During my 1st winter caring for them, all of a sudden leaves started dropping. So, I had to ask the question: why are my bougainvillea leaves turning yellow and falling off?
Let’s be honest here, bougainvillea is not a plant I grew up with in the Connecticut countryside. I thought it was some kind of exotic plant until I moved to Santa Barbara 16 years ago where it’s found growing in some form or color on every block.
Bougainvillea is ubiquitous in warm climates I tell you. Yet in my opinion, it’s a beautiful “weed”. I had no experience growing bougainvillea until a bought a house 16 years ago with 3 of them on the property.
Turns out, this is one of the most common questions asked about bougainvillea. I’m sharing what I’ve learned (so far!) about this plant that can be used in many ways and gets covered with masses of beautiful flowers.
Note: This post was originally published on 3/16/2016. It was updated on 10/20/2022 to give more information.
Barbara Karst bougainvillea plants are prized for their prolific magenta blooms that add vibrant tropical flair to gardens. However they are susceptible to fungal and bacterial blights that can rapidly damage leaves and impair the plant’s health. Telltale dark spots on leaves are the first sign of blight. Swift action is required to treat blight and restore the beauty of your Barbara Karst bougainvillea.
What Causes Blight on Bougainvilleas?
Blight is caused by two common pathogens – the fungus Cercospora and the bacterium Xanthomonas. Both infect plants through wounds and openings, spreading quickly in warm, wet conditions. They produce lesions on leaves that expand, killing leaf tissue. Left unchecked, blight can defoliate the entire plant.
Recognizing Blight Symptoms
Watch for these early signs of blight on your bougainvillea’s leaves:
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Small dark spots that rapidly expand into larger lesions
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Angular, yellowed areas around lesions that eventually turn brown
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Leaf drop starting with infected leaves then spreading
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Twig dieback when infections reach stems
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Stunted growth and lackluster blooms as blight progresses
Effective Treatment Methods
At the first sign of blight, take action to contain infections and restore plant health. Useful treatment methods include:
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Prune infected parts – Remove affected leaves, stems, and spent blooms, pruning 6-12″ below visible symptoms. Sterilize tools between cuts.
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Improve airflow – Space plants to allow air circulation and thin inner branches. This reduces humidity.
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Apply copper fungicide – Copper-based products combat blight-causing pathogens. Spray every 7-14 days.
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Use organic alternatives – Options like neem oil, compost tea, and baking soda also deter fungal/bacterial growth.
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Water wisely – Avoid overhead watering and irrigate at soil level. Allow soil to dry between waterings.
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Boost overall health – Fertilize regularly and properly to strengthen the plant’s defenses.
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Remove plant debris – Clear fallen leaves and blooms to eliminate sources of reinfection.
Tips for Prevention
While dealing with active blight is vital, prevention is ideal to avoid infections in the first place:
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Select resistant bougainvillea varieties like Barbara Karst
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Allow for adequate airflow and direct sun exposure
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Give plants proper spacing at time of planting
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Water early in the day so leaves dry fully
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Disinfect gardening tools after use on infected plants
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Apply copper spray proactively before symptoms appear
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Avoid overhead watering which spreads blight spores
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Monitor frequently and remove diseased parts promptly
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Clean up and dispose of leaf litter and fallen blooms
Why Act Fast to Treat Blight?
Blight spreads rapidly, so early intervention is key. Left unchecked, it can quickly defoliate and kill susceptible bougainvilleas. Barbara Karst bougainvilleas have good blight resistance but are still vulnerable under the right conditions. Treating blight at first onset contains damage and protects the plant’s health and form. Don’t delay treatment once those telltale leaf spots appear!
How to Safely Prune Diseased Areas
Pruning away infected parts is crucial for blight treatment. Follow these guidelines to prune safely and effectively:
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Sterilize pruning tools in a 10% bleach solution between each cut.
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Prune at least 6-12 inches below visible lesions to remove hidden infections.
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Prune into healthy wood and dispose of pruned material promptly.
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Avoid pruning in cool, wet weather which encourages blight spread.
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Prune on sunny days ideally in the morning hours.
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Wear gloves and long sleeves to protect your skin when pruning diseased plants.
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Inspect the plant thoroughly and remove any remaining affected areas.
Timing Copper Sprays for Maximum Effectiveness
Copper is most effective when sprayed before symptoms arise as a protective barrier. For treatment, proper timing is also key:
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Spray early morning or late evening to avoid leaf burn.
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Allow 12-24 hours of drying time before rain or irrigation.
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Repeat application every 7-14 days for 2-3 cycles.
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Spray both sides of leaves thoroughly for full coverage.
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Reapply after new growth emerges or heavy rainfall.
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Avoid spraying during temperature extremes or in direct sun.
Organic Alternatives to Copper Fungicides
If you wish to avoid synthetic fungicides, consider these organic treatment options:
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Neem oil – Contains antifungal azadirachtin. Suffocates spores and inhibits growth.
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Baking soda – Creates an alkaline environment to deter fungal propagation.
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Compost tea – Boosts beneficial microbes that protect against infection.
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Milk spray – Coats leaves with lactobacillus to suppress fungal growth.
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Hydrogen peroxide – Oxidizing effect kills fungal spores on contact.
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Sulfur powder – Prevents spore germination. Use wettable powder formulations.
