Yellow leaves are often observed in tropical hibiscus, a shrub that you can grow outdoors year-round in a warm climate, or in large containers as patio or deck plants in colder climates. Tropical hibiscus is native to Asia and different from hardy hibiscus.
While yellowing leaves on a hibiscus plant are a common problem, in most cases it's manageable if you find the cause early and take prompt action.
Here are seven reasons why the leaves of your tropical hibiscus are turning yellow.
If some leaves on your hibiscus turn yellow and drop, the reason might simply be the plant is entering winter dormancy. Hibiscus grows during spring, summer, and fall; in winter, it stops growing for a while but remains evergreen. By the time the plant enters dormancy, container-grown hibiscus in cold climates should have been brought indoors for overwintering.
A few yellowing leaves in fall are no reason to worry, unless all of the leaves yellow and drop and the plant becomes defoliated, which indicates a different problem.
Insufficient light can cause discoloration and loss of leaves. In southern climates, your hibiscus might be fine in partial shade but in northern climates, it needs full sun during the growing season. Container plants should be moved to a location where their sun requirements are met. For in-ground plants, you can transplant to a suitable spot or prune surrounding vegetation to give the shrub more sunlight.
Too much sunlight, can also lead to leaf damage, especially in container grown hibiscus that has overwintered indoors. These plants often develop yellow leaves when they are moved back outdoors in the spring, a sign of too much light. The way to minimize this stress is to gradually adapt the plant to stronger outdoor sunlight. Start this process indoors by placing the plant near a bright, sunny window in early spring. Once you move it outdoors, gradually increase the amount of sunlight it receives, starting with a just few hours of direct sunlight. If your container plant is too large to move around easily, put it in its summer spot and protect it with an umbrella or a shade cloth.
Yellow leaves can be a sign of insufficient or the wrong type of fertilizer. Hibisci are heavy feeders that need a balanced fertilizer with equal amounts of nitrogen, potassium, and phosphorus, such as a 20-20-20 or 10-10-10 fertilizer. Potted hibiscus should be fertilized more frequently than in-ground plants, every two to three weeks during the summer but at half the strength recommended on the label.
Iron chlorosis is a particular form of micronutrient deficiency where only the leaves at the tip of each branch turn yellow and the veins remain green, with lower leaves initially remaining green. Feed the plant chelated iron in addition to the usual balanced fertilizer, at the dosage recommended on the label, to restore the natural green leaf color.
Both overwatering and underwatering can cause the leaves to turn yellow.
Tropical hibiscus needs a lot of water, even more so in hot weather and windy locations. Container grown hibisci are especially thirsty. The soil should be consistently moist. Under drought stress, the leaves turn yellow and drop, so never let the soil dry out completely. Check the moisture level at least every two days; if the top two inches feel dry, it’s time to water slowly and deeply until the soil feels slightly moist, not wet.
In-ground hibisci are less prone to drying out, and you can conserve soil moisture by applying a generous layer of mulch around the base. You should still keep an eye on the shrub and water it regularly and deeply in the absence of rain.
Too much water can also cause the leaves to turn yellow. When the plant gets more water than the roots can absorb, the soil remains soggy and the roots rot, which can happen both to container and in-ground plants. Check the drainage holes of your container to make sure they are large and not clogged. If your hibiscus is planted in heavy, dense garden soil, improve the drainage by adding organic matter.
Remember to water indoor hibiscus only moderately during the plant’s dormancy period. Again, checking the soil moisture is the best indicator to assess the watering needs.
Tropical hibiscus is not frost-hardy; its leaves will turn yellow and drop if temperatures are too cold. If you are located below USDA zone 9, bring the container indoors before the first fall frost, and do not move it back outdoors in spring until all danger of frost has passed.
Wind and Draft
This tropical plant does not like strong wind, which parches its leaves and can cause yellowing and leaf drop. Plant hibiscus where it is sheltered from wind. Container plants also need protection from hot summer winds.
Indoors drafts can have the same effect as wind outdoors so place the plant in a spot where there are no strong drafts during overwintering.
Spider mites, scale insects, mealybug, and hibiscus aphids are also a potential cause for yellowing leaves. Most of these pests are very small and difficult to detect. Outdoors, spraying the entire plant forcefully with water often gets rid of the pest. If the infestation is severe, you can also treat the plant with insecticidal soap or neem oil.
Hibiscus. University of Minnesota Extension.