Flowers by colour

Blue flowers, and which ones are really blue

True blue is the rarest colour in the garden, and most flowers sold as blue are violet in good light. Here is the honest sort: what reads blue in a bed, what leans violet, and what is blue only on the label.

Gentian Delphinium Cornflower Iris Forget-me-not Blue flax Catmint Balloon flower
The flowers

Every blue flower in the library

29 of the 82 flowers here carry this colour, ordered by how much of it the photograph actually shows. The library keeps one picture per flower and most of these come in several colours.

LupineBlue-violet LupineLupinus polyphyllus (and Russell hybrids, Lupinus × hybridus)Spring bloomer
Russian SageBlue-violet Russian SageSalvia yangii (syn. Perovskia atriplicifolia)Summer bloomer
Bigleaf HydrangeaIt depends on your soil Bigleaf HydrangeaHydrangea macrophyllaSummer bloomer
8 photos of Bigleaf Hydrangea
Blue hydrangea Blue hydrangea Bigleaf Hydrangea Blue hydrangea Flower Bigleaf Hydrangea Blue hydrangea Bigleaf Hydrangea Blue hydrangea
African Lily (Lily of the Nile)Sold as blue African Lily (Lily of the Nile)Agapanthus praecoxSummer bloomer
LavenderSold as blue LavenderLavandula angustifoliaSummer bloomer
Globe ThistleBlue-violet Globe ThistleEchinops ritroSummer bloomer
8 photos of Globe Thistle
Blue globe thistle Globe Thistle Blue globe thistle Globe Thistle Blue globe thistle Blue globe thistle Globe Thistle Globe Thistle
Blue Salvia (Mealycup Sage)Blue-violet Blue Salvia (Mealycup Sage)Salvia farinaceaSpring bloomer
8 photos of Blue Salvia (Mealycup Sage)
Blue mealycup sage flower Blue Salvia (Mealycup Sage) Blue mealycup sage flower Blue mealycup sage flower Blue mealycup sage flower Blue mealycup sage flower Blue Salvia (Mealycup Sage) Blue mealycup sage flower
Forget-Me-NotTrue blue Forget-Me-NotMyosotis sylvaticaSpring bloomer
8 photos of Forget-Me-Not
Blue forget-me-nots flowers Forget-Me-Not Blue forget-me-nots flowers Delicate blue flowers with yellow centers Blue forget-me-nots flowers Blue forget-me-nots flowers Blue forget-me-nots flowers Blue forget-me-nots flowers
CatmintBlue-violet CatmintNepeta x faasseniiSpring bloomer
Blue FlaxTrue blue Blue FlaxLinum perenneSpring bloomer
8 photos of Blue Flax
Blue Flax Blue Flax Blue flax Linum Flower Blue flax Linum Flower Blue flax Linum Flower Blue flax Linum Flower Blue flax Linum Flower Blue flax Linum Flower
Cornflower (Bachelor's Button)True blue Cornflower (Bachelor's Button)Centaurea cyanusSpring bloomer
8 photos of Cornflower (Bachelor's Button)
Cornflower (Bachelor's Button) Blue cornflower flower Cornflower (Bachelor's Button) Blue cornflower flower Blue cornflower flower Blue cornflower flower Blue cornflower flower Blue cornflower flower
IrisBlue-violet IrisIrisSpring bloomer
Candle larkspurTrue blue Candle larkspurDelphinium elatumSummer bloomer
8 photos of Candle larkspur
Blue delphinium Candle larkspur Blue delphinium Blue delphinium Blue delphinium Blue delphinium Candle larkspur Candle larkspur
Bird of ParadiseSold as blue Bird of ParadiseStrelitzia reginaeCool-season bloomer
BellflowerBlue-violet BellflowerCampanula persicifoliaSummer bloomer
8 photos of Bellflower
Blue bellflower Bellflower Bellflower Bellflower Blue bellflower Blue bellflower Blue bellflower Blue bellflower
BellflowerBlue-violet BellflowerCampanula spp.Spring bloomer
8 photos of Bellflower
Blue bellflower Bellflower Bellflower Bellflower Blue bellflower Blue bellflower Blue bellflower Blue bellflower
GentianTrue blue GentianGentiana acaulis (Stemless/Trumpet Gentian); genus GentianaSpring bloomer
8 photos of Gentian
Blue gentian flower Gentian Blue gentian flower Gentian Blue gentian flower Blue gentian flower Blue gentian flower Gentian
Love-in-a-MistBlue-violet Love-in-a-MistNigella damascenaSpring bloomer
8 photos of Love-in-a-Mist
Love-in-a-Mist Love-in-a-Mist Love-in-a-Mist Love-in-a-Mist Blue Virginia bluebells Blue Virginia bluebells Blue Virginia bluebells Blue Virginia bluebells
Great Blue LobeliaTrue blue Great Blue LobeliaLobelia siphiliticaSummer bloomer
8 photos of Great Blue Lobelia
Great Blue Lobelia Great Blue Lobelia Flower Great Blue Lobelia Flower Great Blue Lobelia Flower Great Blue Lobelia Flower Great Blue Lobelia Great Blue Lobelia Flower Great Blue Lobelia
Virginia BluebellsTrue blue Virginia BluebellsMertensia virginicaSpring bloomer
8 photos of Virginia Bluebells
Virginia Bluebells Virginia Bluebells Blue Virginia bluebells Blue Virginia bluebells Virginia Bluebells Blue Virginia bluebells Blue Virginia bluebells Virginia Bluebells
Morning GloryTrue blue Morning GloryIpomoea purpurea / Ipomoea tricolorSummer bloomer
8 photos of Morning Glory
Blue morning glory flower Morning Glory Blue morning glory flower Morning Glory Blue morning glory flower Blue morning glory flower Blue morning glory flower Blue morning glory flower
Balloon FlowerTrue blue Balloon FlowerPlatycodon grandiflorusSummer bloomer
Garden PhloxSold as blue Garden PhloxPhlox paniculataSummer bloomer
ClematisSold as blue ClematisClematisSpring bloomer
AsterBlue-violet AsterAster amellusSummer bloomer
AnemoneSold as blue AnemoneAnemone coronariaSpring bloomer
PetuniaSold as blue PetuniaPetunia x hybridaSpring bloomer
Bearded IrisBlue-violet Bearded IrisIris germanicaSpring bloomer
8 photos of Bearded Iris
Blue bearded iris flower Bearded Iris Bearded Iris Blue bearded iris flower Bearded Iris Blue bearded iris flower Bearded Iris Blue bearded iris flower
Garden VerbenaSold as blue Garden VerbenaVerbena x hybridaSpring bloomer
Blue pincushion flower Pincushion FlowerScabiosa caucasica
7 photos of Pincushion Flower
Pincushion Flower Pincushion Flower Blue pincushion flower Blue pincushion flower Blue pincushion flower Pincushion Flower Pincushion Flower
Blue agapanthus flower AgapanthusAgapanthus
7 photos of Agapanthus
Agapanthus Blue agapanthus flower Blue agapanthus flower Blue agapanthus flower Blue agapanthus flower Agapanthus Agapanthus
Why