Providing Good Growing Conditions
While dealing with blight, don’t neglect general care for your bougainvillea. Providing optimal growing conditions encourages vigorous regrowth after pruning.
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Ensure plants get at least 6 hours of direct sunlight.
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Allow room for air circulation between branches.
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Water deeply 1-2 times per week, avoiding wet foliage.
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Apply balanced fertilizer every 4-6 weeks during growth.
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Keep soil evenly moist but not waterlogged.
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Monitor for pests like aphids that can further weaken plants.
Be Diligent About Prevention
Even when blight subsides, remain vigilant about prevention to avoid repeated battles with this destructive disease. Employ these proactive measures in an ongoing blight prevention program:
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Inspect plants frequently and remove any suspicious spots.
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Disinfect tools regularly.
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Eliminate weeds, debris, and dead leaves.
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Allow space between plants for airflow.
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Prune judiciously to open up inner branches.
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Water early in the day, avoiding wet foliage.
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Apply preventive copper spray before rainy periods.
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Monitor environmental conditions and avoid overly wet conditions.
Staying one step ahead of blight is the best way to safeguard the health of your beloved Barbara Karst bougainvillea. A little diligence goes a long way!
Do All Bougainvilleas Drop Leaves?
It’s interesting because I’ve noticed that some Bougainvilleas drop more leaves than others. And, there are many different types of bougainvilleas not to mention bougainvillea varieties!
I’ve been told that some varieties tend to shed more than others do although I haven’t delved too far into that topic. However, I’ve observed that Bougainvilleas in cooler, shadier, windier, etc parts of town shed more leaves than those in more sheltered areas with direct sunlight.
There’s a huge hill behind my house that looks out over the ocean, blowing those cool winds. When I was taking a late winter walk up there, I noticed that a 2 block long hedge of bougainvilleas (I believe they were B. San Diego Red) had almost completely defoliated. But, once the weather warmed, they all started to leaf out like crazy.
What Causes Bougainvillea Leaves To Fall Off
My initial experience with the Bougainvillea leaf color change and drop issue had me scratching my head. What was I not doing? Or, was I doing something I shouldn’t be?
I did some reading and got some answers but the final confirmation of the cause came when I visited San Marcos Growers that February to pick up some plants for a client in the San Francisco Bay Area. They’re a large wholesale plant grower with an excellent reputation so, with ears open wide, I listened closely to what they had to say.
Here’s the scoop: Bougainvillea plants are tropical plants native to coastal areas. They do great in Santa Barbara where the winter temperatures rarely dip below the low 40s but the tropics it is not.
One of the causes for those heart-shaped leaves turning yellow (and yes, they turn completely yellow) is environmental. Those cold temperatures in the winter months will do it.
Once leaves turn yellow, then they’ll fall off. As I said above, green leaves will drop also. Some will hang on and then fall off in late winter/early spring when the new growth appears.
In both Santa Barbara and Tucson bougainvillea is semi-deciduous. Not all the leaves fall off but maybe 1/2 of them. Tucson has colder evening temps and I had one of my bougies hit fairly hard but the leaves hit by the freeze turned dark brown and hung on. You can see more on this below.
Water stress in general can cause this. Another reason why yellow leaves fall off of Bougainvilleas in winter is due to a prolonged dry spell. The last few winters haven’t been too cold but they have been dry. The lack of rainfall in the last 5 or 6 winters has brought on drought conditions so the bougies just aren’t getting the water they were used to.
Conversely, leaves can fall off bougainvilleas in the case of too much water. Established bougies prefer infrequent but deep waterings.
Transplant shock. If they’re happy, bougainvilleas are tough cookies and grow like crazy. Despite this fact, their root systems are very sensitive. I’ve never attempted to transplant a bougainvillea and it can be tricky business if you try it. When I plant bougainvillea, I always plant them in their grow pots. This is another tip I learned from another grower back way back when.
How to Grow Beautiful Barbara Karst Bougainvillea – Tips and Tricks for Success
FAQ
How do you treat bougainvillea blight?
What is the best fungicide for bougainvillea?
How can I bring my bougainvillea back to life?
How much water does Barbara karst bougainvillea need?
Barbara Karst Bougainvillea needs 0.8 cups of water every 9 days when it doesn’t get direct sunlight and is potted in a 5.0″ pot. Use our water calculator to personalize watering recommendations to your environment or download Greg for more advanced recommendations for all of your plants. Does your plant get direct sunlight?
Why does my Barbara karst bougainvillea lose its leaves?
There are times when my Barbara Karst Bougainvillea loses its leaves, particularly if it gets too cold. It’s a semi-deciduous plant, which means it can shed its leaves in response to stress, like a drop in temperature or insufficient water. However, once the conditions improve, it usually bounces back with new growth.
How do you care for Barbara karst bougainvillea?
Barbara Karst Bougainvillea is a fast growing plant and may deplete the nutrients in its soil over time. Replenish them with a gentle organic fertilizer or compost every 1-2 months depending on your location and season. Fertilize more often during the growing season and in warmer and brighter climates.
When to plant Barbara karst bougainvillea?
Choosing the Right Time and Location: The best time to plant your Barbara Karst Bougainvillea is in spring or early summer after the danger of frost has passed. Select a location that receives full sun, ideally at least 6-8 hours of direct sunlight daily. Bougainvillea thrives in warm temperatures. Ensure the planting site has well-draining soil.