No matter what you
call them -- cornflowers, bachelor’s buttons, basket flower,
or the old-fashioned blue-bottle--members of the genus Centaurea
are wonderful additions to a garden. Even if they weren’t
great cut flowers, which they are, the blue color of the
species would make them desirable. They have been grown in
American gardens since Colonial times, primarily from seeds
brought over from Europe.
Most centaureas originated in Europe, where they still inhabit
fields and waysides today, but a few are native to the
Americas. They have been part of gardens for centuries, going
back to ancient times. In fact, the genus name, Centaurea
has its basis in Greek mythology. One of the centaurs, Chiron,
is said to have used the flower to heal wounds, including his
own, after battle. The most peaceful of the centaurs (who were
a warlike group of half man-half horse), Chiron is credited in
myth with teaching mankind about the healing powers of herbs.
In spite of that history, cornflowers weren’t as established
as medicinals as other herbs, perhaps in part because of
confusion with centaury (Centaurium, now known as Erythraea
centaurium), which has a similar name but very different
flower color. Both were thought to be beneficial for eye
ailments--understandable for cornflowers because of their blue
color. In the mid-1600’s, herbalists such as John Gerard and
Nicholas Culpepper included cornflower, or “blew-bottle,”
in their books on useful herbs. Culpepper claimed the dried
leaves could be used as a remedy against the poison of the
scorpion, if they were mixed in water with plantain or
comfrey. Modern herbalists don’t advocate that, but they do
consider a decoction of the leaves useful as an eye lotion.
What’s in a Name?
There are many species of centaurea, but the most readily
available as seeds or plants are Centaurea cyanus,
cornflower, or bachelor’s-button; C. americana,
basket flower; and C. montana, mountain bluet, or
Cornflowers are appropriately named--they grow wild in corn
fields in Europe and the United States and bloom basically
until the harvest season begins.
The term bachelor’s-button refers to the long-lasting
quality of the flower when it is cut and placed in the
buttonhole of a suit or shirt; decades ago, bachelors sported
the flower when they went courting. The origin of bluet in
mountain bluet is from France.
The blooms of basket-flower give it its name: Because of the
ray-like outer petals, the heads look as if they are set in a
Annual bachelor’s-buttons and basket-flowers begin to bloom
in late spring and continue through summer. C. americana,
an annual native to the south central and southeastern United
States, is hardy to Zone 4. Centaurea can tolerate low
temperatures of 41 degrees Fahrenheit.
Native to the mountains of Europe, mountain bluet flowers from
late spring to early summer. It is hardy to Zone 3 and
produces fringed, violet-blue flowers with deep purple
Also a member of the Centaurea genus is the well-known
bedding plant dusty miller. A perennial, C. cineraria
is grown for its grayish foliage, not its rather unattractive
purple flowers. Even though it is perennial to Zone 4, it’s
best to treat it as an annual; it doesn’t come through
winter looking very good.
Some species, which you won’t find for sale, are unwelcome
in gardens and fields because they are noxious weeds. Known
variously as knapweed and hurt sickle, they were introduced
from Europe, and they crowd out more desirable native plants.
Hurt sickle refers to the ability of the tough stems of the
plants to dull, and sometimes break, a farmer’s sickle back
in the days of hand-reaping. Knapweed comes from the rounded,
knobby flower—knap is an older English form of “knob.”
They are not plants for a garden—or anywhere else, for that
Flower and Plant Forms
Centaureas produce single and double, fringed blooms on plants
that range in height from 10 inches to 2-1/2 feet, depending
on the species or cultivar--basket flower can reach 4 feet in
height. The shape of the flower petals resembles that of
thistles, but the plants’ leaves do not have the spines of
the latter! The leaves are often an attractive gray-green.
Mountain bluet grows about two feet tall with an equal spread.
The flowers are usually lavender blue, but you may also find
plants with rose, pale yellow, or white blooms.
Tall and double-flowered forms are particularly valuable in a
Dwarf forms of centaurea, especially the Florence series and
the ‘Midget’ mixture, with their 10- to 20-inch height and
naturally compact, bushy growth habits, are good choices for
edging a garden or filling out a container. Colors include
violet, red, pink, lavender, blue, and white.
Growing from Seed
Centaureas are very easy to grow from seed started indoors or
out. The taller varieties, which are so useful in cutting
gardens, may not be readily available as plants at garden
centers and should be started from seed. Perennial mountain
bluet simply takes a little longer to germinate than the
annual kinds; started early enough, it may bloom the first
year it is planted.
According to the National Garden Bureau, you can sow annual
centaureas outdoors in late September in mild winter areas;
they will start to grow before the first fall frost (if any)
and will bloom earlier the following spring. In colder zones,
sow seeds in early spring as soon as the ground can be worked.
