Yarrow: Nobody Quite Agrees What You're Buying

A field guide to Achillea millefolium, the flat-topped white perennial of native plant sales and European meadows. Why the major plant authorities can't agree what the name covers, and why one federal fact sheet gives the most native-sounding label on the bench to the introduced plant.

About the Plant

We'd hand yarrow to a beginner without a second thought. Flat white flower heads on knee-high stems, foliage so finely cut it reads as a haze from ten feet away, no interest in being fussed over, and a flowering season long enough that you stop noticing when it started.

It's also the hardest plant in the native aisle to buy knowing what you've got, and the problem starts before the plant reaches the nursery. The major plant authorities draw the boundaries of the name Achillea millefolium differently, and at least one federal document uses the most native-sounding common name in the trade for the European plant.

What You're Looking At

Flora of North America's description opens: perennials, 6 to 65+ cm, usually rhizomatous, sometimes stoloniferous (Flora of North America Editorial Committee, 2006). Rhizomatous means it travels by underground stems; stoloniferous means it sometimes runs along the surface too. The leaves are the giveaway, divided and redivided until each one looks like a small fern frond. The flower heads are crowded into flat or slightly domed clusters, usually white, sometimes pink in wild populations. If you want that flat top taken apart under a hand lens, the Flower Library entry on the corymb does it with this plant.

Height is where the sources part company, and you want to know that before you plan a bed. Those 6 to 65+ cm work out to about 2.4 to 26+ inches. The Forest Service's account gives 11 to 40 inches (30 to 100 cm) and calls it a perennial forb, meaning a non-woody flowering plant, with extensive rhizomes (Aleksoff, 1999). Plan on something knee-high in flower and treat any single published number with suspicion.

Habitat tolerance is the easy part. Flora of North America's list runs from pasture and meadow to roadside, streamside and woodland, takes in waste ground, and covers dry or sandy soils at one end and damp, clayey or salty ones at the other, at any elevation from sea level to 3,600 m, about 11,800 feet (Flora of North America Editorial Committee, 2006).

Three Authorities, Three Classifications

Flora of North America treats Achillea millefolium as one species and files the western names as synonyms of it, names it treats as duplicates instead of plants in their own right, among them var. borealis, var. californica, var. lanulosa, var. occidentalis and var. pacifica. Its discussion lays out the problem. The plant's form varies widely. Botanists have met that either by keeping one species and dividing it into varieties or by cutting it into separate species outright, and North American specimens have carried at least fifty-eight names between them (Flora of North America Editorial Committee, 2006).

Kew's Plants of the World Online answers differently. It treats Achillea borealis Bong. as an accepted species whose native range it gives as "Russian Far East to NW. Mexico", and lists among its accepted varieties Achillea borealis var. californica (Plants of the World Online, 2026a). For Achillea millefolium it gives a native range of "Greenland, Subarctic & Temp. Eurasia", and records the plant as introduced into a long list of places including Massachusetts, New Jersey, New York, Pennsylvania and Texas (Plants of the World Online, 2026b).

Both of those range lines are Kew's own wording, printed in its abbreviated house style. NW. is northwest and Temp. is temperate, and the Eurasian label covers Greenland plus subarctic and temperate Europe and Asia, south as far as the Mediterranean, southwest Asia and the Himalaya in Kew's country list, with no part of the Americas in it but Greenland. Bong. is doing a different job. It's the naming authority: August Gustav Heinrich von Bongard, who published Achillea borealis in 1832 (International Plant Names Index, 2026), in the way the L. after Achillea millefolium stands for Linnaeus.

USDA PLANTS, the Department of Agriculture's own database, keeps one species with twelve accepted varieties and splits native from introduced between them. Its records give var. californica, var. occidentalis and var. borealis among those native to the lower 48 states, and var. millefolium as introduced there (U.S. Department of Agriculture, Natural Resources Conservation Service, n.d.-b). So the Californian plant that USDA files as a variety of millefolium, Kew files as a variety of a different species.

