Blue Perennial Flower Identification by Flower Shape

To identify a blue perennial flower, sort the bloom by shape first — a spike of many small flowers, a bell, a flat five-petalled star, or a pea-like flower — then check the stem (square or round), the leaves and the month it is blooming. Those four checks narrow a garden's worth of blue flowers to two or three candidates.

The three pages that rank for this search are plant lists: Walters Gardens shows 17 blue perennial cultivars, Epic Gardening profiles 21 plants and ProFlowers lists 41 blue flowers including annuals and bulbs. None of them sorts the plants by what you can see. This page does, using plant records from NC State Extension's Plant Toolbox for leaf, stem and toxicity details.

• Spike of small flowers: salvia, catmint, Russian sage, speedwell (Veronica), delphinium, lupine, great blue lobelia.
• Bell or balloon: balloon flower, bellflower (Campanula), Virginia bluebells, bush clematis.
• Flat five-petalled star: eastern bluestar (Amsonia), Siberian bugloss (Brunnera), forget-me-not, lungwort.
• Pea-shaped or hooded: blue false indigo (Baptisia), monkshood (Aconitum).
• Big rounded head of trumpets: agapanthus (lily of the Nile).

Spikes are the largest group, so the stem and leaves do most of the work here:

• Woodland sage (Salvia nemorosa): small violet-blue to lavender flowers in whorls on spikes, June to September; square stems; wrinkled, toothed leaves 3 to 4 inches long that smell when crushed; 1.5 to 3 feet tall; zones 4a to 8b (NC State Extension). Walters Gardens lists the cultivar 'Crystal Blue' as light sky blue.
• Catmint (Nepeta x faassenii): 0.5-inch two-lipped violet-blue flowers; square green stems; 1 to 2 inch gray-green oval leaves with rounded teeth, aromatic when crushed; 18 to 24 inches tall; zones 5a to 9b. NC State notes it is sterile and does not reseed like common mint.
• Russian sage (Salvia yangii, formerly Perovskia atriplicifolia): pale blue to deep purple flowers June through October; grayish-silver, deeply cut aromatic leaves; stiff, square, silvery stems that stand through winter; 2 to 4 feet; zones 5a to 9b (NC State Extension).
• Speedwell (Veronica): Walters Gardens describes 'Blue Skywalker' as tall with lavender-blue spikes in mid to late summer, zones 4 to 8.
• Delphinium: tall spikes in blue, purple, pink or white, May to midsummer (NC State Extension); Epic Gardening gives up to 6 feet tall. Poison severity high — see the safety section below.
• Lupine: spikes up to 4 feet with a long bloom period in spring and summer (Epic Gardening).
• Great blue lobelia (Lobelia siphilitica): light to dark blue tubular two-lipped flowers with striped tubes, July to October, in wet to moist soil; native to eastern North America; 1.5 to 4 feet (NC State Extension).

Square stem plus a scent when you rub a leaf points to the mint family (salvia, catmint, Russian sage). A round stem with no scent points to speedwell, delphinium or lupine.

• Balloon flower (Platycodon grandiflorus): the unopened buds swell like hot-air balloons, then open into blue or white bells with five pointed lobes; the genus name means 'flat bell'. Late spring to summer, 1 to 2 feet, zones 3a to 8b (NC State Extension).
• Clustered bellflower (Campanula glomerata): Walters Gardens describes 'Church Bells' as violet-purple bells in tight clusters, late spring to midsummer, zones 5 to 8.
• Virginia bluebells (Mertensia virginica): pink buds turn into nodding, slightly fragrant blue bells 3/4 to 1 inch long from March to May for about three weeks; smooth, oval, bluish-green leaves; the whole plant dies back in midsummer and returns the next spring. Native to eastern North America, zones 3a to 9b (NC State Extension).
• Bush clematis: Walters Gardens describes 'Stand By Me' as blue bell-shaped flowers on a non-climbing plant that needs staking, zones 3 to 7.

If the blue bells hang downward in early spring and the plant has vanished by July, it is almost certainly Virginia bluebells, not a planting that died.

• Eastern bluestar (Amsonia tabernaemontana): light blue star-like flowers about 3/4 inch across with 4 to 5 petals, April into early summer; narrow willow-like leaves that turn golden-yellow in fall; a toxic white latex in the foliage; 2 to 3 feet; zones 3a to 9b; native to central and eastern North America (NC State Extension). Break a leaf: milky sap confirms it.
• Siberian bugloss (Brunnera macrophylla): small blue five-petalled flowers with white centers that look like forget-me-nots, spring to early summer, over dark green heart-shaped leaves up to 6 inches wide; part to deep shade; zones 3a to 8b (NC State Extension).
• Forget-me-not (Myosotis): Epic Gardening describes five-petalled blue flowers with yellow centers in spring. Tiny flowers over small leaves means forget-me-not; the same flower over big heart-shaped leaves means Brunnera.
• Lungwort (Pulmonaria): Walters Gardens describes 'Twinkle Toes' as light periwinkle blue flowers over dark green leaves sprinkled with silver, part to full shade, zones 3 to 9; Epic Gardening gives 6 to 12 inches tall with flowers at winter's end.