Sow perennials in early spring or fall.
- Because the seeds germinate readily, you do not need to sow
seed thickly. If you are sowing in spring, it’s a good idea
to make more than one sowing of the annuals because centaureas
are not long-blooming plants. Sow two to three times at two
week intervals to have flowers through summer. If you sow in
fall, plan to resow at least once the following spring.
- Sow seeds about 1/2 inch deep in any good garden soil.
Centaureas prefer slightly alkaline soil, but they are really
- Keep the seedbed moist until germination occurs—in 7 to 10
days for annuals, 2 to 3 or 3-1/2 weeks for perennials.
- Annual cornflowers perform best when they are slightly
crowded. Thin the annuals to stand anywhere from 6 to 12
inches apart, depending on the species or cultivar. Space
perennials 2 to 3 feet apart.
Sow seeds indoors about one month before you want to plant the
seedlings outdoors—which you can do as soon as the ground
can be worked—or before the average last spring frost in
your area. Some annual bachelor’s-buttons, such as the
Florence series, are day-length sensitive: They need at least
14 hours of daylight to set flower buds, so you may want to
supplement natural light with fluorescent or grow lights for
earliest bloom. The National Garden Bureau suggests the
- Fill individual peat pots, seed-starting flats, or
3-inch-diameter containers with a commercial seed-starting
mix. Moisten the mix and let it drain.
- Sow the seeds in rows in the flats. Sow 3 to 4 seeds per pot
and cover the seeds with a 1/2” layer of the mix because
centaureas need darkness to germinate. Spritz the mix with
water to moisten.
- Cover the containers with clear plastic to keep the mix
moist while the seeds are germinating and place in a warm
location (60-70 degrees).
- When the seedlings emerge, remove the plastic covers and put
the pots in a sunny location or under grow-lights. Water as
needed to keep the mix moist (not soggy).
- When seedlings are about 2 inches tall and have at least one
pair of true leaves, snip off all but the strongest plant in
each pot at soil level. (The first set of leaves is cotyledon
leaves—they usually do not resemble the true leaf shapes of
- Fertilize the seedlings once while they are growing indoors
with a water-soluble fertilizer.
- Centaureas grow best if you transplant them to the garden
before they are taller than four inches.
Selecting Plants at the Garden Center
In addition to growing centaureas from seed, you can purchase
potted plants at a local garden center or nursery. You may be
able to find small, young, green plants as well as those in
flower. Because of their compact habit, dwarf centaureas, like
the Florence and Midget series, may be more readily available
Look for plants with a lot of buds and only a few, if any,
open blossoms. Avoid leggy plants and those that are single
stemmed; you want to start out with compact, well-branched
plants, especially because of the centaurea’s habit of
becoming leggy as the season progresses. The leaves should not
be wilted, even though they are likely to recover when you get
them home and plant them. Be very watchful for signs of
disease, such as powdery mildew and rust. Some garden centers
sell pots or flats of mixed colors, but many offer packs of
blue bachelor’s-buttons, simply because it is the most
If you cannot put the plants in the garden right away, water
them well and set the pots out of direct sun until you can do
Plant centaureas in full or partial sun in any average,
slightly alkaline soil. Although they are not too particular
about fertility, you may want to dig some compost or dried
manure into the soil before planting—a 1- to 2-inch layer
should do. In hot zones, such as 8 to 10 and desert areas,
bachelor-buttons will grow better with some shade from the
- Transplant on a calm, cloudy day, so the plants can begin to
get acclimated before having to contend with sun and wind.
- Space the annuals about 12 inches apart. Give the perennials
room to spread—space them at least 2 feet apart.
- Taller varieties (including mountain bluet) may need
support, because the stems have a tendency to become floppy as
they grow. Stake or cage them when you transplant.
- Water the plants well immediately after planting.
Out in the Garden
All centaureas look good as part of an informal or wildflower
garden. They are especially attractive interplanted with red
poppies and snapdragons, or mixed with daylilies in a border.
They also belong in cutting gardens in mixed color
combinations or in blocks of individual colors. The foliage
may become rather ragged and unbecoming as the season
progresses—especially if the season has been rainy or very
hot—so set plants in borders or beds where the leaves and
flowers of other annuals and perennials will camouflage them.
- Many bachelor’s-buttons branch naturally, but you can
pinch the growing tips to encourage more branching, bushier
growth, and more flowers. C. americana does need to be
pinched, or you may end up with single-stalked plants.
Pinching perennial cornflower will also give you more flowers,
but it isn’t required. For slightly larger flowers, you can
remove the buds from young plants, but part of the charm of
cornflowers is their small, thistle like blooms.