The Forest Service, also part of the Department of Agriculture, reports a different list. Its 1999 species review states that most authorities do not recognize any ranks below the species here, then adds "however, Kartesz recognizes the following varieties" and relays eight of them (Aleksoff, 1999).

So Flora of North America and Kew disagree about where the species ends, and two parts of one federal department report different variety lists. Careful sources can disagree like this when the group is hard. The Forest Service, citing Cronquist and colleagues, puts the difficulty on the record: the variation within the species "has frustrated all efforts to organize an intraspecific taxonomy on a circumboreal or even a strictly North American basis" (Aleksoff, 1999). In plainer words, the plant varies in shape, in where it grows and in what it grows in, all at once, and attempts to sort it into named groups below species, around the northern hemisphere or within North America alone, have run aground on that.

The Common Name Does Two Jobs

The USDA Natural Resources Conservation Service publishes a plant fact sheet on western yarrow, the native western North American plant. Under the heading Weediness it tells the reader not to confuse western yarrow with "the introduced, invasive plant, common yarrow (Achillea millefolium var. millefolium)". It puts that plant's origins in Eurasia, continental Europe and the islands of Scandinavia, and separates it from the western native on four counts: it stands taller, grows more aggressively, behaves more weedily, and comes into flower and ripens its seed later in the season (U.S. Department of Agriculture, Natural Resources Conservation Service, n.d.-a).

In that document, the name common yarrow belongs to the European variety. It's also about the most native-sounding name a plant tag can carry.

Other USDA documents use the phrase the other way. The Forest Service species review cited throughout this entry uses common yarrow for the whole species, native phases included (Aleksoff, 1999), and so does the NRCS plant guide for the species (Mann et al., 2022). Flora of North America gives Common yarrow as the species' English name too (Flora of North America Editorial Committee, 2006). One fact sheet uses common yarrow for a single introduced variety; the rest use it for everything. So a label reading common yarrow tells you less than it appears to.

The Experiment in the Sierra

The reason origin matters to a garden was shown eighty years ago, on a transect that runs right past us. A transect is a line of study sites laid out across changing conditions; this one ran across central California, from the coast over the Sierra to the Great Basin.

Clausen, Keck and Hiesey, of the Carnegie Institution's Division of Plant Biology, carried fourteen key yarrow populations through their three gardens. The plants were raised at Stanford from wild-collected seed, and the roughly thirty individuals of each population used in the transplant were picked from a random sample of sixty such seedlings. In 1942, as they put it, "approximately 30 individuals of each of fourteen populations were divided into three parts and planted in the gardens at Stanford, Mather, and Timberline" (Clausen, Keck, & Hiesey, 1948). Stanford sat at 30 m, about 100 feet. Mather was on the Sierra Nevada's western slope at 1,400 m, about 4,600 feet. Timberline was just over the crest in Slate Creek Valley at 3,050 m, roughly 10,000 feet, near the tree line.

A climatic race is a population shaped by the climate it grew up in, distinct enough to behave differently once it is moved. Under the extreme conditions at Timberline, they wrote, "the coastal races were almost eliminated after the first winter, and none flowered." A long frosty spell in 1946 then tested the mountain races. Of the plants raised from Tenaya Lake seed, high in the Sierra, 79 percent had undamaged flower clusters through it, against 35 percent of the plants from Yosemite Creek, and most of the Tenaya Lake plants ripened seed at Timberline nearly every year (Clausen, Keck, & Hiesey, 1948).

Their own summary of the design: the three stations "serve as a climatic sieve by which the populations may be sorted into distinguishable ecological units" (Clausen, Keck, & Hiesey, 1948). They describe the first step: "When climatic races from many diverse environments are brought into one garden, we see their genetic differences expressed under one set of conditions." The sieve is the three gardens together, each showing which races do best at its altitude.

