Blood flower (Asclepias curassavica) gets its name from the vivid orange-red blossoms that cover it from early summer until frost. Gardeners also know it as tropical milkweed, Mexican butterfly weed, or scarlet milkweed, a member of the same genus as the milkweeds native to North America. In warm climates it grows as a tender perennial; in colder zones, gardeners raise it as an annual that delivers months of color in a single season. The flowers draw monarch butterflies, bees, and hummingbirds, and the plant asks for little beyond full sun and well-drained soil. Gardeners who already grow flowering perennials will recognize the routine: the basics of lupine plant care for growing bluebonnets and perennial flower spikes, namely full sun, sharp drainage, and regular deadheading, apply to blood flower as well.
Meet the Blood Flower: Names, Origins, and Growth Habits
A Milkweed With Many Common Names
Asclepias curassavica is native to tropical South America and Central America and has naturalized across warm parts of the United States and the Caribbean. The species name comes from Curaçao, where early botanists catalogued the plant. The blood flower name refers to the red-orange blooms, while tropical milkweed and scarlet milkweed describe its origin and flower color; Mexican butterfly weed hints at how strongly it attracts monarchs. Like other milkweeds, it belongs to the dogbane family (Apocynaceae) and produces a milky sap containing cardiac glycosides; the sap is bitter and toxic in quantity, and the same compounds concentrate in the leaves where monarch caterpillars feed.
Growth Habits and Hardiness
Blood flower grows 2 to 4 feet tall with an open, airy habit and narrow lance-shaped leaves. It blooms continuously from late spring through fall, and year-round in frost-free climates. It is hardy in USDA zones 8 through 11, where it survives winter outdoors and returns from the roots each spring. North of zone 8, most gardeners treat it as an annual, planting after the last frost. The plant self-seeds freely, so a single summer of bloom often produces volunteers the following year.
Hardiness Zones at a Glance
Zones 8 through 11 can leave plants in the ground all winter. Zones 6 and 7 can overwinter containers indoors, and zone 5 and colder gardens should treat blood flower as a summer annual.
Choosing Seeds and Plants
Blood flower grows easily from seed and is one of the quickest milkweeds to bloom in its first year, often within 10 to 12 weeks of sowing. The same care that goes into selecting high-quality seeds for home vegetable and flower gardens applies here: buy from a reputable source, check the harvest year, and store seed in a cool, dry place. Transplants at garden centers in spring give a head start of several weeks; inspect any plant for aphids and yellowing leaves before buying.
| Species | Native range | Height | Flower color | Soil preference |
|---|---|---|---|---|
| Blood flower (A. curassavica) | South and Central America | 2-4 ft | Orange-red | Well-drained |
| Common milkweed (A. syriaca) | Eastern North America | 3-5 ft | Pink-purple | Dry to medium |
| Butterfly weed (A. tuberosa) | Eastern and central U.S. | 1-2.5 ft | Orange | Dry, sandy |
| Swamp milkweed (A. incarnata) | Eastern North America | 3-5 ft | Pink | Moist |
The native species are the ones monarch researchers recommend for most gardens, for reasons covered later. Blood flower remains popular anyway because it blooms fast and shrugs off heat.
Planting Blood Flower in the Garden
Site Selection and Soil Preparation
Blood flower wants full sun, at least six hours of direct light a day, and soil that drains quickly after rain. It tolerates a wide pH range, but standing water rots the fleshy roots. In heavy clay, the drainage problems that make planting a flower bed in clay soil so tricky can kill milkweed within weeks; work several inches of compost into the bed before planting, or build a raised bed. On sandy soil, add organic matter to hold moisture; a south-facing bed against a wall warms early in spring and extends bloom late into fall.
Spacing and Planting Depth
Set transplants at the same depth they grew in the nursery pot and water in well. Space plants 12 to 18 inches apart so mature clumps fill in without crowding; dense planting invites mildew. In mixed beds, give taller species the back row. Drifts of three or more plants give monarchs a visible target from the air.
- Loosen the soil to a depth of 8 to 10 inches and mix in compost.
- Dig a hole slightly wider than the root ball.
- Set the plant at its original depth and backfill.
- Water deeply, then add a 2-inch layer of mulch, keeping it away from the stem.
Container Growing
Blood flower is one of the best milkweeds for pots because it stays compact and blooms nonstop. Choose a container at least 12 inches wide with drainage holes and a quality potting mix rather than garden soil. Container plants dry out faster than bed plants, so check them daily in summer heat and feed lightly every few weeks.
Choosing a Pot and Potting Mix
Plastic and glazed ceramic pots hold moisture longer than unglazed clay. Add a saucer for drainage and refresh the top inch of mix each spring; a patio pot also makes overwintering easy, since the whole plant can move indoors before frost.
