Unlike humans, plants don’t have an easy way to tell us gardeners that they are stressed.
We have to watch carefully for the signs, and one of the most obvious indicators your hibiscus (Hibiscus spp.) shrub isn’t happy is yellow leaves.
If you see yellow leaves on your hibiscus plant, it’s definitely trying to tell you that something is wrong.
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Identifying this particular stress sign is easy, the hard part is narrowing down the cause.
In this guide, we’ll chat about 11 common causes of yellow hibiscus leaves and how to figure out which one is causing the problem so you can get to work fixing it.
Here’s what we’ll cover:
Why Hibiscus Leaves Turn Yellow
Many causes of yellow leaves on hibiscus are environmental, meaning issues like over- or underwatering, lack of nutrients in the soil, temperature, or sun exposure.
The good news is that most of these can be resolved.
In this guide, we’ll discuss tropical hibiscus (H. rosa-sinensis) as well as hardy hibiscus (H. moscheutos), and the lovely rose of Sharon (H. syriacus).
Let’s talk about what temperature can do to our plants.
1. Cold Exposure
One of the first signs of cold damage is yellowing leaves. Tropical hibiscus (H. rosa-sinensis) is happiest in temperatures above 55°F, though there are cultivars that can tolerate temperatures a bit lower.
If the air temperatures dip into the 30s, your shrub could die.
Hardy (H. moscheutos) and rose of Sharon (H. syriacus) are both more tolerant of cold than tropical types. They can survive temperatures down to 20°F and -10°F respectively.
Cold damage on hibiscus looks similar to heat stress, with the foliage on the outer section of the shrub turning yellow. Eventually all the foliage will succumb.
It starts to get chilly, bring your tropical hibiscus indoors to overwinter.
If you are on the border of the right climate for the species you are growing, you can often get away with growing the plant against a southern-facing brick wall.
But don’t try to grow a tropical hibiscus if you aren’t in the right climate. It will only lead to heartache.
2. Heat Stress
Depending on the species or cultivar, some types of hibiscus can tolerate heat up to around 100°F without suffering.
But others will become stressed when the mercury rises above 85°F. Heat stress can cause the foliage to turn pale, either in patches or across the entire leaf.
Typically, it will be the outer leaves that turn yellow, while the inner leaves remain green. That’s because the leaves on the inside are kept cooler thanks to the protection from the outer leaves.
Generally, the edges of the leaves will turn yellow first, followed by the rest of the leaf. The leaves will eventually turn brown and die.
Hibiscus plants are heat lovers, so this isn’t usually a problem unless they also dry out during the heatwave.
There isn’t much you can do after it happens, but if you know there are high temperatures on the horizon, provide your plant with extra water and maybe even shade it with a big patio umbrella or some shade cloth, particularly during the hottest part of the day
3. Herbicide Drift
Sometimes when we – or a neighbor – sprays weeds or other unwanted plants the herbicide can travel to nearby plants and cause damage.
One of the easiest ways to be sure this is the problem is to inspect other species near your hibiscus for signs of distress.
Diseases rarely attack plants in different genera, so if your crape myrtle and your hibiscus both show similarly yellow leaves, it’s a good sign that the problem isn’t caused by a disease.
Remove the yellow leaves and your shrub should grow back in time. Avoid using toxic weed killers in your yard wherever possible, and always make sure you don’t spray on windy days to reduce the chances of drift.
4. Lack of Nutrients
A plant that doesn’t have enough nutrients will often exhibit yellow leaves. Usually, the veins will remain green but the plant tissue in between the veins turns pale.
But before you fertilize your hibiscus, you should test your soil.
For some plants, you can get away with skipping this step, but hibiscus is very sensitive to over- or underfeeding and getting it wrong can harm or even kill your plant.
Hibiscus plants generally need a lot of potassium. As one of the three major macronutrients, all plants need potassium, but hibiscus requires more than many other species.
Potassium is essential for photosynthesis, playing a critical role in growth and flowering.
When a hibiscus plant lacks potassium, it will exhibit stunted growth, wilting, and the leaves might become pale.
Phosphorus is also required for growth and development, but these plants are sensitive to phosphorus and too much will kill them, as we’ll discuss below.