In the taxonomy those authors used, the Californian plants on that transect were not Achillea millefolium. Summarizing their own earlier treatment, they wrote that "A. millefolium L. is considered to be native only in the Old World" (Clausen, Keck, & Hiesey, 1948), which left the European populations as the only true millefolium in the experiment. At Timberline, they recorded, "the California forms develop vigorously with abundant flowering, and the Lapland form remains a low, barely surviving vegetative mat" (Clausen, Keck, & Hiesey, 1948). The California forms in that sentence are the alpine ones.

So at Timberline most of the Lapland plants came through the winters but almost never flowered, while the Californian races from the coast were the ones the first winter almost eliminated.

This study gets repeated loosely, and three points need correcting. Clausen, Keck and Hiesey did not invent the ecotype, the idea that a widespread species breaks into locally adapted races, and they say so in their own first paragraph: these races "were first studied experimentally by Turesson (1922), who named them ecotypes, a term and concept universally accepted" (Clausen, Keck, & Hiesey, 1948). Their own term for the three gardens is transplant stations. And the differences did not simply hold steady from garden to garden, since the volume records reversals where a population flowers later than another at Stanford and earlier at Mather. What held is their own formulation: "although the individuals and populations vary, the races are statistically and reactionally distinct" (Clausen, Keck, & Hiesey, 1948).

If you're following this up, the yarrow work is Volume III of the series, issued as Carnegie Institution of Washington Publication 581, with a first printing in 1948; the copy we read is the third printing. Publication 520 of 1940 is Volume I of the same series, a different book.

So Can You Tell by Looking?

Mostly not.

North America carries both native and introduced forms of the plant, which the Forest Service calls phases, and the two hybridize. The same review adds, on the authority of the sources it cites, that they differ mainly in chromosome number and are difficult to tell apart by their form (Aleksoff, 1999). Chromosome number isn't something you can see in a garden, and the two phases cross.

The sources do record visible differences. In a different section, that Forest Service review draws a contrast: the typical European plant is hexaploid, carrying six sets of chromosomes, and holds its leaves flat, while the native forms are mostly tetraploid, with four sets, and set their narrow leaf segments on several planes at once, so the leaf reads as a three-dimensional thing (Aleksoff, 1999). The NRCS fact sheet describes western yarrow's leaves as densely hairy and the introduced plant's as smooth or only sparsely hairy (U.S. Department of Agriculture, Natural Resources Conservation Service, n.d.-a). And Flora of North America lists the physical features botanists have reached for when trying to split these populations up: how much felty hair a plant carries and how long it keeps it; the color of the margins of the phyllaries, the small bracts sitting under each flower head; the shape of the flower clusters; and how finely the leaves are cut. It then ties two of them, phyllary color and hairiness, to latitude, elevation and extreme habitats, and says these are only trends (Flora of North America Editorial Committee, 2006).

So the difference is real and leaves visible traces, and the Forest Service still calls the two difficult to tell apart by form. If someone tells you they can spot European yarrow across a nursery bench, they're telling you about their confidence more than about the plant.

What the Choice Costs You in Bees

If you can't reliably tell native from introduced, it's fair to ask whether any of this changes what you do on a Saturday. On the cultivar question, at least two studies have measured it.

Hayes and colleagues ran a common garden experiment, with every plant grown side by side under the same conditions, in Corvallis, Oregon, over three field seasons from 2020 to 2022, comparing the pollinators on Pacific Northwest native plants with those on their cultivars. They collected and observed bees, butterflies and syrphid flies, which are hoverflies (Hayes et al., 2025). Yarrow was in it: wild-type Achillea millefolium set against two hybrid cultivars, Achillea × 'Moonshine' and Achillea × 'Salmon Beauty', with 'Moonshine' added a season late, in 2021. Their Table 2 gives observed species richness, the number of different species recorded, of 21 on the wild type, 15 on 'Moonshine' and 14 on 'Salmon Beauty', and in the bee column alone, 16 species on the wild type against 8 on each cultivar. Across all their study plants, they report, the native plants always had greater bee richness than their cultivars.

