How-to Guide
How to Grow Cardinal Flower
The short answer
Grow cardinal flower (Lobelia cardinalis) in rich, constantly moist to wet soil in full sun to part shade — it needs constant moisture, tolerates brief flooding, and should never be allowed to dry out. It reaches two to four feet, blooms scarlet from July to September, and is a favorite of hummingbirds and butterflies. It is hardy roughly zones 3–9.
It is a somewhat short-lived perennial that persists by self-seeding and by overwintering as a basal rosette of leaves at the crown. Protect that rosette: in cold-winter areas mulch the roots to prevent frost heaving, but keep mulch off the crown itself, and don't let winter wet-then-dry cycles kill it.
Moisture is non-negotiable
Cardinal flower grows wild along streams, springs, swamps, and low wooded areas, and the garden plant keeps that thirst. It needs constant moisture, tolerates brief flooding, and its soil should never be allowed to dry out — drought is the fastest way to lose it.
Grow it in rich, medium-to-wet soil in full sun to part shade; in warmer regions it appreciates some afternoon shade, while in cooler climates it takes more sun. It is an ideal plant for rain gardens, pond edges, and the low, wet spots where many perennials struggle.
Reaching two to four feet, it sends up erect spikes of large, cardinal-red flowers from July to September, and is hardy in zones 3–9. A layer of mulch helps hold the soil moisture it demands.
Hummingbird magnet
The tubular scarlet flowers are very attractive to butterflies and hummingbirds — the red, nectar-rich spikes are practically designed for hummingbird bills, and a stand in bloom draws them reliably. (Despite the name, it does not attract cardinals the birds.)
Its late-summer bloom fills an important nectar gap, so it earns a place in any hummingbird or pollinator planting sited somewhere reliably moist.
Short-lived — protect the overwintering rosette
Cardinal flower is a somewhat short-lived perennial. It carries on in two ways: it self-seeds, and each plant overwinters as a basal rosette of leaves that must survive to regrow the following year.
That rosette is the vulnerable part. In cold-winter climates, apply mulch over the roots to protect the root system and prevent frost heaving that would lift the crown out of the ground — but keep heavy, wet mulch off the rosette itself so it doesn't smother or rot.
Let some flower spikes go to seed to keep a supply of replacement seedlings coming, since individual plants fade after a few years. Between self-sowing and a protected rosette, a colony can persist indefinitely even as individuals turn over.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Missouri Botanical Garden Plant Finder — Lobelia cardinalis — A somewhat short-lived, clump-forming perennial reaching 2–4 feet; needs constant moisture, tolerates brief flooding, and soils should never be allowed to dry out; grows in medium to wet soils in full sun to part shade; scarlet flowers bloom July to September and are very attractive to butterflies and hummingbirds; recommended for rain gardens and moist areas; in cold winter climates apply root mulch to protect the roots and prevent root heaving; hardy zones 3–9.