If you decide to use a home test kit to check your soil, be sure to read the reviews before purchasing. Look for reviewers who have compared their results to those from a university extension office testing service.
I like to use MySoil test kit and the results I’ve had line up with those from my local extension office.
MySoil gives you a detailed analysis along with recommendations to help you bring your soil up to snuff.
MySoil Test Kits
You can find MySoil test kits available via Amazon.
Alternatively, contact your local extension office and send your soil sample to them for analysis.
After you’ve tested your soil and received the results, amend it accordingly. For example, if your soil is deficient in nitrogen but has adequate levels of the other macronutrients, you’ll want to work in some blood meal.
That’s what I have to do every year, since my soil is devoid of nitrogen but high in potassium and phosphorus.
Blood Meal
Blood meal is available at Arbico Organics in eight-ounce, four-, 20-, or 50-pound containers.
If your soil test shows that your sample lacks potassium, you can amend with kelp meal, which you can also purchase from Arbico Organics.
Kelp Meal
If the results reveal that it is significantly lacking in phosphorus you can add bone meal.
And if it’s deficient in all three macronutrients, purchase a balanced fertilizer with an equal ratio of nitrogen, phosphorus, and potassium.
This will be listed on the packaging as 10-10-10 or 5-5-5 (NPK) for example.
NPK are the letters that represent the three major macronutrients that all plants need: nitrogen (N), phosphorus (P), and potassium (K).
If you haven’t tested your soil, and you’re suspicious that the yellowing foliage is caused by a lack of nutrients, I’d advise you to pick a product with moderate nitrogen, little phosphorus, and a high amount of potassium.
A ratio of 15-5-25 or similar would be ideal. You can also find hibiscus-specific fertilizers with the right formulation available for purchase.
Espoma Palm-Tone is specifically formulated for palm trees and hibiscus plants. It has an NPK ratio of 4-1-5. Apply according to the manufacturer’s directions during the growing season.
Espoma Palm-Tone
You can find Espoma Palm-Tone available in four-pound bags via Amazon.
5. Not Enough Sun
I thrive in sunlight and emerge from the darkness of winter looking a little pale and wan. Hibiscus plants seem to feel the same.
They, too, will look a little pale and sad if they don’t receive enough sunlight. If lack of sunlight is the cause, the leaves will appear very light yellow and the plant probably won’t flower.
The solution, of course, is to provide more light.
You may have planted your hibiscus in a spot that receives plenty of light, so you might assume this isn’t the problem. On a sunny day, check your plant hourly over the course of the day and see how much light it is actually exposed. Or you can use a light meter.
Maybe a tree has matured in a neighbor’s yard or you planted it in the spring but the sunlight is all different in the late summer.
Your hibiscus needs at least six hours of light per day and if it isn’t receiving this, the plant needs to be moved, or you need to prune nearby trees and shrubs to increase the light exposure, if that’s possible.
6. Overwatering
Watering issues, whether over- or underwatering, are probably the most common cause of yellow leaves in most plant species.
In the case of overwatering, the roots are essentially drowning in too much water, and can’t access the oxygen they need to survive. Instead of going blue in the face, like a human without oxygen, the leaves turn yellow.
How can you tell the difference between overwatering and underwatering? If the problem is overwatering, the leaves tend to be soft and mushy, as well as discolored. They might have brown patches, too.
Check the soil, if it feels wet, it’s highly likely that your plant was overwatered or the soil isn’t draining sufficiently.
Even if the surface of the soil feels dry, dig down next to the roots and examine them. If you see soggy patches or discover that the roots are black or mushy, or there is a bad smell, it’s highly likely your plant is drowning.
If this is the case, and you haven’t been over-irrigating you’ll need to transplant your hibiscus into an area where the soil has better drainage.
7. Too Much Phosphorus
If you haven’t tested your soil, as we discussed above, and you have been adding an all-purpose, balanced fertilizer, there’s a good chance you could be overfeeding your hibiscus.
This is especially true if you’re using a “bloom booster” or other fertilizer formulated to promote flowering.
These plants don’t tolerate an overabundance of phosphorus as it interferes with their ability to absorb other minerals and nutrients from the soil.
