The many varieties of hoya are some of the most popular houseplants in the world right now. They have beautifully-colored leaves and flowers that can inject life and vigor into any space they are in.
They are also low-maintenance and do not require that much attention to thrive in an indoor setting. That said, these plants do still have their share of problems to which they may be prone.
One of these problems is when the plant’s leaves turn yellow. If a hoya’s leaves turn yellow, it means there is an environmental factor causing the plant stress, which should be addressed immediately.
The possible causes of yellowing hoya leaves are incorrect watering, improper lighting, poor water quality, temperature changes, fertilizer problems, lack of nutrients, and pests.
In this article, we will discuss each of these causes and how they can be fixed.
If you are currently experiencing this problem and you wish to learn more, just keep on reading.
Why are my hoya’s leaves turning yellow?
1. Incorrect watering
Giving your hoya too much or too little water will result in the plant’s leaves turning yellow.
Hoyas are native to tropical places, so they are used to having access to water every couple of days and do not take well to drying out.
Underwatering can happen when the plant’s watering needs are neglected or if the plant is kept in a place where its soil dries out faster than it should. Not only does the plant need moisture from the water; plants also use water to transport minerals and nutrients from the soil into the roots. Without these minerals and nutrients, the plant will be unable to feed itself. This results in the yellowing, wilting, and drying of the leaves.
Overwatering is an even worse mistake to inflict on your plant because it has more permanent effects and can even lead to the plant’s death.
When the plant’s soil is constantly wet, the plant will keep absorbing water until the cells in its leaves and stems rupture from all the excess water. This will manifest as yellowing leaves.
Eventually, the leaves will become soft and mushy, which is a symptom of root rot.
Root rot is a condition caused by extended exposure of the roots to waterlogged soil. The roots will have no access to oxygen and will therefore drown and die. The dead roots will become susceptible to opportunistic pathogens in the soil, and these will help the rot spread more aggressively to the rest of the plant.
By the time the rot has reached the stems and the leaves, it is usually too late to save the plant and you might have to throw it away.
If you suspect that your hoya is underwatered, all you need to do is water it immediately. Soak all the soil in the pot with water and keep watering until excess water starts flowing out of the drainage holes at the bottom of the pot.
If, on the other hand, you think your hoya may be overwatered, stop watering it and let the soil dry out completely. If the overwatered plant’s leaves have started to become mushy near the base, it might have root rot and you will need to check the roots to be sure.
Remove the plant from its pot and wash off as much potting soil as you can without damaging the roots.
Inspect the roots closely, looking for sections that have turned brown or black. These roots are rotten and will have to be removed. Use a sterile pair of scissors to cut away the rotten roots until only healthy, white roots remain.
Then, lay the plant on a dry paper towel and let the roots air-dry for several hours.
Prepare a new pot that has drainage holes at the bottom and fill it two-thirds with fresh potting soil. Place the plant in the middle of the pot and cover the roots with more potting soil.
The best way to prevent both underwatering and overwatering is to know exactly when to water your plant. You will know that your hoya needs watering if the top two inches of soil are dry to the touch. If the top two inches of soil are still damp, wait one or two days before checking again.
2. Poor water quality
Another reason your hoya’s leaves are turning yellow could be that the water you are giving it is not ideal.
Tap water contains minerals that accumulate over time and turn into mineral salts in the soil, which can have adverse effects on the plant.
One of the signs of built-up mineral salts in the plant’s pot is the yellowing of its leaves and dark spots appearing on the plant.
These minerals can inhibit photosynthesis, which leads to the discoloration that you see. If the plant cannot photosynthesize, it cannot feed itself and will become stunted and possibly even die.
Refrain from using tap water on your plant because it might contain fluorine and chlorine.
If you have no other choice but tap water, place it in a container and let it stand for at least one day to let the chlorine evaporate from it.
If you have the means, install a filtration system that connects to your tap so that you can remove the minerals from the water.
Or, if you can, collect rainwater and use this to water your plant. You can also use melted snow.
Also, make sure that the water you give your plant is neither too hot nor too cold.
3. Temperature changes
Íf you place your hoya in a spot where the temperature is constantly changing and reaching extremes, this could lead to the yellowing of its leaves due to stress.