• Blue false indigo (Baptisia australis): bright indigo pea-shaped flowers about 0.75 inch on spikes up to 16 inches, late spring; clover-like leaves in threes, blue-green; puffy seed pods up to 2.5 inches that ripen black by late summer; 3 to 4 feet; zones 3a to 9b; native to the central and eastern US. Poison severity low: all parts can cause nausea, vomiting and diarrhea if eaten in quantity (NC State Extension).
• Monkshood (Aconitum): blue, purple or white flowers in spikes up to 8 inches long, each with a hood or helmet on top; summer; 3 to 4 feet; zones 3a to 7b. Poison severity high; every part is toxic (NC State Extension).

A hood on top of each flower is the single most important thing to notice in a blue border, because it separates monkshood from the harmless-looking spikes around it.

Several popular blue perennials are poisonous. NC State Extension rates them as follows:

• Monkshood (Aconitum): high. Toxic alkaloids including aconitine in every part; symptoms listed include burning and numbness of the mouth, vomiting, weak pulse and convulsions; poisonous to people and pets. NC State advises gloves when handling.
• Delphinium: high. Flowers, leaves, seeds and stems contain alkaloids; NC State says it can cause serious illness or death and lists cats, dogs and horses as affected.
• Great blue lobelia: low. All parts contain alkaloids that can cause nausea, vomiting and neurological symptoms if eaten.
• Blue false indigo: low. All parts poisonous if eaten in quantity; no contact dermatitis.
• Eastern bluestar: a toxic white latex in the foliage.

Wear gloves when cutting monkshood or delphinium, keep children and pets away from the plants, and do not use any of them for food or tea. If someone may have eaten part of one, contact poison control or a doctor right away, and call a vet for a pet. An app match or a web page is not a reason to assume a plant is harmless.

Catalog names give it away: periwinkle blue, lavender-blue, violet-blue, indigo. True sky blue is uncommon because the pigment behind it does not produce blue on its own. Wikipedia's article on blue flower colouration explains that blue petals are caused by delphinidin, a type of anthocyanin, but that delphinidin needs an alkaline cell environment, a complex with flavones and metal ions, or another mechanism to turn blue.

Two examples from the same article show why a plant's blue can change:

• Morning glory: the cell sap pH rises from 6.6 in the bud to 7.7 in the open flower, shifting the color from purple to blue.
• Hydrangea: blue flowers carry more aluminum ions and a higher cell pH (about 4.1 versus 3.3 in red flowers). Epic Gardening and ProFlowers both note that soil acidity changes hydrangea color.

For identification this matters: do not rule a plant out because its flowers look more purple than the photo you are comparing against. Shape, stem and leaves are more reliable than exact shade.

These perennials return each year within the hardiness zones their sources give (USDA zones; check yours before planting):

• Spring: lungwort, Virginia bluebells (zones 3a to 9b), Siberian bugloss (3a to 8b), eastern bluestar (3a to 9b), blue false indigo (3a to 9b) — NC State Extension, except lungwort (Walters Gardens, zones 3 to 9).
• Early summer: Siberian iris 'Cape Cod Boys', periwinkle blue with dark veins (Walters Gardens, zones 3 to 9); delphinium; catmint (5a to 9b).
• Mid to late summer: woodland sage (4a to 8b), balloon flower (3a to 8b), monkshood (3a to 7b), agapanthus 'Little Galaxy' midsummer to early fall — Walters Gardens says it is hardy to zone 6 and has come through seven of its own snowy winters.
• Late summer into fall: Russian sage June to October (5a to 9b), great blue lobelia July to October (4a to 9b), azure aster (Symphyotrichum oolentangiense) in fall, zones 3 to 9 (Epic Gardening).

Some plants on the ranking lists are not what they seem: ProFlowers lists cornflower — which its own text calls an annual — alongside love-in-a-mist and sweet pea, two more plants usually grown as annuals rather than perennials, and Walters Gardens includes blue fescue and a blue hosta, whose blue is in the leaves rather than the flowers.

The same common name can point to different plants, so check the scientific name before you buy or compare photos:

• Periwinkle: Epic Gardening's 'periwinkle' is Catharanthus roseus, while ProFlowers lists Corydalis flexuosa under the same name.
• Delphinium: ProFlowers lists mountain larkspur (Delphinium scaposum) and garden delphinium separately; both belong to the genus NC State rates high for poison.
• Russian sage: now filed as Salvia yangii rather than Perovskia atriplicifolia (NC State Extension), so older labels and newer records use different names for the same plant.

NatureLens identifies a flower from a photo, with free scans every day. Take three pictures for the best result:

• the flower face-on, filling most of the frame;
• the whole spike or stem from the side, so the arrangement shows;
• one leaf, top side, with a finger or coin for size.

Then use the checks on this page to confirm the answer: square stem and scent, milky sap, leaves in threes, a hood on the flower. For more general tips, see how to identify a plant.

Research and drafting for this page used AI assistance. Every measurement, date and claim was then checked against the sources listed below, which were opened and read on 2026-09-25. Where two sources give different numbers, both are shown with the source named.