Blue flowers hold a distinct allure in gardens and natural landscapes. Their cool, calming tones introduce a unique depth, making them a sought-after color in horticulture. While true blue can be elusive, blue-hued blossoms offer a wide array of choices for those seeking to incorporate this captivating color.
Common Blue Flower Varieties
Many flowering plants offer blue varieties.
Delphiniums, known for their tall spires, produce intense blue flowers that stand out in perennial borders. These blooms often feature multiple florets clustered along a central stem, creating a dramatic vertical accent.
Hydrangeas, particularly Hydrangea macrophylla varieties, are known for their large, spherical flowerheads that can display shades of blue, pink, or purple. The blue coloration in hydrangeas is influenced by soil conditions, allowing gardeners to adjust their plant’s hue.
Forget-Me-Nots (Myosotis) are low-growing annuals or short-lived perennials that produce tiny, sky-blue flowers with yellow centers. They often create a carpet-like effect in spring gardens and are known for their ability to self-seed.
Bluebells (Hyacinthoides non-scripta) are woodland perennials with drooping, bell-shaped, violet-blue flowers. These blooms appear in spring, often forming a blue carpet beneath trees.
Gentians are known for their vibrant, trumpet-shaped blue flowers, often blooming in late summer to fall. Many species are known for their saturated blue hues, with Gentiana acaulis noted for its color.
Cornflowers (Centaurea cyanus), also called bachelor’s buttons, are annuals that produce blue, thistle-like flowers. They bloom from early summer until the first fall frost, popular for meadows and informal gardens.
Salvia, a diverse genus, includes many varieties with blue flowers, such as Salvia patens and Salvia ‘May Night’. These plants often feature spikes of blue blooms that attract pollinators.
Lobelia species, such as Lobelia siphilitica (Great Blue Lobelia), display blue or purplish-blue flowers. Many lobelias have a two-lipped tubular flower structure with five lobes.
Irises are common in blue, with many varieties having blue-violet petals and unique flower structures. The Blue Flag Iris (Iris versicolor) is a North American native with blue-violet flowers and sword-like leaves.
The Chemistry Behind Blue Blooms
The blue color in flower petals stems from a group of pigments called anthocyanins, which are water-soluble molecules found within plant cells. Anthocyanins are responsible for a wide range of colors in plants, including reds, purples, and blues, depending on their chemical structure and cellular environment. Delphinidin is a type of anthocyanin associated with blue coloration in flowers.
However, the presence of delphinidin alone does not guarantee a blue hue. The final color is influenced by the pH level within the plant cells, particularly in the vacuoles where anthocyanins are stored. A more alkaline (higher pH) environment tends to promote blue shades, while acidic (lower pH) conditions can shift the color towards red or pink. For instance, the blue pigment of the cornflower, protocyanin, is a complex involving anthocyanins, flavone glycosides, and metal ions like iron, magnesium, and calcium.
Co-pigmentation plays a role, where colorless or slightly yellow co-pigments, often other flavonoids, interact with anthocyanins to stabilize and deepen the blue color. This interaction shifts the light absorption spectrum of the anthocyanin, causing a “bluing effect.” Additionally, metal ions such as aluminum, iron, and magnesium can complex with anthocyanins, forming metalloanthocyanins that contribute to blue coloration, as seen in the blue hydrangea where aluminum ions are involved.
Bringing Blue Flowers to Your Garden
Incorporating blue flowers into a garden design can create a visually appealing space. Blue blooms can serve as accents, providing a contrast to other colors in the landscape. Pairing blue with its complementary color, orange, can create a vibrant display. Alternatively, combining blue flowers with analogous colors like purple can result in a harmonious look.
For certain plants, such as hydrangeas, environmental factors influence the blue color. The blue hue of Hydrangea macrophylla is linked to the availability of aluminum ions in the soil, affected by soil pH. Acidic soil, with a pH below 6, allows hydrangeas to absorb aluminum more readily, leading to blue flowers. Conversely, in alkaline soil (pH above 7), aluminum becomes less available, and the flowers are pink.
Gardeners can manipulate soil pH to encourage blue hydrangea blooms by adding sulfur or aluminum sulfate to lower the pH. However, it is important to make gradual adjustments to avoid stressing the plant and to monitor soil pH regularly. While achieving a pure blue can be challenging due to the complex chemistry involved, many plants offer blue-like shades that enhance gardens. Blue flowers thrive in full sun, but some varieties like bluebells and certain salvias tolerate partial shade.