Add some blues to your garden

Cornflowers have been grown in gardens in North America since colonial times, primarily from seeds brought over from Europe.
Today 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 or basket flower; and C. montana, mountain bluet, or perennial cornflower.
The different common names have originated from the early history of the flower. Cornflowers are appropriately named as they grow wild in corn fields in Europe and North America, 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. And 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 shallow basket).
Best of all, this family of flowers is known for its shades of blue flowers. Not many species of plants offer true-blue flowers, but the Centaurea family certainly has many shades of true blue to choose from.
A confusing aspect of this family of flowers is that they contain both annual and perennial species. Annual bachelor’s-buttons (C. americana) and basket flowers begin to bloom in late spring and continue throughout the summer.
This species is an annual native to the south-central and southeastern United States, but can grow throughout Canada, as well. This species is commonly mistaken as a perennial because it commonly self-seeds and then grows again next year.
When an annual plant self-seeds, the seeds form a new plant the next growing season. Because the new plant often is in the same spot as where the annuals were planted the previous summer, it appears to be a perennial but is really a new annual flower sprouting up.
The common perennial species from this family is known as the mountain bluet, or perennial cornflower. These flowers are native to the mountains of Europe, and bloom from late spring to early summer.
It is hardy to Zone 3 and produces fringed, violet-blue flowers with deep purple centres.
You also might recognize another well-known member of the Centaurea genus, the bedding plant dusty miller, C. cineraria.
This plant is really a perennial in Zones 9-5 (outside of our area) and is grown for its greyish foliage, but most gardeners don’t realize this plant produces purple flowers because we treat it as decorative foliage plant and an annual in our area.
The flowers are rather unattractive, but we all know the leaves make up for the lack of beauty in the flowers.
Centaureas produce single- and double-fringed blooms on plants that range in height from 10 inches to 2.5 feet, depending on the species or cultivar (basket flowers can reach four feet in height).
The shape of the flower petals resembles that of thistles, but the plants’ leaves do not have spines like thistles. The leaves often are an attractive gray-green.
Mountain bluet grows about two feet tall with an equal spread. The flowers usually are lavender blue, but you also may find plants with rose, pale yellow, or white blooms.
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.
Colours include violet, red, pink, lavender, blue, and white.
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 centres so they can be started from seed.
Perennial mountain bluet simply takes a little longer to germinate than the annual kinds. But started early enough, it may bloom the first year it is planted.
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 likely are to recover when you get them home and plant them. Also be very watchful for signs of disease, such as powdery mildew and rust.
Plant Centaureas in full or partial sun. Although they are not too particular about fertility, you may want to dig some compost or dried manure into the soil before planting (a one- to two-inch layer should do).
Transplant on a calm, cloudy day so the plants can begin to get acclimated before having to contend with sun and wind.
Space annual varieties about 12 inches apart but give perennials species room to spread—space them at least two 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.
Make sure to water the plants well immediately after planting. Fertilize the plants monthly with a balanced fertilizer or use a slow-release plant food at transplanting time.
Tips for longer lasting blooms:
•water infrequently as Centaureas are drought tolerant and the stems actually get rather floppy if the soil is too moist; and
•remove spent flowers to keep the plants producing new blooms.
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.
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.
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. Pinching perennial cornflower also will 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.
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.
About the only pest that may bother cornflowers is the aphid, which are easy to deter simply by washing the plants off with a strong spray of water from a garden hose.
In wet weather, fungal diseases such as rust and powdery mildew may be a problem. 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 them and throw them in the garbage—not the composter.
To control rust, spray with a fungicidal soap or sulphur. Remove affected leaves and stems (don’t compost them), and use drip irrigation instead of a hose to water the plants.
As you can see, this family of plants has a lot of beauty to offer to your garden, whether you are just interested in some dusty miller for the borders of your beds or some blue flowers for contrast, or something a little different in texture and colour.
As an added bonus, Centaureas are excellent flowers for cutting, whether you want to use them fresh or dried. Freshly-cut blooms last four-five days.
And the dried flowers retain their colours so you can use the petals to add bright hues to potpourri, or use the whole flowers in arrangements.
So add some blues to your garden—I’m sure you’ll be happy you did.

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