Mandevilla plants are versatile growing well in pots, hanging baskets, trailing up and down your trellis, or growing along a wall. These trumpet-shaped flowers have glossy leaves that are a delight in anyone’s garden, but they can sometimes suffer with leaves that turn brown and then fall off of the plant.
It can be disheartening for this to happen, but once you know what causes these brown leaves and you know what to do about it, you won’t have to panic as much. Browning leaves on the mandevilla plant are usually caused by inconsistent watering, bacterial wilt, fungal attacks, or environmental stress.
This article will explore the top 4 causes of mandevilla leaves turning brown and falling off and how you can solve each one.
Why mandevilla leaves turn brown and fall off
Here are the most common causes of leaf problems on mandevilla plants.
1. Inconsistent Watering
Mandevilla plants are tropical and grow best in moist, nutrient rich well-draining soil. Plants that do not get enough nutrients or enough water can develop brown leaves that will eventually fall off.
Check the soil moisture by sticking your finger in 2 inches below the surface. If it feels dry then it is likely that your mandevilla is underwatered. Deep water the plant with your hose until you see water drain from the pot or until the whole root zone is damp.
Repeat this again when the soi surface dries below 2 inches. You can also stick a popsicle stick in the ground and if it comes out clean then the soil is too dry. Surround the plant with bark mulch to help to keep moisture in the soil for longer.
If the soil temperature is more than 85 degrees Fahrenheit, you’ll want to water the plant up to twice a day until the temperature cools. When the weather is hot and dry, test the moisture of your soil regularly.
Fertilize the plants with a water-soluble fertilizer once a month over their main growing season of spring and summer. This will help to avoid the plant drying out and stop the leaves from turning brown.
2. Bacterial Wilt
Bacterial wilt is a disease that sometimes happens when the temperature outside gets over 85 degrees Fahrenheit. Bacteria block the vascular tissues of the plant so that the water and nutrients you’re feeding it don’t always reach its leaves and stems.
This results in wilting leaves that turn yellow and eventually brown. This is a difficult disease to get rid of, but you can apply a specialized fungicide containing copper. Trim off the excess leaves affected by the wilt and water the plant well.
3. Fungal Diseases
Mandevilla plants can suffer from fungal diseases, with the main ones being Botrytis blight, fungal leaf spots, stem rot, and sooty mold. Botrytis blight usually occurs in cooler regions where the temperatures get under 41 degrees Fahrenheit.
Fungal leaf spots can be caused by a range of fungal species. They appear as brown spots on the leaves instead of solid brown leaves. Eventually, the leaves can curl then fall off the plant.
Stem rot will cause the vines of the mandevilla plant turn yellow and then brown, and all of the branches and twigs wilt.
Sooty mold is common when there is a lot of water around, high rainfall or if you water the plant directly on the leaves. A brown or black coating occurs on your leaves, and sometimes the mold even spreads to your branches as well.
To take care of this problem, you’ll need to remove and dispose of the infected leaves then use a fungicide on the plant. Make sure you find a fungicide that is appropriate for these flowering plants.
To help the plant to recover you can repot mandevillas in fresh potting soil after disinfecting the current pot, your equipment and garden tools.
To avoid this problem always water in the morning but do not sprinkle water directly on the leaves. Make sure the plants have plenty of space between them because if they’re too crowded, fungal infections are more likely.
4. Environmental Stress
Environmental stresses can directly affect the health of your mandevilla plants. Plants need around 6-7 hours of direct sunlight every day, they cannot be over-fertilized, and they do not like temperatures below 45 degrees Fahrenheit.
Any changes from these ideal conditions can cause the leaves to turn brown and fall off. Rapid changes in temperature, hot afternoon sun or extreme winds can stress the plant causing it to draw water from the leaves causing damage.
If this does occur you can take a pair of garden shears and trim off all of the brown parts of the leaves. You can repot the plant if you have used too much fertilizer, and you can start moving potted mandevillas to the shade once the hot afternoon sun arrives.
Avoid fertilizing mandevilla plants during the winter when the plants are dormant. Keep the plants indoors in the winter and outdoors in the summertime if you live in a cold climate.
None of these rules are difficult to remember, but they’re very important when you want mandevilla plants that are lush and healthy.
Conclusion
Mandevilla plants are beautiful and versatile. Whether you grow them in the ground or in a pot, they are susceptible to certain challenges that can turn the leaves brown and cause them to fall off at some point. Watering problems, bacterial wilt, fungal diseases, and certain types of environmental stress are all things that can happen to these plants to cause browning leaves, but now that you know what to look for and what to do about the problems, it should be a little easier to handle them.
All plants come with potential challenges, but if you’re growing mandevilla plants in areas that don’t get a lot of sun, it could create more problems than usual for them. These problems are easy to recognize when you know what to look for, and they’re even easier to solve if you know how.
I am an accredited practicing dietitian, experienced gardener and a dedicated cook. I love writing and sharing my experience so you can learn from my successes and mistakes.