The table has limits worth knowing. First, it also gives Chao1 figures beside the observed totals, the authors' statistical estimate of total species richness, and those run 41 for the wild type, 20 for 'Moonshine' and 41 for 'Salmon Beauty'. On the estimate, 'Salmon Beauty' is level with the wild plant, and the authors note it as one of two cases where a cultivar's estimated richness matched or beat its native. The bee comparison, 16 against 8 and 8, is observed richness; the table's Chao1 figures cover all pollinators, not bees. Second, the study sampled bees, butterflies and hoverflies only, so 21 is not a count of everything that visited. Third, the plots were watered as needed through each growing season, and 'Moonshine' had one season fewer than the wild plant. Fourth, on visit counts, as opposed to species, the yarrow group was mixed: the authors report that its preferences varied by pollinator group (Hayes et al., 2025).

The second study ran at two field sites in northern Vermont. Annie White set wild-type Achillea millefolium against 'Strawberry Seduction', a cultivar of the same species, and counted 1,414 pollinator visits to the wild type against 119 to the cultivar (White, 2016). Pollinators as a whole, and the group the study calls other native bees, showed a strong preference for the wild type; flies showed no preference either way. The wild plant also carried more flowers, and allowing for that did not change the result.

Neither garden was in California and they measured different things, but both point the same way. On bee species in Oregon, and on visits from native bees in Vermont, the plain plant came out ahead of the cultivars.

The Nursery Bench

What gets said about these plants' ancestry is thin, and the institutions don't agree. Take 'Moonshine'. Cambridge University Botanic Garden gives it as a hybrid of A. clypeolata and A. 'Taygetea' raised by Alan Bloom in 1954 (Cambridge University Botanic Garden, n.d.). A United States plant patent for a later introduction describes its pollen parent as Achillea millefolium 'Moonshine' (Stemkens, 2017), which files the plant under a different species again. And the putative parent turns up as a hybrid, A. × taygetea, in the Chicago Botanic Garden's trial report (Hawke, 1994) and as a cultivar, 'Taygetea', at Cambridge. For a question about what you're actually buying, that disagreement among institutions is a harder fact than any single parentage claim.

The same Chicago report traces 'Salmon Beauty', one of the two cultivars in the Oregon trial, to the Galaxy hybrids, which came from a cross between Achillea millefolium and A. × taygetea (Hawke, 1994).

Summer Pastels has the cleanest record. All-America Selections lists Achillea Summer Pastels F2 as a 1990 Flower Winner, raised from seed, filed under Achillea millefolium, from the breeder K. Sahin, Zaden B.V. (All-America Selections, n.d.). It matters here because 'Strawberry Seduction', the cultivar in the Vermont study, came from repeated selections out of that seed strain (White, 2016).

None of this makes the cultivars bad plants. 'Moonshine' is a good garden plant and we won't pretend otherwise. It does mean the label alone won't settle what you're buying, and the bee numbers above are the strongest reason to walk past the named ones.

Water: What's Measured and What Isn't

Yarrow gets recommended as a low-water plant, and the rating behind that in California rests on consensus, not measurement.

The 1994 edition of WUCOLS, California's reference for landscape water use, rates yarrow low-water in its North-Central Coastal region, whose listed cities include San José and Oakland. Its Method section says what the ratings are: the ratings are "subjective evaluations" made to a standard format, resting on the experience and observations of the people taking part alongside whatever research was to hand. Further on, under Making Water Needs Assignments, it records that each species landed in a single water category "as determined by consensus of each regional committee". The numeric bands behind those categories were extrapolated from figures worked out for related farm crops, citrus, walnuts and cherries among them, and for some landscape species (Costello & Jones, 1994). It's an expert panel's judgment, calibrated partly against orchard trees: a reasonable basis for a planting decision, but not a measurement of yarrow.

