concentration in the flowers of ‘Pretty in Pink.’2Journal of Economic Entomology. Variation in pollinator visitation among garden cultivars of marigold, portulaca, and bidens So if you’re choosing cultivars partly to support bees and butterflies, the specific variety matters as much as the species.
Wild and Weedy Bidens
Outside the garden world, many Bidens species are better known as agricultural weeds. The most widespread is Bidens pilosa, sometimes called black-jack or beggar-ticks, which grows across tropical and temperate regions on every inhabited continent. This species illustrates the annual-versus-perennial confusion perfectly: some references describe it as a perennial herb, while field studies in temperate regions classify it as a summer annual. Both descriptions are correct, depending on location. In tropical and subtropical climates where temperatures stay mild year-round, B. pilosa can persist as a short-lived perennial, producing flowers and seeds continuously. In regions with cold winters, it behaves as a strict annual, dying back completely and relying on its prolific seed output to re-establish the following year.
That seed output is staggering. B. pilosa has been documented producing several generations within a single year, with a high achene production rate that helps explain why it ranks among the world’s most aggressive invasive plants.3PubMed Central. The Invasive Mechanisms of the Noxious Alien Plant Species Bidens pilosa Growth studies comparing B. pilosa to other invasive species found it had a faster relative growth rate and better colonizing ability, traits that let it outcompete native vegetation in newly invaded areas.4PLOS ONE. Potentials of invasive Bidens pilosa, Conyza bonariensis and Parthenium hysterophorus species based on germination patterns and growth traits
Other wild Bidens species are unambiguously annual. Bidens tripartita (three-lobe beggarticks) and Bidens cernua (nodding beggarticks) are summer annuals that grow in wet mudflats and pond edges across North America and Eurasia. They germinate in spring, flower in late summer, set seed, and die. Their persistence from year to year depends entirely on the seed bank they leave behind in the soil.
How Climate Determines Which Label Applies
The annual-or-perennial question often comes down to frost. Many Bidens species are tropical or subtropical in origin, and their tissues cannot tolerate freezing. In regions where winter temperatures drop below about 5°C for extended periods, even species that would otherwise live for years get killed outright. The plant’s response to cold determines whether it persists as a perennial or functions as a de facto annual in any given location.
Several research groups have studied cold tolerance in invasive Bidens species, and the results help explain why some species push into cooler regions while others stay put. When B. pilosa and the native Chinese species B. biternata were grown at low temperatures (around 10/5°C day/night), B. pilosa showed a smaller drop in growth rate and better maintenance of its photosynthetic machinery. Higher levels of protective proteins in B. pilosa appeared to help it maintain physiological function in the cold.5Biological Invasions. Winter low temperature disturbance in the southern subtropics of China promotes the competitiveness of an invasive plant
A closely related species, Bidens alba, showed an even broader tolerance. Compared to native B. biternata, B. alba maintained greater biomass and faster growth under both cold and heat extremes, suggesting it can handle a wider range of climates.6Nordic Journal of Botany. Effects of extreme temperatures on the growth and photosynthesis of invasive Bidens alba and its native congener B. biternata Under chilling stress specifically, B. alba maintained greater physiological stability and better coordination of its internal defenses compared to B. biternata.7Flora. Whole-plant coordination drives cold tolerance in an invasive Bidens alba: Organ-specific resource allocation and defense mechanisms This kind of resilience is exactly what allows a tropical perennial to behave like a perennial in marginal climates rather than getting knocked back to an annual cycle by winter stress.
For gardeners, the takeaway is straightforward: if you live somewhere that gets frost, your Bidens will act as an annual regardless of its genetic potential. If you live in a mild coastal or subtropical climate, many species and cultivars will come back year after year.
Seeds and Self-Renewal
Even species that function as strict annuals can give the impression of being perennial because they reseed so reliably. Bidens seeds (technically achenes, the small barbed fruits that stick to clothing and animal fur) germinate readily, and in many species they need nothing more than light and moisture to sprout. Research on B. pilosa germination showed that seedling emergence was highest when seeds sat on the soil surface, reaching about 71%, while no seedlings emerged from seeds buried 8 cm or deeper.8PubMed Central. Seed germination ecology of Bidens pilosa and its implications for weed management That preference for surface germination means undisturbed soil, such as in no-till farming systems, provides ideal conditions for Bidens to re-establish itself each year without any human help.
The seed bank itself varies between species. Bidens tripartita can build up a persistent seed bank in the soil, with viable seeds surviving at least 20 months of burial. By contrast, Bidens cernua seeds were all dead after the same burial period.9Aquatic Botany. The role of temperature in the regulation of dormancy and germination of two related summer-annual mudflat species This difference matters for anyone trying to manage these plants: B. tripartita can bounce back from a seedbank left over from a previous year, while B. cernua is more dependent on fresh seed dispersal each season.
For gardeners who enjoy self-sowing annuals, this prolific seed production can be a feature rather than a bug. In mild climates, Bidens ferulifolia and its hybrids may scatter seeds that germinate the following spring, creating the appearance of a perennial planting without any deliberate effort. Deadheading spent flowers prevents this if you’d prefer not to have volunteer seedlings.
