In this article, we talk about how to care for plumbago, a beautiful flowering shrub that thrives in tropical climates. This plant also makes a pretty houseplant if you don’t have the warm temperatures it prefers.
I. Appearnce and Characteristics
Plumbago is a genus of 23 species of flowering plants in the family Plumbaginaceae, native to warm temperate to tropical regions of the world. Common names include plumbago and leadwort (names which are also shared by the genus Ceratostigma).
The generic name, derived from the Latin words plumbum (“lead”) and agere (“to resemble”), was first used by Pliny the Elder (23-79) for a plant known as μολύβδαινα (molybdaina) to Pedanius Dioscorides (ca. 40-90). This may have referred to its lead-blue flower colour, the ability of the sap to create lead-colored stains on skin, or Pliny’s belief that the plant was a cure for lead poisoning.
The species include herbaceous plants and shrubs growing to 0.5–2 m (1.6–6.6 ft) tall. The leaves are spirally arranged, simple, entire, 0.5–12 cm (0.20–4.72 in) long, with a tapered base and often with a hairy margin. The flowers are white, blue, purple, red, or pink, with a tubular corolla with five petal-like lobes; they are produced in racemes.
The flower calyx has glandular trichomes (hairs), which secrete a sticky mucilage that is capable of trapping and killing insects; it is unclear what the purpose of these trichomes is; protection from pollination by way of “crawlers” (ants and other insects that typically do not transfer pollen between individual plants), or possible protocarnivory.
Mature plumbago leaves often have a whitish residue on their undersides, a feature that can confuse gardeners. While this white material resembles a powdery mildew disease or a chemical spray deposit, it is actually a natural exudate from “chalk” glands that are found on the Plumbago species.
II. How to Grow and Care
Sunlight
Plumbago looks its best when it has access to full sunlight for at least six hours. It will prefer even more than that, so give it as much as possible. If grown indoors, keep them by a sunny window or give them a grow light.
When you’re hardening off new seedlings, they must be in full shade if they’re outdoors. Keep tender plants moist so the sun’s heat doesn’t dry them out or burn their leaves.
Climate and Temperature
A skilled gardener dressed in a red flannel shirt and white gloves, gently holding a large black pot brimming with exquisite blue plumbago flowers and lush green leaves. Behind is another gardener and a lush backdrop of verdant leaves.
Plumbago is sure to be happy in USDA zones 9-11, though you may find some success in zone 8 if you can protect your plant from freezing temperatures. If winter dips below 20°F in your zone, you must keep your plant in a container and bring it inside during the cold months.
Plumbago is native to tropical regions that receive plenty of rain. If you can provide warm weather and moist soil, you can grow this plant with few problems. You can achieve this indoors with grow lights and heating mats or use a greenhouse.
Watering
Keep your plumbago in moist soil, ensuring that water can never puddle and that there’s good drainage. One inch of water per week should suffice, but you may need to increase this during drought or excessive heat. This is especially important for young seedlings and plants you’re hardening off.
Established plants that have been in the garden for at least a year can tolerate slight drought conditions, but you should try to prevent that the best you can if you want the plant to thrive.
Indoor plants typically require less water. Container plants kept outside or in greenhouses often need to be watered more frequently since container soil dries out quickly.
Soil
Plumbago is pretty tolerant of most soils, though it thrives in sandy soil that drains well. Avoid heavy clay soils since they don’t drain well, or amend them with sand to create a loamy texture.
It prefers a neutral pH of 6.0-8.0 but tolerates mildly acidic or alkaline soils. However, a pH over 8.0 (alkaline soil) may cause a nutrient deficiency, resulting in yellow leaves.
These shrubs have a tolerance for salt since they come from tropical regions. They can tolerate salty, sandy soils if you live near the ocean.
Fertilizing
Give your plant as much organic matter as possible. A fresh layer of compost mixed into the soil once or twice a month will help the plant stay healthy and continue flowering. If your plant doesn’t flower all year, you can limit compost refreshing to the growing season.
You can also give your plant a slow-release fertilizer in early spring. Choose a general all-purpose fertilizer or a product designed for shrubs. Granules only need to be applied once yearly unless specified otherwise on the packaging.
Planting Instructions
Pruning
Plumbago will let you prune it any time of year with no problems, making it easy to care for. Every spring, trim back any branches damaged by frost. Throughout the year, prune excess and unruly growth as needed.