Seasonal Care: Water, Fertilizer, and Pruning
Watering and Feeding
Once established, blood flower tolerates short dry spells, but consistent moisture produces more flowers. Water deeply about once a week when rain is scarce, more often for containers. Feed lightly: a low-nitrogen fertilizer every four to six weeks, or a spring compost topdressing, keeps plants blooming without pushing soft, aphid-prone growth. Heavy nitrogen feeding can change the chemistry of the leaves that monarch caterpillars eat, so err on the side of less.
Deadheading and Cutting Back
Deadheading spent flower clusters keeps the plant tidy and pushes out new buds; cut a finished stem back to a leaf node and it responds with a new flush of flowers. In frost-free regions, an annual hard cut in late winter, down to 6 to 8 inches, rejuvenates the plant and mimics the die-back that native milkweeds experience. Gardeners in Florida and Texas often cut back twice a year for the same reason.
Designing With Blood Flower
Blood flower pairs well with ornamental grasses, salvia, lantana, and zinnias. For layout guidance, flower bed ideas for home gardens cover layouts, plant pairings, and seasonal care, and most schemes translate directly to a monarch garden. Place the plant where you can watch it from a window, since the constant motion of visiting butterflies is half the show; its upright form adds height without bulk in mixed borders.
Overwintering and Propagation
Overwintering Blood Flower Indoors
Gardeners north of zone 8 can carry blood flower through winter by bringing containers indoors before the first frost. Cut the plant back by a third, move it to a bright south window or a cool garage that stays above freezing, and water sparingly until growth resumes. The plant does not need a warm room; it needs to avoid a hard freeze. The same logic builders use when insulating a tight spot, such as a low-profile attic space without removing the ceiling, applies here: a small, well-protected space holds warmth efficiently, and a garage corner above 40 degrees is enough for a dormant milkweed.
Growing From Seed
Start seed indoors six to eight weeks before the last frost: sow a quarter inch deep in moist mix, keep it at 70 to 75 degrees, and seedlings emerge in one to two weeks. Unlike many native milkweeds, tropical milkweed needs no cold stratification, making it one of the easiest species to start from seed. Harden off seedlings before setting them out.
Propagating From Cuttings
Softwood cuttings root quickly in late spring: take a 4- to 6-inch cutting from a healthy stem, remove the lower leaves, and set it in moist potting mix or a glass of water. Roots form in two to three weeks and bloom the same season, so one vigorous plant can stock an entire butterfly garden.
Pests, Diseases, and the Monarch Migration Debate
Common Pests on Milkweed
Bright yellow oleander aphids cluster on new growth, milkweed bugs feed on seed pods, and whiteflies build up on indoor plants. A strong blast of water knocks most of these down, and insecticidal soap handles stubborn colonies. Avoid broad-spectrum insecticides entirely: they kill monarch caterpillars along with the pests.
- Oleander aphids: yellow clusters on stems and buds; wash off or treat with insecticidal soap.
- Milkweed bugs: orange-and-black seed feeders; mostly cosmetic, so hand-pick or leave them.
- Whiteflies: common on overwintered indoor plants; improve airflow and use sticky traps.
Diseases and Stress Problems
Rust appears as orange pustules under leaves, and leaf spot shows up as brown blotches in humid weather; both are worse when plants are crowded or foliage stays wet. Water at the base rather than overhead and remove badly infected leaves. Yellowing foliage usually means overwatering, so check drainage before reaching for a fungicide.
Using Microclimates to Extend the Season
Warm microclimates change what a garden can grow. A south-facing wall, a paved patio, or a foundation built with insulated concrete forms absorbs heat by day and releases it at night, which can keep a marginally hardy plant alive through a mild winter; zone 7 gardeners sometimes overwinter blood flower against a warm foundation wall where it would never survive in the open bed. The same warmth feeds the monarch problem in frost-free regions, because a milkweed that never dies back keeps breeding monarchs in place all winter.
Why Tropical Milkweed Worries Monarch Scientists
Monarch researchers have raised real concerns about tropical milkweed in frost-free regions. Because blood flower stays green and blooming through fall and winter in zones 9 through 11, it can disrupt migration timing: butterflies that find blooming milkweed in November may stay and breed instead of flying to overwintering sites in Mexico. The plant can also harbor the protozoan parasite Ophryocystis elektroscirrha, whose spores build up on evergreen tropical milkweed; infected caterpillars emerge as adults with weak wings and shorter lives. Conservation groups advise planting native milkweeds such as butterfly weed, common milkweed, and swamp milkweed instead, and cutting tropical milkweed to the ground in late fall or winter where it persists, so it cannot feed late-season monarchs or accumulate parasite spores.
Treat any plant profile as a starting point rather than a promise. The same discipline that gives specifiers confidence in updated PVC profile standards for fenestration material performance applies to gardeners: compare regional trial data, check with your local extension office, and adapt general advice to your own soil, climate, and light. A milkweed planted for the wrong region does less good than the right species grown in the right place.