Excess phosphorus causes stunted growth and the foliage takes on a sickly yellow hue.
If you examine the leaves, you’ll see that the yellow coloration appears between the veins, but the veins themselves remain green.
8. Too Much Sun
It’s pretty hard to give a hibiscus too much sun, but it’s possible.
Bright, direct sunlight, especially during the hottest part of the year, can lead to sunburn on the foliage. Typically, this will only appear as yellow patches or as white blotches on the leaves.
These leaves won’t fall from the plant, which is the main difference between this issue and some of the other causes on this list.
You can trim off the ugliest bits and provide some shade during the hottest, sunniest parts of the day.
If this becomes a recurring problem and providing shade is not an option, you either have to learn to live with the yellow leaves or move the plant to a more suitable location.
9. Underwatering
Without enough water, the plant becomes stressed and dries out, causing it to droop and wilt.
When this happens repeatedly, the plant will start to shed leaves because there’s simply not enough water in the tissues to move the nutrients absorbed by the roots to the foliage.
When a plant sheds its leaves as a result of underwatering, they will first turn dry and yellow, usually after wilting. You might also see dry, brown patches on the tips of the leaves.
Forgetting to water once in a while won’t cause immediate yellowing. This is more of an ongoing problem caused by a consistent lack of moisture.
Hibiscus likes a lot of water, especially during hot weather. If the ground feels dry, it’s watering time. Get out there and soak the soil and then keep an eye on the plant to ensure that you’re adding water whenever the top inch of soil dries out.
Hibiscus plants are also sensitive to drying winds as this strips moisture out of the foliage leading to a greater need for adequate water in the soil.
When this is the cause, it will look similar to underwatering, only you might see a majority of the symptoms on one side of the plant where the wind is strongest.
If your plant is in an exposed area and you have a lot of wind in the forecast, especially when the weather is hot, be sure to give it some extra water.
10. Verticillium Wilt
When I’m chatting with my fellow gardeners, few things will cause a record-scratch stop in the conversation than the words “verticillium wilt.” It makes me shudder just to think of it.
This disease is caused by soilborne fungi in the Verticillium genus and it is, to put it nicely, bad news. I’d take a major spider mite infestation any day over this disease.
The first symptom you’ll usually notice when a plant is infected is some of the leaves turning yellow. This usually happens on just a few branches at first and it might seem random.
Then part or all of the shrub will wilt and some of the branches will die. At some point, the entire plant will die, but it could take months or even years.
Because the symptoms are a little vague, you can confirm verticillium wilt by cutting off a symptomatic branch. Look at the cross-section. If you see dark discoloration, you can be confident of your diagnosis.
In the short term, you can prune out wilting or yellowing branches and keep your plant healthy with appropriate watering and feeding.
There is no cure, so all you can do is support the plant for as long as it lives.
Since the pathogen lives in the soil, it’s already in your garden, so removing the infected specimen won’t have any effect. If you do decide to pull up and dispose of the plant, don’t grow another species in the same area that is susceptible to verticillium wilt.
11. Wrong Soil pH
If your soil has the wrong pH for growing hibiscus, it will be difficult for the plant to absorb the nutrients it needs.
You could add all the fertilizer in the world, but the roots won’t be able to access it if the soil is outside of the optimal pH range.
So while this cause is similar to a lack of nutrients in the soil, it has a different cause. In addition to affecting absorption, the wrong soil pH can cause some micronutrients to become toxic.
Hibiscus plants are pretty adaptable, preferring a pH of about 6.0 to 6.5 but they will tolerate anything between 5.5 and 7.5 without suffering any negative consequences.
However, if your soil is outside of this range, the shrub will show the same symptoms as you would find with lack of nutrients.
Let the Flowers Be Yellow, Not the Leaves
Hibiscus shine when they’re in bloom. Their flowers are so bright and bold and they are unmistakable.
What about when they’re not in bloom? The foliage can also be beautiful, but not when it’s sickly yellow.
What kind of hibiscus are you growing? Are you still struggling to figure out the problem? Let us know in the comments section below and maybe we can help!
And now you might be interested in learning more about growing hibiscus in your garden. Check out these guides next:
