Oleander is a tough shrub that shrugs off heat, drought, and poor soil, and most of what goes wrong with it is cosmetic or easy to fix. Sticky leaves, knobby growths, a few frost-browned branches, or a summer without flowers usually point to a cause you can deal with. One disease is different: a bacterial infection carried by insects that slowly kills the shrub and has no cure. Oleander is also highly poisonous, so even routine pruning comes with its own precautions.
Sticky Leaves and Black Mold From Aphids and Scale
Clusters of bright yellow insects on tender shoots and buds are oleander aphids, which suck sap through slender, threadlike mouthparts.1NC State Extension Publications. Oleander Aphid As they feed they drip honeydew, a sweet, sticky liquid that coats the leaves below.2NC State Extension Publications. Oleander Aphid Dark fungi called sooty mold grow on the honeydew, leaving the plant covered in yellow aphids, cast skins, sticky residue, and black mold.3NC State Extension Publications. Oleander Aphid
Scale insects cause the same mess but are harder to spot. False oleander scale is the top scale pest on ornamental plants in Florida and attacks more than 50 kinds of plants.4Florida State Horticultural Society. Management of the False Oleander Scale, Pseudaulacaspis cockerelli (Cooley) Females sit scattered on the upper side of leaves and on green young stems, while males crowd together on leaf undersides.5Florida State Horticultural Society. Management of the False Oleander Scale, Pseudaulacaspis cockerelli (Cooley) Their feeding weakens the plant and leaves yellow patches where they feed.6Florida State Horticultural Society. Management of the False Oleander Scale, Pseudaulacaspis cockerelli (Cooley) Scale also give off sticky residue, so black mold follows them too.7Florida State Horticultural Society. Management of the False Oleander Scale, Pseudaulacaspis cockerelli (Cooley)
To tell the two apart, look at what the insects are doing. Aphids are soft, bright yellow-orange, and cluster on new shoots and buds. Scale look like tiny flat bumps or flecks stuck to leaves and stems, and once settled they stay put.
Hoverflies, ladybeetles, and lacewings are the main predators that eat oleander aphids.8Horticulturae. Contribution of Surrounding Flowering Plants to Reduce Abundance of Aphis nerii (Hemiptera: Aphididae) on Oleanders (Nerium oleander L.) Surrounding oleanders with flowering plants such as sweet alyssum, marigold, or yarrow draws in more of them and can reduce aphid numbers.9Horticulturae. Contribution of Surrounding Flowering Plants to Reduce Abundance of Aphis nerii (Hemiptera: Aphididae) on Oleanders (Nerium oleander L.) The benefit builds slowly, though; in one long trial it took until the fourth year to show clearly.10Horticulturae. Contribution of Surrounding Flowering Plants to Reduce Abundance of Aphis nerii (Hemiptera: Aphididae) on Oleanders (Nerium oleander L.) Use quicker controls for heavy outbreaks now.
A strong spray of water knocks aphids off shoots, and you can repeat it every few days. Insecticidal soap or horticultural oil works on contact, so coverage of leaf undersides matters. Avoid broad-spectrum insecticides, which also kill the ladybeetles and lacewings that help you. Heavily infested shoots can simply be pruned off; wear gloves, because the sap is toxic.
Once the insects are gone, black mold washes off with water or a mild soapy spray. If new mold keeps appearing, insects are still active.
Knobby Galls on Stems, Buds, and Leaves
A bacterium causes distorted, swollen, knot-like growths on oleander stems and bark, a problem known as oleander knot.11UC IPM. Common Problems With Oleander and How to Handle Them On oleander it can also form galls on flower buds and leaves.12UC IPM. Common Problems With Oleander and How to Handle Them Galled branches often die back, but the overall health of the plant is usually not seriously threatened.13UC IPM. Common Problems With Oleander and How to Handle Them Galls take weeks to appear; on young oleanders infected on purpose, knots showed up about 46 days later.14Open Journal of Bacteriology. Carrot slice test: A reliable method for evaluating the tumorigenicity of Pseudomonas savastanoi pv. nerii
The bacteria enter through wounds such as pruning cuts or frost cracks, so the knots you see now may trace back to a pruning job you’ve forgotten. Avoiding unnecessary wounds is the best prevention.
To remove galls, cut galled shoots several inches below the swelling, into healthy wood. Wipe your pruners with rubbing alcohol or diluted bleach between cuts so you don’t carry bacteria to new wounds. Prune in dry weather, since splashing water pushes bacteria into fresh cuts. Bag and discard the galled pieces rather than composting them.
