Blue porterweed (Stachytarpheta jamaicensis) is a fast-growing tropical subshrub native to the Caribbean and southern Florida. It produces long, wiry stems lined with small blue-purple flowers that open progressively along the spike. In frost-free zones it blooms nearly continuously and is one of the most productive butterfly and hummingbird plants available for warm-climate gardens.
Native to roadsides and disturbed ground throughout the Caribbean, it is tough and adaptable in cultivation. Full sun and good drainage are its primary requirements; it tolerates extended dry periods once established. It self-seeds freely in zones 10–11 and is documented as invasive in Hawaii and parts of the Pacific Islands, so monitoring spread is advisable outside its native range. A pH range of 6.0–7.5 suits it; sandy or loamy soils work well.
Throughout the Caribbean it is prepared as a tea - known as Brazilian tea in some regions - to treat fevers, headaches, and constipation. Ethnobotanical records document its use as a diuretic and mild laxative. Laboratory studies have identified anti-inflammatory and antimicrobial activity in leaf extracts.
These dates are for Zone 6b. Enter your ZIP to time every job to your own frost dates.
- watch · Any time in fallIn fall, clip spent flowering stems before seed set if self-seeding into surrounding beds or turf is unwanted.
- cut · Any time in winterIn zone 9b where light frost occasionally occurs, remove frost-damaged stems promptly down to healthy tissue to prevent dieback from spreading.
- cut · Any time in springCut plants back by one-third in late winter to early spring to encourage dense new growth and sustained flowering through the season.
- sow · Any time in springSurface-sow seeds in a warm, sunny spot in spring once soil temperature is reliably above 70°F; seeds need light to germinate and should not be covered.
- watch · Any time in springMonitor new growth for aphids and whiteflies, particularly during warm, humid spells with limited air circulation.
- watch · Any time in summerCheck soil drainage during heavy summer rains; standing water around the root zone promotes root rot in this species.
- cut · Any time in summerTrim back lanky stems mid-summer to keep plants compact and encourage a fresh flush of growth along new flowering stems.
Problems & troubleshooting
Common problems
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.