Cuphea viscosissima aka Clammy Cuphea

Cuphea viscosissima is an annual in the loosestrife family, Lythraceae. Its common names include blue waxweed, clammy cuphea, and tarweed. It comes from the eastern and central United States. Its range spans parts of the Northeast, Midwest, and South. It is not native to Britain or Ireland. Garden sources describe it as an annual, though one archived record calls it perennial.

The plant forms a bushy clump with spreading branches. RHS gives a height range of 0.3–1.6 feet [0.1–0.5 metres]. Its stated spread is 1.6–3.3 feet [0.5–1 metre]. Both its leaves and stems feel sticky. Purple to purple-red flowers provide colour from July to October. This long season carries the display from summer into autumn. The flowers draw butterflies and hummingbirds to the garden.

Grow it in soil that drains well, in a sheltered spot. Full sun suits it, but RHS also allows partial shade. Shade from hot sun can help in warmer positions. Chalk, loam, and sandy soils all suit the plant. It accepts acid, neutral, and alkaline soil. RHS lists dry to moist conditions; Missouri Botanical Garden gives medium water needs. RHS rates it H2, so it cannot survive freezing. Missouri Botanical Garden lists USDA zones 6–9 for this annual.

Use it in flower beds, borders, or along paths. Its spreading form also suits pots on patios and porches. RHS includes city gardens, courtyards, and borders beside walls among its uses. Missouri Botanical Garden suggests meadows and other informal planting areas. It also fits butterfly gardens, where its flowers draw visiting insects. Raise plants from seed, preferably sown where they will flower. RHS says it needs no pruning. Missouri Botanical Garden rates its upkeep as low.

Serious pest and disease problems are not a main concern. RHS reports few problems with either pests or disease. Leaf spot can occur, according to Missouri Botanical Garden. Plants for a Future records no known hazards. That report does not establish that every part is safe to eat. It notes potential use as an oilseed crop. This is not evidence for eating the leaves or flowers. The same source lists no known medicinal uses or weed concern.