Drought tolerance differs from one ecotype to the next, according to the Forest Service's southern California profile, which also finds the plant mostly in damp swales and meadows in the southern California lowlands (Montalvo et al., 2010). Whether your yarrow shrugs off August may depend on where its ancestors came from, and the tag won't tell you.

Practically: water it through its first dry season, then taper and watch.

It Spreads

Usually rhizomatous, sometimes stoloniferous: that is the first line of the description in Flora of North America (Flora of North America Editorial Committee, 2006). The Forest Service records extensive rhizomes (Aleksoff, 1999), and its southern California profile warns that in a garden the plant can turn invasive, so it needs placing with care (Montalvo et al., 2010).

The clearest illustration comes from a trial. The Chicago Botanic Garden evaluated 42 kinds of cultivated yarrow over four years, and the spreading kinds grew so fast that their widths couldn't be measured past the first season. Plants had gone in 18 to 24 inches (46 to 61 cm) apart, and by the second season the space between them was filled. The report's own explanation: "widths were not routinely recorded due to the vigorous spreading nature of the plants" (Hawke, 1994). Not every kind spread; the report sorts its plants into spreading and clump-forming.

Site it where a slow traveler is welcome, not in a tight mixed border you've planned to the inch. That trial ran in Chicago on beds that were fertilized every year and kept moist by the irrigated turf around them.

In the wild the picture is looser. The Forest Service records that the plant grows in a somewhat scattered way and seldom forms pure stands larger than 5 square meters, about 54 square feet (Aleksoff, 1999).

Planting It This Autumn

Yarrow fits the pillar's case for autumn planting. Put a container plant in the ground in October or November and the winter rains do the establishment for you. Full sun: the Forest Service records that across its range the plant usually occupies dry, open sites, in habitats of many kinds, and that it is intolerant of dense shade (Aleksoff, 1999). For cold, NC State Extension lists USDA zones 3a to 9b (North Carolina State University Extension, n.d.) and Nebraska Extension lists 2 to 9 (University of Nebraska-Lincoln Extension, n.d.).

On seed set, the Forest Service's southern California profile calls it generally an obligate outcrossing species and self-incompatible, meaning a flower needs pollen from another plant to set seed, and notes that seed set without fertilization, called apomixis, has been found in related species of the complex in Europe, though how far it goes is not known (Montalvo et al., 2010). Plant several, and more than one clone if the nursery can manage it. And because it travels, give it an edge it can meet: a path or a strip of gravel does more for a tidy bed than any amount of later editing.

Buy plants for a first planting instead of sowing seed, because the germination guidance conflicts. The NRCS plant guide for the species says the seed needs a month of cold stratification and direct sunlight to germinate (Mann et al., 2022). The southern California profile reports USDA fact sheets saying western North American seed needs no treatment at all, and Stevens and colleagues reporting that seed from some sources may need up to two weeks of cool, moist stratification (Montalvo et al., 2010). The same profile expects seed dormancy to differ by source population.

Handling It

Yarrow can cause contact allergy, and it is one of the plants in the Compositae (daisy family) mix that German dermatology clinics used in their standard patch-test series (Salapovic et al., 2013).

Salapovic and colleagues measured the allergenic sesquiterpene lactones, the main contact allergens in the daisy family, in the five plant extracts of that mix, and set the results against patch-test results from 125 patients who reacted to the family. The two extracts richest in those compounds, feverfew and tansy, produced the most patch-test reactions; the two poorest in them, German chamomile and yarrow, produced significantly fewer. Their measured figures put tansy extract at 11 percent allergenic sesquiterpene lactones, arnica at 3 percent and yarrow at 2 percent (Salapovic et al., 2013). If you already know you react to daisies, chrysanthemums or feverfew, wear gloves when you cut a lot of yarrow back.

