Blue plumbago or blue cape leadwort is a delightful sprawling shrub that’s covered with sky-blue phlox-like flowers much of the year. Here’s how to grow and care for this African native.
Blue plumbago (Plumbago auriculata) is an unusually soft, pretty shrub for desert gardens. With lush, true green foliage and sky blue flowers, it looks like it belongs in a temperate garden or the tropics. But when planted in the right location with the right care, it is perfectly happy growing in desert gardens.
This plant is not quite a vine and not quite a shrub. In fact, depending on how you trim it, you can grow it as a vine, shrub, or ground cover.
Why I Like This Plant
- Lush evergreen shrub
- Sky-blue flowers are rare in the desert palette
- Attracts butterflies
Things to Watch Out For
- It’s not reliably evergreen in the southwest
- All parts are toxic and touching it can cause contact dermatitis
- Our alkaline desert soil is not its preferred soil type
Optimal Growing Conditions
If you’re thinking of adding a blue plumbago to your garden, you need to find a suitable place that will keep your plant healthy and looking good… while minimizing maintenance for you.
Here are the key factors to keep in mind.
Temperature
Blue Plumbago should be grown in USDA Hardiness Zones 9 – 11. It is cold-hardy and evergreen to 25°F. The top may die back if it gets colder, but it is reportedly root-hardy to 10°F.
Sun Exposure
Plant it where it will receive either dappled shade or afternoon shade during the summer. Too much heat or sun will blanch the blue flowers to near-white.
Size and Growth Rate
Blue plumbago is a moderately fast grower that typically reaches a size of 6 feet high by 10 feet wide.
Soil
It grows well in most well-draining soils, however, our highly alkaline (high pH) desert soils are not ideal. If your leaves turn yellow, it’s likely because your soil is too alkaline. This can be remedied with a soil acidifier.
Another option if your soil is too alkaline, is to grow it in a pot. Its sprawling, cascading shape makes it an excellent candidate for growing in large or tall containers.
Other Location Considerations
All parts (bark, foliage, fruit, pollen, roots, sap, seeds) of plumbago are toxic, so don’t plant it where kids or pets can get at it. It can irritate your skin and eyes, and is harmful if ingested.
Blue plumbago’s sprawling nature makes it a good groundcover, bank cover, or container plant.
Blue Plumbago:
The Essentials
| Common Names | Blue plumbago, cape plumbago, leadwort |
| Scientific Name | Plumbago auriculata |
| Origin | Southern Africa |
| Plant Type | Semi-deciduous shrub |
| USDA Zones | Zones 9 – 11 |
| Cold Hardiness | To 25°F |
| Flower Color | Blue |
| Flower Season | Spring, summer, fall |
| Mature Size | 6’ high x 10’ wide |
| Growth Rate | Moderate |
| Sun Tolerance | Full, part sun |
| Water Needs | Moderate |
| Pests & Diseases | Iron chlorosis |
| Toxicity | All parts toxic |
| Wildlife | Attracts butterflies Deer, rabbit, javelina resistant |
How to Plant
The rule of thumb when planting any shrub or tree in the desert is to dig a hole three times as wide as the root ball but no deeper. Amending the soil is not recommended. Counterintuitively, backfilling with the same native soil you just dug up helps your plant develop a stronger root system.
When to Plant
The best time to plant plumbago is in the fall. This gives your shrub three seasons to grow roots and get established before the following summer.
The second best time is in spring, the earlier the better. This still gives your plant time to get established before the intense heat of June arrives.
How to Care for Blue Plumbago
Whether you’ve recently planted a plumbago or have an existing plant in your yard, here’s how to take care of it to keep it healthy and looking its best.
How to Water New Plants
Once you’ve got your plumbago in the ground, watering is your most immediate concern. Here is the recommended watering schedule for new shrubs planted in the spring or fall.
| Weeks 1 & 2 | Every 3 – 4 days |
| Weeks 3 & 4 | Every 6 – 7 days |
| Weeks 5 & 6 | Every 7 – 10 days |
| Weeks 7 & 8 | Every 10 – 14 days |
After week 8, gradually extend the time between waterings.
How to Water Established Plants
As your shrub gets established, there are two watering factors to consider.
- First is how often to water. This will vary with the seasons.
- Second is how much water to give your shrub with each watering. This depends on the current size of your plant.
To determine the ideal watering schedule for any desert shrub you’ll find everything you need to know, including easy-to-use charts, at How to Water Desert Shrubs: How Often? How Much?
Note that when given too much water, blue plumbago will develop more leaves at the expense of flowers.
Should You Fertilize?
There is normally no need to fertilize plumbago. They usually get all the nutrients they need from our mineral-rich native soil.
However, if your plant’s leaves are turning yellow, it may have iron chlorosis. You can address this by adding an iron plus soil acidifier fertilizer.
If you grow one in a pot, fertilize lightly a few times a year when it’s actively growing.
How to Prune
Blue plumbago is an informal accent shrub that looks its best when allowed to sprawl or cascade. If you try to shear it like a hedge or take a bit off all the ends, you will destroy the shape and inhibit flowering.
Its foliage is not frost-hardy, so it often dies back every winter. This makes pruning easy. Simply cut it down to the ground every spring after the last freeze. Since it is a skin irritant, wear gloves and protective clothing when handling.
Blue Plumbago Cultivars
Blue plumbago has several popular varieties you may encounter when plant shopping.
Plumbago auriculata ‘Imperial Blue’ Civano Select ™‘ is a vigorous, vining shrub that can grow up to 10 feet. According to Tucson’s Civano Nursery, “Taming this shrub requires some work” so give it plenty of space.
Plumbago auriculata ‘Monott’ is a more compact version that grows to be 5 feet tall and 6 feet wide. Its deep blue flowers are less prone to fading in the heat of summer.
Plumbago auriculata ‘Dark Blue’ grows best in rich soil kept consistently moist. For these reasons, it’s best grown in containers in the desert southwest.
There is also a white plumbago (Plumbago auriculata ‘Alba’) cultivar. It is somewhat smaller, less robust, and has white rather than blue flowers.
Plant-Lover Facts
Blue plumbago (Plumbago auriculata) is native to parts of southern and southeastern Africa, but it has naturalized in isolated areas of most continents, including Florida and Mexico.
No one is certain how plumbago got its name, but most likely its common names leadwort and plumbago (‘’plumbum” means “lead” in Latin) derive from the fact that it was thought to cure lead poisoning.
In France, this shrub is called “dentelaire” because it was traditionally used to relieve toothache.
Plumbago is thought to be a distant ancestor of carnivorous plants. Plumbago’s flowers have sticky sepals that work much like Velcro to capture insects. Additionally, plumbago contains plumbagin, a unique toxic compound also found in carnivorous plants. Plumbagin is currently being studied as a potential treatment for many types of cancers.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
Photo Credit
Yercaud-elango, CC BY-SA 4.0, Wikimedia Commons