Yellow is an excellent color for bananas and rubber duckies, but it’s not one you want to see on your plant’s leaves. The first sight of a bright lemony gold hue on hibiscus can cause even the most experienced gardener to catch their breath and worry.
Chances are that your leaves are changing colors for one of the following nine reasons.
What are the Main Causes of Yellowing Hibiscus Leaves?
While yellow variegation on leaves can be good with some plants, the plant is trying to tell you something if your hibiscus is developing yellow leaves. It’s signaling a specific need that has to be addressed. Familiarize yourself with the leading causes of yellowing hibiscus leaves so you can fix problems before they become severe.
Drought Stress Causing Leaves to Yellow
Hibiscus plants are native to tropical, rainy climates, so they prefer the soil to be consistently moist. When they experience a lack of water—drought stress—the leaves will become shriveled, yellowed, and curl downwards. The leaves may become dry, brown, and brittle in extreme drought stress, falling off the plant.
Drought stress is typically caused by not watering your plants often enough. As soon as the top of the soil starts to dry, they need another drink. But it can also be triggered when planted in sandy or rocky soils that drain quickly or when excessive winds pull water from the leaves.
Over-Watering is a Common Culprit for Yellowing Leaves
Behind underwatering, over-watering is another common reason you’ll see yellow leaves on your plant(s). Plants appreciate moist soils, but if you continuously saturate the ground, it creates boggy conditions that deprive the roots of oxygen. After a while, this lack of oxygen causes the roots to suffocate and the leaves to yellow.
Unlike underwatering, when plants are overwatered, the leaves will droop and may appear mushy instead of taking on a shriveled appearance.
Over-watering is usually linked to being given too much water too often but can also be related to slow-draining soils. Soils high in clay or heavily compacted drain too slowly for hibiscus plants. Water accumulates around the roots instead of moving down through the soil profile.
Nutrient Deficiencies in the Soil Cause Leaves to Turn Yellow
Regardless of your plant type, a common cause of yellowing leaves is a nutrient deficiency. Plants need certain “essential” nutrients to grow and thrive. They’ll exhibit deficiency symptoms when they don’t have enough of these nutrients. In the case of hibiscus, too little nitrogen, iron, manganese, or zinc shows up as yellow leaves that remain on the plant.
Nutrient deficiencies occur because the soil has naturally low fertility (e.g., sandy soils don’t retain nutrients as silt or clays do), overwatering pushes nutrients out of the root zone, or soil chemistry makes them unavailable for plant uptake. It can be hard to determine which nutrient is deficient since many symptoms look similar, but a key indicator is if the yellowing occurs on older or new leaves.
Adding organic materials to the soil is a great way to increase fertility and help hold on to nutrients naturally. If you opt to add conventional fertilizers, give them a half dose every couple of weeks from when plants start growing in the spring until flowers fade for the season.
Too Much Phosphorus Can Make Hibiscus Leaves Yellow
Nutrient toxicity can also cause the yellowing of your hibiscus leaves. Which only helps to make the problem harder to troubleshoot. Hibiscus are more sensitive to high levels of soil phosphorus than other plants. However, it isn’t the phosphorus (P) itself that causes problems—soil phosphorus accumulation ultimately causes other nutrients to become deficient and, in turn, the yellowing.
When phosphorous levels are too high, hibiscus plants naturally take in more of this nutrient than others, especially iron and zinc, even if they are present in adequate amounts.
Too much soil P is usually due to over-fertilization, mainly by applying products marketed as bloom boosters with higher phosphorus levels. If you think this is the cause of your yellowing leaves, scale back on fertilizer use for a while and keep watering the plant regularly.
Soil pH Affects Nutrient Availability and Triggers Yellowing
The pH of your garden soil is highly linked to nutrient availability. When soils are too acidic or too alkaline, it affects the nutrients available for uptake by the roots, and deficiencies occur. As discussed above, nitrogen, iron, zinc, and sulfur deficiencies trigger leaves to turn yellow.
Ideally, you want slightly acidic soil for hibiscus, with pH levels between 6 and 7 for optimal nutrient availability. Different factors like the soil’s parent material and rainfall amounts can impact soil pH, but You can amend the values if they are wildly out of range.
Not Enough Sunlight Can Make Leaves Yellow
If your plant is starved for sunshine, you’ll see its beautiful green leaves begin to yellow. Hibiscus plants need at least eight hours of sun daily. Photosynthesis slows when light levels are low and less glucose is formed. With less energy stored in the cells for other processes, plants synthesize less chlorophyll, and the leaves lose their green color.
Is Your Plant Preparing for Dormancy?
Keep in mind that hibiscus naturally grows in the spring, summer, and fall, going dormant for the winter. As autumn progresses, your plant might naturally start preparing for winter dormancy. It takes cues from shortening daylengths and dropping temperatures. You’ll see leaves begin to yellow, and they may even fall from the plant.
Unexpected Cold Weather Brings on Yellow Leaves
Another reason for yellow leaves on a hibiscus plant is an unexpected, abnormal drop in temperature. Tropical varieties are susceptible to cold and only grow in zones 9 to 11. Hardy types can tolerate colder weather but are still vulnerable to cold shock. In both types, chlorophyll breaks down, or synthesis halts if temperatures drop too low.
Are Insect Pests the Cause of Yellowing?
Hibiscus are known for being reasonably pest-resistant, but they are susceptible to infestations of spider mites. When they feed on the plant’s leaves, they pierce the cuticle and suck the nutrient-rich sap, causing yellow spots. Severe infestations cause the yellow dots to combine into a large mass, so the entire leaf looks yellow.
Special Considerations with Container-Grown Plants
If you are growing your plants in pots, you can see yellowing leaves for many of the same reasons. But container-grown plants are their own unique environment and create specific conditions. So it would help if you consider special factors that may be contributing to the problem.
- Lack of drainage in the pot is the most common cause of potted hibiscus developing yellow leaves. The yellowing is due to an abundance of water, similar to overwatering above. Too much water is usually attributed to inadequate drainage, whether the container doesn’t have drainage holes or the holes are blocked by roots when a plant becomes root bound.
- The growing mediums used in containers have much lower fertility than soils, and they can become depleted of nutrients over time. This depletion occurs as the plants use up the limited nutrients in the potting soil, and as water moves through the soil and out the drainage holes, it flushes nutrients to create a deficiency.
- Transplant shock is another common reason for yellow leaves in container-grown hibiscus. Hibiscus plants don’t like to be moved once acclimated to the sunlight and temperature of a location. Moving plants causes them internal stress, and the leaves turn yellow in response.