Yarrow is also linked with light sensitivity. A 2021 dermatology review includes Achillea millefolium in its compilation of photosensitizing drugs (Hofmann & Weber, 2021), and we went looking for the clinical evidence behind entries like that. I searched PubMed and Europe PMC in October 2026, pairing Achillea, millefolium and yarrow with phototoxic, photoallergic, photosensitivity, photodermatitis and related terms, and found no case report of a light reaction to yarrow on its own.

The evidence that did turn up points two ways. In a Brazilian series of 21 patients with chronic actinic dermatitis, a long-running light-sensitive skin condition, two reacted under light testing to a Compositae mix that includes yarrow (Scherrer et al., 2025). The European Medicines Agency's assessment report, on the other side, relays a 2001 source in which alcoholic extracts of the plant's dried leaves and stalks produced no phototoxic response in clinical testing; the same paragraph records that in provocation testing, patients reacted to a Compositae mix containing yarrow and to yarrow itself (European Medicines Agency, 2010).

The link that is documented runs through the allergy. An Australian case series puts it this way: "Compositae dermatitis may be complicated by chronic actinic dermatitis (CAD) which is associated with photosensitivity" (Punchihewa et al., 2022). That ties the documented light problem to people with daisy-family dermatitis, which is a narrower thing than the general warning that yarrow causes light sensitivity. This entry is not medical advice and gives none.

Sourcing

Buy it from a California Native Plant Society (CNPS) chapter nursery, and ask two questions:

• Is this wild-type, or a named selection?
• Do you know where the seed came from?

You can't answer the provenance question by looking at the plant. The Forest Service's southern California profile puts it plainly: farm-grown seed is on sale from the major seed companies, but "information about the source of the seeds is often obscure" (Montalvo et al., 2010). The same profile lists two yarrow seed releases, one collected in Montana and a source-identified one from collections in Washington, and adds: "We are not aware of any releases developed from California populations."

The CNPS Santa Clara Valley chapter runs its nursery at Hidden Villa in Los Altos Hills and sells through its plant sales and an online store (California Native Plant Society, Santa Clara Valley Chapter, n.d.); check the chapter's site for sale days. Ask there first. A chapter nursery is the likeliest place we know of to get a straight answer about where a plant came from.

If a nursery can't tell you, that's not unusual for this plant.

A Footnote for the Curious

The chromosome line for Achillea millefolium in Flora of North America lists counts of 18, 27, 36, 45, 54, 63 and 72, European material included (Flora of North America Editorial Committee, 2006). Every one is a multiple of nine, the full run from 18 to 72. The same treatment reports a school of botanists who see the group as native and introduced plants that have hybridized into diploid, tetraploid, pentaploid, hexaploid, septaploid and octoploid forms, all one variable species. Flora of North America itself treats the plant as one variable species.

The people who work on this group are direct about where it leaves them. Guo and colleagues open the discussion of their study of the group's family tree by restating the problem they set out to address: "at the polyploid level, species are difficult to define either by morphology or by molecular data" (Guo et al., 2012). The same paper describes the northern-hemisphere Achillea millefolium group as varying widely in both form and genetics, and as living across a broad range of conditions.

Clausen, Keck and Hiesey showed with three gardens that where a yarrow came from shapes how it grows. The label on the pot won't tell you where that was, so ask.

The Takeaway

Yarrow is worth growing and hard to buy precisely. Three major authorities classify it three ways, one USDA fact sheet gives the most native-sounding common name to the European variety, and squinting at the foliage won't reliably settle it: the Forest Service reports the two differ mainly in chromosome number and are hard to tell apart by form. Choose well anyway. Buy wild-type plants from a chapter nursery that knows where its seed came from, skip the named cultivars if you're planting for bees, put it in full sun in autumn, and expect it to be somewhere slightly different every year.