- Perennial cornflower spreads very quickly by means of
underground stolons to cover any good, unplanted soil. To
control it in a garden bed, dig up and divide the plants every
two years. It prefers cool climates and does not grow well in
areas with hot, humid summers.
- Fertilize the plants monthly with a balanced fertilizer or
use a slow-release plant food at transplanting time.
- Water infrequently; centaureas are drought tolerant, and the
stems actually get rather floppy if the soil is too moist.
- Remove spent flowers to keep the plants producing new
- Centaureas will self-seed, but not reliably and not for more
than a year or two. It is best to start annuals with fresh
seed every year.
Centaureas are excellent flowers for cutting, whether you want
to use them fresh or dried. Freshly cut blooms last 4 to 5
days. The dried flowers retain their colors: Use the petals to
add bright hues to potpourri, or use the whole flowers in
For fresh arrangements, most gardeners grow the standard or
taller cornflowers, but dwarf bachelor’s-buttons also have
their uses. Cut the blooms in early morning when they are half
open and strip the lower leaves from the stems.
Bachelor’s-buttons combine beautifully with snapdragons,
sweet william, love-in-a-mist (Nigella), lavender, and the
blue spikes of Salvia farinacea (‘Victoria’) and red
spikes of Salvia splendens. The plants’ grayish foliage
harmonizes with the silvery leaves of artemisia and dusty
miller. Centaureas provide an informal, airy look with
floribunda and shrub roses. Use them in nosegays and swags as
well as in vase arrangements. Try wiring small bunches of the
blooms to napkin rings for a special occasion; the dwarf
Florence series works well in that design. The smaller flowers
are also delightful in miniature arrangements. And, of course,
go for tradition: Deck out a buttonhole with the
flowers—three to five stems backed by a bit of fern.
To dry whole blooms, pick them after the sun has evaporated
the dew—in late morning or in the afternoon. Select flowers
that have just opened or they will drop their petals when dry.
You can air-dry the flowers by tying 6 to 7 stems together in
bunches and hanging them upside down in an airy, dark place
for 2 to 3 weeks. You can also dry them in a desiccant, such
as silica gel: In a container with a lid, cover the flowers,
with 1-inch stems attached, completely with silica gel; close
the lid; the blooms should be dry in about 5 days. Dried
cornflowers combine well with such dried flowers as
strawflowers, everlastings, roses, zinnias, and lavender.
Centaureas in Containers
Because centaureas are quite drought resistant, they do very
well in containers, where the soil can dry out quickly. Plant
them in window boxes or standard containers in combination
with other annuals, such as geraniums, zinnias (Z.
angustifolia in particular), lobelia, fan flower (Scaevola),
and dusty miller. Dwarf varieties, such as the Florence
series, are the most adaptable to window boxes.
- Make sure the container has drainage holes in the bottom or
sides. Use a lightweight, soilless mix, not garden soil.
Garden soil may contain weed seeds, and it is heavier than a
soilless mix—something to consider if you want to move the
containers around or if you are planting a window box on a
sill or railing on a deck or balcony.
- If you want to avoid the chore of fertilizing the plants
during the season, incorporate a controlled-release fertilizer
in the mix before planting.
- Position cornflowers among the other plants in a random
placement; their sometimes-lax stems will weave through the
other flowers for a delightfully informal look. Set dwarf
cornflowers toward the front edge of the container.
- To plant, unpot plants and place them in the mix at the same
level they were growing originally. Water the planting well.
- Check the soil in the pots daily in very hot weather and
water as needed to keep it barely evenly moist.
- Fertilize monthly with a water-soluble plant food, if you
didn’t use a slow-release fertilizer at planting time.
Diseases and Pests
About the only pest that may bother cornflowers is the aphid.
Aphids are easy to deter simply by washing the plants off with
a strong spray of water from a garden hose.
In wet weather, two fungal diseases may be a problem: rust and
powdery mildew. You can help prevent powdery mildew by spacing
the plants so there is good air circulation. Watering from
below, so you don’t wet the leaves, helps as well, but
there’s not too much you can do to protect them from
nature’s rain. Remove infected leaves as soon as you see
To control rust, spray with a fungicidal soap or sulfur.
Remove affected leaves and stems (don’t compost them). Use
drip irrigation instead of a hose to water the plants.
Special thanks to
Eleanore Lewis as the author of this article. Thanks also go
to the two experts who reviewed the text for accuracy before
publishing. Thanks to Dennis Kromer of Wild West Seed Inc.,
and Albert Stuurman of PanAmerican Seed Company for checking
the text for publication.