Blue plumbago, or Plumbago auriculata, is one of the few plants available with a true blue flower. It is native to South Africa, but can be used in the landscape as a hardy shrub in zones 8 and higher. However, in my Midwest zone 6, it is best used as an annual or in a container that can be moved indoors when cold weather strikes.
Because its semi-woody stems are somewhat floppy, it is often available in nurseries trained to grow on a trellis, but it is technically a shrub, not a vine. If left to its own devices, the stems will arch over, forming a loose mound 3-4 feet tall and wide. Either form will work in a large container, but if you would like to use Plumbago in a mixed container, training it on a trellis will allow more room for other plants, otherwise it is best to let it stand alone in a large container.
Conditions for growing plumbago
Plumbago performs best in full sun and requires good drainage. Once established, it is moderately drought tolerant. Under ideal conditions, it blooms continuously from spring through fall with blossoms that look similar to phlox, but even in less than ideal conditions, it will bloom most of the season, just maybe more sporadically. There is also a white-flowered variety, but blue is more often available. Flowers form on the current season’s growth, so don’t worry about pruning stray branches to maintain a pleasing shape. It may also be pruned heavily in late winter without reducing blooms for the upcoming season.
If Plumbago foliage starts to yellow, it may be a symptom of manganese deficiency, which can be easily corrected by applying a fertilizer that contains manganese sulfate. It prefers slightly acidic soil, so fertilizers made for acid-loving plants like azaleas and holly work well and can be mixed into potting soil at planting time. To maximize blooms, fertilize throughout the growing season with a bloom-boosting fertilizer (i.e. one with a high middle number like 15-30-15 or something similar).
Plumbago may survive a light frost, but may also die back to the ground, so if you live in a zone with cold winters and want to keep your plumbago alive, either move it indoors to a bright location for the winter and treat as a houseplant or cut it back and place it in a cool dark corner of a basement or garage where temperatures won’t drop below 45 degrees Fahrenheit. Either way, water sparingly. Move it back out in the spring when the threat of frost has passed and enjoy another year of bountiful blue blooms!