Managing Bidens as a Weed
In agricultural settings, the annual life cycle of Bidens species is both their weakness and their strength. Because they depend on seed production to survive, preventing seed set in a given year can dramatically reduce next year’s population. Mowing B. pilosa at 14 and 25 days after crop emergence prevented it from producing seeds, giving effective control of the weed in organic corn cultivation.10Planta Daninha. Management of Bidens pilosa and Commelina benghalensis in organic corn cultivation under no-tillage
Chemical control has a narrow window. Herbicides including glufosinate, glyphosate, and paraquat provided acceptable control (above 90% kill) when applied at the four-leaf stage of B. pilosa, but none of them achieved that level when plants had reached the six-leaf stage.8PubMed Central. Seed germination ecology of Bidens pilosa and its implications for weed management That rapid growth from vulnerable seedling to herbicide-tolerant plant underscores why timing matters more than product choice when dealing with annual Bidens weeds. Miss the window by a couple of weeks and you’re essentially waiting for the next generation.
The combination of surface-dependent germination and fast growth also explains why Bidens weeds thrive in no-till and conservation agriculture systems. Leaving the soil undisturbed keeps seeds at the surface where they germinate best, and the absence of tillage means no mechanical disruption of young seedlings. Farmers using these systems often need to integrate cover crops or targeted early-season herbicide passes to keep Bidens from dominating.
The Hawaiian Outliers
The most dramatic exception to the “annual or short-lived perennial” pattern exists on Pacific islands. The Hawaiian archipelago is home to a radiation of Bidens species that have evolved into woody shrubs and scrambling vines, some living for many years. These plants look nothing like the delicate garden annuals sold on the mainland. They have thick stems, indeterminate growth (meaning they keep growing rather than stopping after flowering), and they occupy forest understory niches that would be unusual for any mainland Bidens.
Phylogenetic work using DNA sequences revealed that these Polynesian Bidens descended from a group of Latin American herbaceous species with determinate growth, not from the already-woody vines found in Central American forests. That means the woodiness and long-lived perennial habit evolved independently on the islands, a classic case of adaptive radiation into open ecological niches.11Systematic Botany. ITS Base Sequence Phylogeny in Bidens (Asteraceae): Evidence for the Continental Relatives of Hawaiian and Marquesan Bidens In evolutionary terms, the ancestor that reached the islands was likely an annual or short-lived perennial herb, and island conditions favored the evolution of a longer-lived, woody form over time.
Many Hawaiian Bidens species are now endangered due to habitat loss, invasive herbivores, and competition from other introduced plants. They represent a striking example of how flexible the Bidens life cycle can be given enough evolutionary time and the right ecological pressures.
Climate Change and Shifting Ranges
The geographic boundaries that currently determine where Bidens species act as perennials versus annuals are themselves shifting. Climate modeling for B. pilosa projects a decline of suitable habitat in tropical regions alongside an expansion into temperate zones as winters become milder.12PubMed Central. Projecting global shifts in the invasive potential of Bidens pilosa L. under climate change using species distribution models In practical terms, areas that currently experience hard winter freezes may see B. pilosa surviving through winter in the coming decades, effectively shifting its behavior from annual to perennial without any genetic change in the plant itself.
Not all Bidens species benefit from warming, though. Bidens macroptera, a culturally significant species in Ethiopia sometimes called Adey Abeba, faces a different trajectory. Modeling of its future habitat suitability found declines across all projected climate scenarios, raising the possibility of local extinction in parts of its native range.13PubMed Central. Modeling the Spatiotemporal Habitat Suitability Distributions of Cultural Keystone Bidens macroptera (Adey Abeba) Under Climate Change Scenarios in Ethiopia The contrast between an invasive species expanding its range and a native species losing habitat is a reminder that “Bidens” covers an enormously varied group of plants with very different ecological fortunes.
Traditional and Medicinal Uses
One reason Bidens pilosa appears in so many references and across so many regions is its long history of use in traditional medicine. The plant has been documented in folk medicine traditions across Africa, Asia, and the Americas, where it has been used for a wide range of ailments. A pharmacological review catalogued its traditional applications and the chemical compounds responsible for its biological activities, noting properties that range from anti-inflammatory to antimicrobial.1PubMed Central. Bidens pilosa L. (Asteraceae): Botanical Properties, Traditional Uses, Phytochemistry, and Pharmacology
In some tropical regions, B. pilosa is actively cultivated or at least tolerated in kitchen gardens as a leafy green vegetable. The young leaves are cooked and eaten in parts of East Africa and Southeast Asia. This dual status as both weed and food plant is part of what makes the species so widely distributed: it thrives in disturbed soil around human settlements, which is also where people are most likely to notice, harvest, and inadvertently spread it. Whether you’re pulling it out of a cornfield or adding it to a stir-fry, the plant’s fast annual growth cycle and prolific seeding ensure there will always be more of it next season.