Cape plumbago

About Cape plumbago

Cape plumbago is a sprawling evergreen shrub from southern Africa with clusters of phlox-like flowers in a rare sky blue (or white). It shrugs off heat and drought, blooms from late spring to frost, draws butterflies and is a host plant for the cassius blue butterfly (UGA; UF/IFAS). It's a shrub or cascading mass planting in the far South and a container plant or annual farther north; it was named a Texas Superstar plant in 2005.

Evergreen in zones 9-11 (NC State, UF/IFAS); root-hardy to about zone 8b, where a freeze kills it back but it usually regrows in spring (UGA, UF/IFAS). Grown as an annual or overwintered indoors farther north. UF/IFAS rates it not a problem species in Florida.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Plant nursery plants in spring after frost; give mass plantings 4-6 ft so the arching stems can spread (UF/IFAS). In zone 8 add an extra layer of winter mulch over the roots (UGA). Farther north, grow it in a pot and bring it into a bright, sunny room for winter, or cut it back and keep it in a cool, dark place with little water (NC State). Days to first bloom aren't documented.

Soil

Well-drained soil of almost any type; in alkaline (high pH) soil the leaves may yellow from mineral shortages (UF/IFAS, UGA).

Any well-drained soil works; avoid very alkaline spots, where leaves may yellow (UF/IFAS).

Feeding

• Growing season (spring into summer): general-purpose shrub fertilizer. UF/IFAS says it responds well to one or two fertilizer applications a season; follow the label and a soil test.

Shearing it as a tight hedge removes most of the flowers, since it blooms on new growth (UF/IFAS).

Harvest

Blooms on new growth from late spring until frost, and almost all year in central and south Florida (UGA, UF/IFAS). Cut back leggy stems to bring on more flowers, and prune freeze-damaged growth in spring (UGA, UF/IFAS).

Varieties (3)

Extension sources document only 2 cape plumbago cultivars plus the native white doctorbush.

Good neighbors

Petunia, Coleus, Salvia (ornamental sage)

UGA suggests pink petunias, orange coleus and 'Black and Blue' salvia as color partners in beds and pots; that's a design pairing, not a tested pest benefit.

Pests to watch for

Thrips, Scale insects, Twospotted spider mite

Diseases and problems

Nutrient deficiency

In the kitchen

Safety: All parts contain plumbagin, a skin irritant: the sap can cause redness and blisters, so wear gloves when pruning (NC State). Don't eat any part.

Pets: Not listed by the ASPCA (its plumbago entries are Ceratostigma, a different plant). NC State rates cape plumbago as poisonous with medium severity, so keep pets from chewing it.