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.
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.