Q: Why is my plumbago shrub not doing well? I have seen the one in the UF/IFAS Nassau County Demonstration Garden and the ones at your Yulee satellite office. They all look beautiful. What am I doing wrong?
A: It helped to have a clipping of your shrub because I was able to detect mites which contributed to the shrub’s decline. Consider some light pruning to remove heavy infestations on the limb tips along with horticulture oil sprayed directly on the plant leaves and stems. In addition, applying imidacloprid as a soil drench around the root area should help you control the mites. This chemical is taken up by the roots and goes through the vascular system ending up in the leaves and flowers. When the insect feeds on the plant tissue they take up the chemical and die. We would not recommend you use this on all your plants but only those having insect infestations. Both the horticulture oil and imidacloprid can be found at most any garden center.
Plumbago, Plumbago auriculata, is best grown in zones 9-11. Remember those of you along the east part of I-95 are in cold hardiness zone 9a while those of you on the west part are in 8b. This means plumbago may die back completely if temperatures become too cold for long periods of time. In your case, since you are in zone 8b, this plant is slightly out of its comfort zone. This may place some undue stress on the plant making it may be more susceptible to insects or disease. But do not be discouraged as it may well survive in your area although it does have one strike against it. Be sure to protect plumbago if temperatures drop below 32 degrees, especially during its first few years in the ground. Allow for plenty of room as it can reach heights of up to 10 feet with an equal spread. This makes it a poor specimen for directly up against the house.
Plumbago prefers part shade to part sun but I have seen it planted in full sun with some success too. Its periwinkle blue flowers are unusual in the plant kingdom making it a prized plant. The flowers bloom from spring through the fall. Plumbago is slightly drought tolerant but does not need to be watered as often as lawn grass. It can live in most any soil condition making a wonderful plant for new home sites. However, if the soil pH is too alkaline the leaves will turn yellow from mineral deficiencies. There is a white flowered plumbago cultivar called ‘Alba’.
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