Oleander Leaf Scorch, the One Disease That Kills
Oleander leaf scorch is caused by a strain of the bacterium Xylella fastidiosa.15HortScience. Transmission of Xylella fastidiosa to Oleander by the Glassywinged Sharpshooter, Homalodisca coagulata It lives in the plant’s water-conducting tissue, where it blocks water flow to the leaves. Leaves yellow and then brown from the tips and edges inward, starting on one or a few branches and spreading through the plant over a few years. Frost or drought hits the whole plant at once, but scorch moves branch by branch and doesn’t respond to watering. A local extension office or plant lab can test a sample to confirm.
The bacterium spreads when sap-feeding leafhoppers feed on an infected oleander and then on a healthy one.16PubMed. Causal Role of Xylella fastidiosa in Oleander Leaf Scorch Disease At least three kinds of these leafhoppers have been shown to pass it between oleanders.17PubMed. Causal Role of Xylella fastidiosa in Oleander Leaf Scorch Disease The glassy-winged sharpshooter, a large leafhopper, is a main carrier in California.18HortScience. Transmission of Xylella fastidiosa to Oleander by the Glassywinged Sharpshooter, Homalodisca coagulata
No cure or spray clears the bacterium. Pruning out browned branches may make the plant look better for a while, but it doesn’t stop the disease. Removing infected shrubs, roots included, protects nearby oleanders. When replanting, consider a different shrub if scorch is common in your area.
Root Rot From Too Much Water
Phytophthora, a water mold, causes root rot and dieback across many shrubs and garden plants.19Crop Timeline for Nursery-Grown Evergreens and Shade Trees. Crop Timeline for Nursery-Grown Evergreens and Shade Trees Overwatering has to be avoided to manage it.20Crop Timeline for Nursery-Grown Evergreens and Shade Trees. Crop Timeline for Nursery-Grown Evergreens and Shade Trees21Crop Timeline for Nursery-Grown Evergreens and Shade Trees. Crop Timeline for Nursery-Grown Evergreens and Shade Trees22Crop Timeline for Nursery-Grown Evergreens and Shade Trees. Crop Timeline for Nursery-Grown Evergreens and Shade Trees Oleander tolerates drought, so it is more often harmed by too much water than too little.
Check for a plant that wilts or yellows even though the soil is moist. Dig carefully and look at the roots: healthy ones are firm and pale, while rotted ones are dark, soft, and mushy. Problems are worst in low spots, clay soil, and pots without drainage holes.
Let the top few inches of soil dry before watering an established oleander. Make sure pots have drainage holes and never sit in a saucer of water. Keep irrigation from constantly spraying the base of the shrub. In heavy soil, plant on a slight mound so water drains away.
Cold Damage and How Much Frost Oleander Can Take
- Above about 15 to 20°F: most oleanders survive winter unharmed.23eHow. Common Problems With Oleander and How to Handle Them
- Below 15°F: more and more leaves and branches die.24eHow. Common Problems With Oleander and How to Handle Them
- Dwarf oleanders: damaged earlier, at about 20°F.25eHow. Common Problems With Oleander and How to Handle Them
- Below 10°F: the plant can die to the ground and the roots may die too, so it won’t regrow.26eHow. Common Problems With Oleander and How to Handle Them
The longer a cold spell lasts, the more dieback to expect.27eHow. Common Problems With Oleander and How to Handle Them Varieties differ as well: in one trial a few hours at about 25°F didn’t affect a yellow-flowered oleander but harmed a pink one.28HortScience. Determining Freezing Injury from Changes in Chlorophyll Fluorescence in Potted Oleander Plants Some plants recovered from freeze stress over the following 4 months.29HortScience. Determining Freezing Injury from Changes in Chlorophyll Fluorescence in Potted Oleander Plants So wait until new growth appears in spring before cutting back frozen branches.
Brown, crisp leaves after a freeze don’t mean the whole plant is dead. Scratch the bark: green underneath means the stem is alive. Once spring growth starts, cut dead wood back to living tissue. Expect fewer flowers that year, because pruning removes wood that would have bloomed.
Before a freeze, water the soil, since moist soil holds heat better than dry. Cover shrubs with frost cloth that reaches the ground, and take it off in the daytime. Potted plants can move into a garage or porch during hard freezes.
Salty Water and Burned Leaf Edges
Oleander blocks salt from reaching its leaves more effectively than most non-salt-loving plants, keeping more in its roots.30PubMed Central. Effects of salinity and drought on growth, ionic relations, compatible solutes and activation of antioxidant systems in oleander (Nerium oleander L.) Even so, salty irrigation can cause leaf salt symptoms, leaf drop, smaller leaves, and less root growth.31European Journal of Horticultural Science. Paclobutrazol as an aid to reduce some effects of salt stress in oleander seedlings Browning leaf edges on a seaside or salty-water planting often point to salt.
