Shrub
Cape plumbago
Plumbago auriculata · Plumbaginaceae
Also called: Plumbago, Cape leadwort, Blue plumbago, Skyflower
Cape plumbago (Plumbago auriculata) is a low-water shrub well suited to Tucson and the low desert. It thrives in full sun to part shade.
Cape plumbago at a glance
- Water use
- Low (established)
- Sun
- Full sun to part shade. In Tucson it flowers best in full sun but appreciates afternoon or filtered shade in the hottest reflected-heat sites; can scorch in extreme west-facing exposures.
- Mature size
- Mounding/sprawling evergreen shrub 4-6 ft. tall and 6-10 ft. wide (can climb/scramble higher with support).
- Growth rate
- Fast.
- Bloom
- Sky-blue to pale blue (white-flowered forms exist), in phlox-like clusters., Spring through fall, peaking in the warm months; blooms nearly year-round in mild Tucson winters.
- Cold hardiness
- Frost-sensitive: foliage damaged below ~25-28°F and can freeze to the ground in hard Tucson freezes, but recovers quickly from the roots in spring. Root-hardy in USDA 9a-9b; protect in unusually cold snaps.
- Soil
- Prefers well-drained soil; tolerates poor, alkaline desert soils though it slightly prefers acidic conditions - amend with compost and watch for iron chlorosis.
- Native range
- South Africa (Cape region)
- Best used as
- Informal flowering hedge or screen, Mass planting on slopes/banks, Large container plant, Espalier or scramble over walls/fences, Pollinator and butterfly gardens, Filler in transition/mini-oasis zones
- Wildlife
- A magnet for butterflies (larval/nectar plant for some skippers and the Marine/Cassius blue) and bees; provides long-season nectar.
- Toxicity
- Mildly toxic - sap and foliage can cause skin irritation/contact dermatitis, and ingestion may cause mouth and stomach irritation in pets and children. Wear gloves when pruning.
How to grow Cape plumbago in Tucson & the low desert
Watering
Moderately drought tolerant once established but blooms and looks best with regular water. In Tucson, water deeply about weekly in summer, every 10-14 days in spring/fall, and roughly monthly in winter. Needs good drainage.
Fertilizer & nutrients
Apply a balanced controlled-release fertilizer in early spring to drive growth and bloom; a second feeding in summer helps. In alkaline desert soils, add chelated iron if foliage yellows (chlorosis).
Pruning & care
Fast-growing and rangy - shear or head back hard in late winter (after frost danger) to control size and renew. Tip-prune through the growing season to shape and keep dense; tolerates hard rejuvenation pruning.
Notes
Reliable, long-blooming blue-flowered shrub for Tucson, valued because true blue flowers are rare in desert plants. Sprawls and self-layers; give it room or plan to prune. Sites with some afternoon shade and good drainage perform best. The sticky seed capsules can cling to clothing and pets.
Sources: Arizona-Sonora Desert Museum plant care sheet - Plumbago auriculata (desertmuseum.org/visit/sheets/Pluaur.pdf); AMWUA / Water Use It Wisely (wateruseitwisely.com); University of Arizona / Pima County Cooperative Extension