Why blue is the colour it is

Blue is rare because a plant cannot simply make a blue pigment. It builds blue out of the same delphinidin pigments that make red and purple, then bends the colour with cell pH, metal ions and pigment stacking. Get one of those wrong and the flower comes out mauve. Hydrangea is the visible proof: the same shrub runs pink in limey soil and blue in acid soil, because aluminium only becomes available to the plant when the soil is sour.

If you want the blue

If you want hydrangea blue, the target is soil pH around 5.2 to 5.5 with aluminium available. Above pH 6.5 the same plant will be pink whatever the label promised.

The honest sort

How blue each one really is

The same flowers again, this time grouped by how much of the colour is actually there in ordinary daylight rather than on a label.

True blue9Reads blue at three paces, in ordinary daylight.
Blue gentian flowerGentian Cornflower (Bachelor's Button)Cornflower (Bachelor's Button) Blue forget-me-nots flowersForget-Me-Not Blue FlaxBlue Flax Blue delphiniumCandle larkspur Great Blue LobeliaGreat Blue Lobelia Virginia BluebellsVirginia Bluebells Blue morning glory flowerMorning Glory
Also here Balloon Flower
Blue-violet10Blue in the shade, violet in full sun. Both readings are fair.
Blue bearded iris flowerBearded Iris IrisIris Blue mealycup sage flowerBlue Salvia (Mealycup Sage) CatmintCatmint Russian SageRussian Sage Blue globe thistleGlobe Thistle Love-in-a-MistLove-in-a-Mist Blue bellflowerBellflower LupineLupine
Also here Aster
Sold as blue8Violet, mauve or purple. Lovely, but not blue.
LavenderLavender African Lily (Lily of the Nile)African Lily (Lily of the Nile) Bird of ParadiseBird of Paradise
Also here Clematis Petunia Garden Verbena Anemone Garden Phlox
It depends on your soil1The same plant, two colours, decided underground.
Blue hydrangeaBigleaf Hydrangea
Putting it together

What blue sits well with

Blue and lemon yellowThe strongest contrast in the garden; blue reads deeper next to it.
Blue and whiteCools everything down and doubles the apparent light in shade.
Blue and apricotWarmer and less obvious than blue with pink.
Meaning

What blue says

Blue carries calm, trust and distance: the colour of the thing just out of reach. Forget-me-not is the exception that is entirely about staying near.