Water deeply and less often to wash salt below the roots. Keep road-salt runoff and pool backwash away from plantings. For potted oleanders, use rainwater if your tap water is hard or softened. Remove damaged leaves only once healthy new growth appears.
Why Your Oleander Isn’t Blooming
Oleanders need full sun to bloom properly.32Gardening Know How. No Flowers On Oleander: What To Do When Oleander Will Not Bloom As neighboring trees and shrubs grow, they can gradually shade an oleander that once bloomed well.33Gardening Know How. No Flowers On Oleander: What To Do When Oleander Will Not Bloom
Pruning matters too, because oleander flowers form on new growth.34Garden Guides. My Oleander Is Not Blooming When pruning, leave enough new growth for buds to develop.35Garden Guides. My Oleander Is Not Blooming Hedges trimmed too often may have very few or no flowers,36Gardening Know How. No Flowers On Oleander: What To Do When Oleander Will Not Bloom and a common recommendation is to prune once a year, in fall.37Gardening Know How. No Flowers On Oleander: What To Do When Oleander Will Not Bloom To shape a hedge without losing blooms, cut whole older stems at the base instead of shearing all the tips. Shear only lightly, and only once a year.
Vigorous growth can come at the expense of flowers.38Houston Chronicle. How to make oleanders bloom Regular watering plus fertilizer produces dark green leaves and lots of soft new growth that isn’t mature enough to flower.39Xtremehorticulture of the Desert. Why Oleander Not Flowering Once that growth matures, the plant can bloom heavily.40Xtremehorticulture of the Desert. Why Oleander Not Flowering
If yours isn’t blooming, count the sunny hours; under about six a day is often too little. Think back to when you last pruned and how hard. Cut back high-nitrogen lawn fertilizer that spreads to the shrub’s roots. Then give the plant a season of steady care before expecting change.
Keeping a Potted Oleander Healthy
An oleander’s size is limited by its pot; in pots they reach roughly 1 m (3 ft) tall and 60 cm (2 ft) wide.41BBC Gardeners World Magazine. How to grow and care for oleanders Oleanders develop extensive roots, so watch for roots circling the pot and repot with better mix when they do.42National Gardening Association. Potted Oleander issues Repot every spring into the next pot size, or if the pot is already large, replace the top 3 to 5 cm (1 to 2 in) of soil with fresh potting compost.43BBC Gardeners World Magazine. How to grow and care for oleanders Occasional trimming encourages side shoots and flowers and reduces how much root space the plant needs.44MyGardenLife. Oleander Indoors (Nerium oleander)
Oleanders are frost tender, so in cold areas grow them in pots you can move under cover for winter.45BBC Gardeners World Magazine. How to grow and care for oleanders Potted oleanders often drop some leaves in winter because of lower light, which is normal and not a sign of disease.46National Gardening Association. Potted Oleander issues Indoors in winter, water less until growth picks up in spring.47MyGardenLife. Oleander Indoors (Nerium oleander)
Bring the pot in before the first frost, to the brightest spot available. Check for aphids and scale before it goes near your houseplants. In spring, move it back outdoors gradually, since sudden sun can scorch the leaves.
Handling Oleander Safely
All parts of oleander contain heart-affecting compounds called cardiac glycosides.48PubMed. Investigation of cardiac glycosides from oleander in a human induced pluripotent stem cells derived cardiomyocyte model If swallowed they can cause severe heart rhythm problems and death.49PubMed. Investigation of cardiac glycosides from oleander in a human induced pluripotent stem cells derived cardiomyocyte model They also upset the body’s potassium balance, which needs urgent hospital treatment.50PubMed Central. Human Deaths Related to Oleander Poisoning: A Review of the Literature Exposure can happen through swallowing, breathing it in, or contact with skin or eyes.51Elsevier. The world’s most toxic plants service personnel should be wary about
When pruning or cleaning up, wear gloves and long sleeves, and keep sap away from your eyes. Wash your hands and tools afterward. Never burn clippings, because the smoke can carry the toxins. Bag clippings so pets and livestock can’t chew them, and don’t use them as mulch.
Dogs can be poisoned by eating oleander. With fast, aggressive veterinary care, though, a poisoned dog can make a full recovery, in one case going home after 48 hours.52PubMed Central. Hypoglycemia associated with oleander toxicity in a dog Get a pet that chewed oleander to a vet right away rather than waiting for symptoms.
If a person swallows any, call poison control or emergency services immediately, even without symptoms. Bring a piece of the plant so staff know what was eaten. Watch for vomiting, a slow or irregular heartbeat, and dizziness.