Pruning isn’t a requirement unless your shrub starts to take over. If desired, train it up fences and trellises to help keep it contained. Container plants will be much smaller than ones in the ground outside, so if you don’t have room for a giant shrub, consider growing it in a container.
Propagation
Seeds
Getting plumbago seeds to grow successfully in your garden is super easy. Seeds are ready to harvest once the flowers dry up. You’ll see them hanging on the plant where the flower used to be. If you’re planting for the first time, you can find seeds online.
In late spring or early summer, use 4-inch seed-starting containers with a loose growing medium so the seedlings can easily root. Plant the seeds ¼ inch deep, with only one or two seeds in each container. Place the seeds in a sunny window or under a grow light.
Keep the soil moist but not soggy. The seedlings should sprout within four weeks. If multiple seeds sprout, thin them out so only one remains. Harden them off (expose them gradually to outdoor temperatures) before transplanting them outside.
Root Cuttings
You can also propagate plumbago via root cuttings. While slightly more difficult than taking stem cuttings, the success rate is usually higher.
Start with a 2 or 3-year-old plant to ensure it has mature roots. If the plant is too young, you risk injuring it and having unsuccessful cuttings.
Dig around the mother plant until you find a clump of roots that are ¼ to ½ inch in diameter, and remove them from the plant. Use sharp tools to remove the entire clump and not just the roots so you don’t damage the plant.
Cut the roots into 4 to 6-inch sections. Prepare a shallow tray or container of soil, lay the root sections on top, and then cover them with a half-inch of soil. Keep the soil moist and place the cutting in a sunny location; grow lights also work well.
New shoots should develop in two or three weeks. Wait four weeks before transferring the seedlings to their own containers. Once the plants have established themselves in their new containers, you can harden off the plants to prepare them for the outdoors.
Stem Cuttings
Stem cuttings are much easier to obtain than root cuttings, but their success rate isn’t as high. Take several cuttings at a time in case some fail.
A major benefit of taking stem cuttings is you don’t need a mature plant to get started. Regardless of the plant’s age, choose new growth that’s still flexible. You can choose older growth, but ensure it’s not flowering, or it won’t take root.
Wait until late spring to take a cutting. Cut the stem to three or four inches long with two leaf nodes, cutting just above a pair of leaves to remove it from the plant.
Then, cut the stem below the bottom set of leaves and remove the leaves. You can leave the leaves on top—just make sure it’s only a node at the bottom.
Soak the node in water, and dip the cut end in a powdered rooting hormone after soaking for the best results. Choose a container at least as deep as the stem, and make a small hole with a pencil or stick. Bury the stem so that the leaves are sticking out from the soil.
Keep the soil moist and the plant in indirect sunlight. Direct sunlight will evaporate water too quickly and create too much heat for the plant. You can leave the cutting outside, but ensure it’s in full shade. A plastic bag over the top will help retain moisture, but remove the bag and wipe out condensation every so often to remove excess moisture.
Stem cuttings will take about one month to develop roots, and you should wait another two months to plant them outside. Plant them in the fall or overwinter them inside for spring planting.
Division
Clump division will be stressful for the plant but easy for you. If you go this route, be extra careful when handling the plant. Wait for autumn when the temperatures cool down, and all the flowers finish flowering. Only divide clumps from a two or three-year-old plant so its mature roots will have a better chance of acclimating.
Water your plant deeply the night before you divide it so its roots are well-watered and easy to remove. When it’s time to divide, identify a root clump and how far the roots stretch. Clumps should have three to five stems. Try to pick new growth, as hardwood stems will likely not survive the transplant.
Use a sharp trowel or spade and try to keep three inches of soil around the clump to prevent damaging small roots. Place the plant in a hole the size of the root ball, backfill it with soil, and add an inch or two of mulch to protect it and keep it watered.
Don’t plant divided clumps closer than three feet from another plumbago plant, and keep the plant well-watered until it’s about a year old.
Layering
Layering, or marcotting, is preferred for laidback gardeners who want to work smarter and not harder. It has a high success rate, but you’ll have to have the new plant next to the old one or transfer it to a container before planting it elsewhere in your garden. This method involves taking a flexible branch, bending it to the ground, burying it, and waiting for it to take root and develop new growth.
Autumn is the best time for this method because the new plant won’t have to battle the hot sun while it establishes in your garden.
Start by clearing the ground and lightly tilling it, or prepare a container by filling it with soil. Pick a long new branch that can bend without snapping. It will work well if you can bend it into a U shape.
Make a small cut lengthwise on the branch, no more than an inch long. Leave enough room between the mother plant and the cut so the plant will have enough room to grow. Don’t make a deep cut; all you need to do is score it. Then, apply a rooting hormone to the cut you made.
Bury the cut stem about two inches deep in the soil, whether that’s in the ground or in a container. Stake up the part of the stem that isn’t attached to the mother plant so it will grow straight up. If you skip staking it, your plant may not grow where you wanted it.
Keep the plant moist but not wet for the following months. If the new plant has established roots in the spring, cut the stem attached to the mother plant. If you put your plant in a container, you can move it to wherever you’d like.
When planting it in the ground, ensure it’s well-established before doing so. Otherwise, you’ll risk stressing and potentially killing your young plant.
Pests and Diseases
Plumbago doesn’t have any major disease problems, though there are a few pests that might bug them. Fortunately, you can prevent and treat them without hurting your shrub.
- Cotton Cushion Scale
The cotton cushion scale (sometimes called cottony cushion scale) is named for its cotton-like appearance. The scales range from orange to brown, but the egg sac has a cotton appearance. If you see puffy white bumps all over your plumbago, you may have a big problem.
Scales eat the sap out of shrubs and trees. They can cause discoloration or deformation of stems and leaves, and large infestations could kill the plant.
Two predatory insects will help control your cotton problem: the Vedalia beetle and the parasitic fly. The vedalia beetle is a type of ladybug that lays its eggs on the scale. The ladybug larvae feast on the contents of the egg sac. The parasitic fly behaves similarly by laying eggs in scale larvae, which the fly larvae will eat their way out of. (Nature is pretty gross, isn’t it?)
If you have cotton cushion scale, you probably have an ant problem. Scales create honeydew, which ants love. Ants will turn your shrub into a scale farm and will keep them around so they can enjoy the sugary goodness. Keep ants away with cinnamon, wash them off with water, or revert to harsher means with chemical pesticides for ants.
Prevent the scale problem by ensuring your plant has plenty of airflow. They thrive in cool, moist conditions, so removing enough branches to let the sunlight in and letting your plants stay on the dry side helps clear them out.
For large pest problems, use pyrethrin sprays. However, avoid using pesticides if you see evidence of ladybugs or parasitic flies. Fighting these pests biologically should be enough because pesticides kill all bugs, whether good or bad.
- Spider Mites
A close-up of two spider mites on a veiny green leaf. The first spider mite is small, with a body that appears translucent yellow. The second mite is larger with a combination of a brown body and translucent legs.
Mites are another plant-sucking problem that will hurt your plumbago. The bad part of this pest is that you probably won’t see them until they’ve already damaged your plant. They’re so tiny that you’ll probably need a magnifying glass to see them.
You’ll notice spider mite damage when you see small brown dots on the leaves. The leaves will turn yellow or red and then drop off the plant. Lost leaves shouldn’t hurt the plant unless it’s young or loses many leaves at once.
Thorough watering is the best way to prevent mite damage since stress can make plants more susceptible.
Many insects eat spider mites, including predatory mites, predatory six-spotted thrips, lacewing larvae, and the spider mite destroyer lady beetle, a tiny solid black ladybug. If you see these insects in your garden, leave them be! They’re helping you out.
If predatory insects aren’t helping, wash mites off with water or spray them with neem oil or insecticidal soap as a natural means to eliminate them. They need the leaf sap to survive, so washing them off will help kill them. Neem oil and insecticidal soap will suffocate them and greatly harm their population.
Pesticides are also an option if natural means aren’t working. Look for options designed for mite control. Remember that these chemicals will harm other insects, including beneficial insects like predators and pollinators.
- Thrips
Thrips are small insects that can be yellow, black, or brown. They also suck sap from leaves that will result in spotted or curling leaves, eventually stunting plant growth. Thrips are easier to spot with mites, though you may not notice them until you have visible leaf damage.
Wash thrips off with water or use insecticidal soap or neem oil to get rid of them naturally, or you can let predatory mites eat them.
Chemical control usually comes in the form of an all-purpose pesticide for shrubs. This type of pesticide usually kills thrips, mites, and many other insects. It may harm beneficial bugs, though, so be careful when you apply them to your shrubs.
III. Uses and Benefits
Often featuring large clusters of showy flowers, several plumbago are cultivated as ornamentals, particularly in parks and gardens boasting mild climates.
