Hibiscus flowers are some of the easiest to recognize due to their associations with tropical islands and Polynesian culture.
The hibiscus flower has bright, colorful petals that radiate warmth and sunshine. These plants even have a place in alternative medicine.
There are two main varieties of hibiscus plants: hardy and tropical. Among these types, you will find some species that can function as both annuals and perennial shrubs, and even some native to the United States.
Regardless of the variety, hibiscus leaves can lose their vibrancy when they turn yellow. In this article, I want to discuss the eight primary reasons for hibiscus leaves turning yellow and how to treat them.
Reasons For Hibiscus Leaves Turning Yellow
While hibiscus flowers are beautiful, they are readily distressed. When the leaves start turning yellow, it usually has to do with the plant’s stress levels. Some of the causes for yellowing leaves include:
- Drought stress
- Overwatering or poor pot drainage
- Nutrient deficiency
- Phosphorus accumulation
- Imbalanced soil pH
- Temperature shock
- Low light
- Pest infestation and disease
The yellowing of leaves is often due to a combination of several factors. Before we explore these reasons further, we will cover how you can revive your plant.
How Do You Revive a Hibiscus Plant?
When looking to revive your hibiscus plant, ensure that you have discovered the cause of the discoloration. Some of these steps might come in handy to remedy your dying hibiscus:
- Ensure that you have chosen a hibiscus variety that can grow in your climate
- Protect it from harsh winds
- Keep the soil’s moisture consistent and uniform throughout the pot
- Spray mist on the plant to simulate humidity
- Choose a soil with more organic matter
- Add a 2-inch layer of mulch
- Consider switching to a multipurpose compost instead of soil
- Apply fertilizer each spring, unless you notice phosphorus buildup
- Ensure water can flow from the pot’s base by removing the tray or saucer
- Place the hibiscus somewhere it can receive 5 hours of sunlight
If you live in a dry or windy region, your hibiscus might suffer from dry soil. The lack of humidity and harsh winds can make it difficult for the soil to retain sufficient moisture.
Even if you live in a tropical region, bringing your plant inside can expose it to air conditioning, fans, heating units, and dry conditions that may lead to hibiscus leaves turning yellow.
Drought stress can also occur from overexposure to the sun, especially when combined with dry conditions. These plants need around 5 to 6 hours of sunlight per day, and excessive amounts can lead to the leaves yellowing.
Both hardy and tropical hibiscus plants benefit from moist, fertilized soils. Regardless of your landscape or hibiscus type, you will likely need to water a potted plant more than one that is planted in the ground.
How To Revive Your Hibiscus
If the soil feels dry to the touch, you will need to simulate a humid micro-climate around the hibiscus. Spritzing the plant with water every day can increase humidity and prevent moisture loss.
Water the soil regularly to keep it consistently moist. The frequency with which you water will depend on your climate and soil type. Make sure to water whenever the soil feels dry but not to the point that it puddles around the plant.
A soil moisture meter can monitor the moisture levels in the pot to help you stay on top of your plant’s health. Some even send digital alerts to your phone to remind you to water your hibiscus.
If your hibiscus seems to dry out rapidly after watering, try using mulch. Water heavily and apply a 2-inch layer of mulch, straw, bark chips, or a ground cover companion to slow evaporation.
For those in windy regions, I recommend keeping your hibiscus in a sheltered area during times of high winds. If you keep it in a pot, you can move it to a fenced or enclosed spot that will protect it from the elements. Otherwise, consider bringing it inside (but keep it away from air conditioning or radiators).
Overwatering or Poor Drainage
All plants need sun, soil, and water. But too much of a good thing can lead to hibiscus leaves turning yellow. Both tropical and hardy hibiscus are susceptible to overwatering.
Consider your current watering schedule! Maybe you water your plants too often, have insufficient pot drainage, or need to improve the soil conditions.
Any of these factors can lead to root rot, which is detrimental to your hibiscus’ health.
Watering Hibiscus Too Often
Overwatering your hibiscus can create boggy conditions in the soil. These plants require uniform moisture throughout the soil.
If you water hibiscus plants daily, the soil can get overly damp around the roots. Excess moisture can prevent oxygen from penetrating the soil and have a detrimental effect on the health of your hibiscus.
Poor Pot Drainage
Pots and containers without drainage holes prevent excess water from escaping, which can cause water to pool around the roots, eventually leading to root rot.
Even containers with adequate drainage can cause root rot if left to sit in a collection saucer full of extra water. If you must use a saucer under your potted hibiscus, I recommend elevating the container an inch or so for proper drainage.
Furthermore, slow-draining soils might trap the water around the roots for too long, which also hinders root respiration.
Treating and Preventing Root Rot
If you can save the plant before the roots become slimy, you may revive it. However, it’s best to work toward reducing the risk of root rot from the start. Once root rot sets in, it becomes much more difficult to reverse the damage.
Rather than watering every day, get into the habit of checking the soil levels with your finger or a soil moisture meter.
Plant your hibiscus in a pot with drainage holes. If you keep it in a saucer, allow water to drain completely from the drainage holes before replacing the saucer.
Use soil that contains organic matter as well as gravel or grit to promote drainage and optimize moisture levels. Alternatively, plant in multipurpose compost rather than soil as this can also help with drainage and will add additional nutrients.
You could also try mixing the soil with sand and adding gravel to the bottom of the pot.
Sometimes, issues with the soil, water, and the environment lead to nutrient deficiencies in a hibiscus. Different deficiencies manifest in different ways. For example:
- Iron: The youngest leaves will grow smaller and turn yellow with green veins
- Magnesium: The lower leaves lose their shine and become yellow with green veins
- Nitrogen: The older leaves turn yellowish, including the veins
- Zinc: The younger leaves are closely-spaced, small, pale, and twisting
- Potassium: The lower leaves become brown at the tips and edges
- Molybdenum: Older and younger leaves become mottled; younger leaves become narrow, leathery, long, and twisted with parallel veins (strap leaf)
- Manganese: The younger leaves turn yellow-green with thick, dark green veins
The most important nutrients for plants are nitrogen, phosphorus, and potassium. These are found in different ratios in all fertilizer products.
Contrary to many other flowering plants that require large amounts of phosphorous to bloom, hibiscus cannot tolerate too much phosphorous.
Instead, they need a medium amount of nitrogen (N), a small amount of phosphorous (P), and a large amount of potassium (K).
Nitrogen supports healthy foliage and is used by plants to produce chlorophyll. For hibiscus fertilizing, always err on the side of caution with the amount you use, especially if your soil is already nutrient-rich and/or if you mulch regularly.
Overfeeding phosphorous to your hibiscus will prevent zinc and iron from being absorbed by the roots, which will inhibit flower production.
Hibiscus plants need potassium in abundance. It encourages robust root, stem, and leaf development and supports the process of photosynthesis. Potassium also provides resistance against pests and diseases.
How To Fertilize Your Hibiscus
The best time of year to start fertilization is early in the spring before the growing season. Then, you can continue fertilizing hibiscus every other week until the end of the season.
Applying slow-release granules and powder means you won’t have to fertilize as frequently compared to fast-acting liquid feeds that provide an instant boost of nutrients but will need to be applied more frequently due to the run-off that occurs.
The tropical hibiscus’ growing season lasts from early spring to late fall. They remain green year-round if cared for properly.
On the other hand, hardy hibiscus grow in the spring and go dormant in the winter. You only need to fertilize during the active growing season.
Phosphorus Accumulation in Soil
Phosphorus is an essential nutrient for energy storage, root formation, and seed production. Hibiscus plants need significantly less phosphorus when compared to many other varieties of flowering plants. However, this nutrient does not leach out of the soil and remains for long periods, which can lead to accumulation.
According to Texas A&M University, excess phosphorus can reduce the availability of minor elements like iron and zinc, especially if you have alkaline soil. It can take up to a year to lower phosphorus levels back to normal.
As I mentioned previously, iron and zinc deficiencies can cause the leaves of the hibiscus to turn yellow, grow smaller, and sometimes get twisted. Phosphorus accumulation can give the plant a drooping appearance and prevent hibiscus flowers from blooming.
Usually, phosphorus accumulation happens from applying too much phosphorous-heavy fertilizer.
How to Fix
Start by checking the NPK ratio of your fertilizer. If the phosphorus levels are more aligned with nitrogen and potassium, you should consider switching to a different fertilizer. Look for feeds containing blood meal or pine bark as these have low phosphorus levels.
Manure also tends to contain high phosphorus levels. When using organic matter, try mulching instead.
Reduce the frequency of fertilizing and water more regularly to ‘flush out the accumulation of salts.
Use a soil test kit to understand the breakdown of nutrients and to highlight any deficiencies.
Since phosphorus often strips the soil of iron and zinc, you might want to add these minerals directly to the soil using a sprayer.
Soil pH Too High or Too Low
Soil pH identifies the alkalinity or acidity of the soil. Hibiscus plants benefit from neutral to slightly acidic soil. The best soil pH for hibiscus plants is 6.0 to 7.0. Both tropical and hardy hibiscus plants require this pH level.
If the pH is too high, you have overly alkaline soil. Low pH levels indicate acidic soil. If the pH is off-balance, plants will struggle to absorb nutrients from the soil, which can lead to hibiscus leaves turning yellow.
How To Amend Soil pH
After performing a pH test, you will know if you need to add more bases or acids to the soil to create the ideal levels.
- pH Too Low: Add more alkaline materials, such as organic agricultural limestone
- pH Too High: Add acidic materials, such as agricultural sulfur or composted sawdust and woodchips
Perseverance is required as nutrient deficiencies in the soil cannot be corrected overnight. Continue to apply the soil amendments and test your soil weekly until you achieve a 6.0 to 7.0 pH.
Tropical hibiscus prefer full sunlight and heat. It cannot handle USDA hardiness zones below 9, and thrives in zones 10 to 12.
These plants are green year-round and often survive at least five growing seasons, although they need a consistently warm climate to thrive. For cooler winter climates, consider bringing your tropical hibiscus indoors to maintain warm temperatures and high humidity.
Hardy hibiscus plants can grow in full sun but can also tolerate partial shade. Some varieties require temperatures below freezing in winter to grow back in the spring. These hibiscus flowers thrive in zones 4 to 8.
Growing hibiscus outside of these climate zones can lead to temperature shock that will stunt growth, reduce or prevent hibiscus blooming, and may even kill the plant.
Low Light Conditions
Tropical hibiscus plants prefer bright conditions and need at least 6 hours of sun exposure daily. Whilst they can tolerate some full sun, they do need protection during the hottest part of the day to avoid scorching.
Hardy hibiscus plants can tolerate some degree of shade, however, placing them in a bright position will produce better growth.
Low light conditions can cause leaves to turn yellow and reduce the process of photosynthesis. Ultimately, this can significantly impact the health of the hibiscus and may even kill the plant.
If you bring your plant inside for any reason, put it near a sunny window that receives at least 5 hours of sunlight each day.
Does Hibiscus Need Full Sun?
Both tropical and hardy hibiscus enjoy bright conditions. However, too much exposure to full sun can scorch leaves and delicate petals, so avoid exposure during the hottest part of the day.
Low light conditions can reduce the vibrancy of the petals and lead to yellow leaves.
Pest Infestation or Disease
Aphids, mealybugs, mosquitoes, thrips, and white flies are all common pests that are partial to devouring hibiscus flowers or attacking leaves and stems.
Aside from blasting areas with a jet of water to remove clusters of an infestation, you can use horticultural oil, insecticidal soap, foliar sprays, or a systemic root drench to treat infested plants.
You could also consider using natural insect predators like dragonflies and ladybugs, to keep pest problems at bay.
Three common hibiscus diseases are leaf fungus (leaves with black spots), dieback disease (some wilted leaves), and wilt disease (yellow, wilted leaves).
You can mitigate these diseases by removing dead or infected flowers and leaves with sanitized pruning shears. You should also remove broken or diseased branches, as well as hose your hibiscus with water.
To specifically treat dieback disease, cut away the infected stems. Cut further back until the inner core of the stem is white and clean. Then, apply grafting wax to seal the cut.
For wilt disease:
- Take your hibiscus out of the sun
- Mist the leaves and stems
- Remove any dead or yellow leaves, but leave on any wilted yet green leaves
- Wait to water until the soil dries
I recommend quarantining potted hibiscus away from other plants to help avoid further infestation.
Solved: Hibiscus Leaves Turning Yellow
For most causes of yellow leaves, you can reverse any damage and revitalize your plant by keeping the soil evenly moist, applying a fertilizer that suits the pH levels of your soil, keeping the plant in full sun, allowing for drainage, and pruning your hibiscus regularly.
By taking care of your plant, you can prevent diseases and keep it looking its best. While you cannot add chlorophyll back to a leaf, you can ensure that new growth is healthy and results in large, green leaves.