These plants like temperatures between 65 and 75 degrees Fahrenheit, and if the temperature around them drops below 65 degrees for long periods, this will cause them problems. If you are keeping your plant outdoors in the frost, ice crystals will form in the plant tissue and will disrupt photosynthesis.
Meanwhile, if the temperature around the plant is too high, the normal processes of the plant will cease to function, and the plant will sustain rapid water loss.
Either extreme temperature can also result in shallow root growth and reduced rooting.
To stop the yellowing of hoya leaves due to temperature changes, you just need to place the plant in a spot where the temperature is stable and is not constantly changing.
Your plant might do well on your windowsill during the warmer months, but you may need to transfer it in the winter because the drafts that pass through the cracks around your windows will dry the plant out.
Do not place the plant near a heater or a radiator, because these warm drafts will also dry out its leaves.
Ideally, place a thermometer in the room where you keep the plant so that you are always aware of the temperature, and transfer the plant if it becomes either too hot or too cold in the room.
4. Fertilizer problems
We fertilize our houseplants because we want to help them reach their full potential and to keep them happy.
Unfortunately, too much fertilizer can cause a build-up of excess minerals and nutrients in the soil, and this can cause root burn. A hoya with root burn can also exhibit yellowing leaves.
This is due to the changes in the soil’s pH which can affect the plant’s ability to absorb nutrients from the soil.
Too much fertilizer can also encourage plant growth with poor root structure.
In severe cases of overfertilization, the plant may even die.
If you think the cause of your hoya’s yellowing leaves is overfertilization, refrain from fertilizing the plant immediately and flush the soil in the pot. Do this using an amount of water five times the volume of the plant’s pot. Let the excess water flow out of the drainage holes at the bottom of the pot before returning the plant to its usual spot.
In order to prevent overfertilization, do not fertilize the plant during the cold months. This is because the plant is not actively growing during these months.
Fertilize only in the spring and summer, which is the plant’s active growing season.
5. Lack of nutrients
If your hoya is not getting the nutrients that it needs to function properly, this can also lead to yellowing leaves.
Hoyas need magnesium, potassium, and nitrogen to live, and if there are low levels of these nutrients in the soil, this causes stunted growth and even deformity of the leaves.
In order to fix a nutrient deficiency, you need to replace the nutrients your hoya is lacking.
This can be achieved by fertilizing it correctly, placing it where it can get lots of bright, indirect light, and watering it according to its requirements.
Another reason your hoya’s leaves are turning yellow could be a pest infestation.
The most common pests observed on hoya plants are scale insects, mites, mealybugs, aphids, moths, gnat, and thrips. The first three on the list are more common in indoor plants, while the last four are more often seen on outdoor plants.
These insects cause yellowing leaves when they bite into and suck the sap from the plant’s foliage. They also secrete honeydew on the leaves which encourages the growth of mold.
This mold can be thick and obstructive enough to inhibit photosynthesis, hence the further yellowing and wilting of the leaves.
The longer the infestation is left unchecked, the more stunted the plant will become, and it may eventually die.
If you see any pests on your hoya, you need to remove them as soon as possible.
You can wipe the leaves down with a cotton ball dipped in rubbing alcohol. Make sure you wipe both sides of the leaf.
You can also place the plant in the shower and let the stream of water knock the pests off the leaves and stems.
If the infestation is large and the above methods do not work, you might have to remove the affected leaves and stems using a sterile pair of scissors. Dispose of the debris properly.
You can also spray an insecticide on the plant. Do this in the late afternoon so the wet leaves do not burn under the sun.
Alternatively, you can make a neem oil spray by mixing two tablespoons of neem oil into a spray bottle full of water and spraying the solution onto the affected areas.
Repeat your chosen treatment once a week for as long as necessary, until all of the pests are gone.
If there are too many pests and the damage is too severe, you might have to discard the plant and start anew. In this case, bury the plant in the ground. Never throw it in the compost because you might end up infecting your other plants.
Hoyas are popular, low-maintenance houseplants that have beautiful foliage and flowers that add color to any indoor space. They are great starter plants because they are relatively easy to care for.
One of the most common problems experienced by hoya owners is the yellowing of their plants’ leaves.
The most common causes of yellowing hoya leaves are incorrect watering, improper lighting, poor water quality, temperature changes, fertilizer problems, lack of nutrients, and pests.
Image: istockphoto.com / Giovani Dressler