Hoya leaves turn yellow when there is an environmental factor causing the plant stress. You can narrow down the exact cause of the discoloration by closely examining the plant’s growing conditions and the pattern of the yellowing.
The most common causes of yellowing hoya leaves are overwatering, underwatering, incorrect soil type, temperature changes, pests, too much or not enough light, and transplant stress.
In this article, we discuss the different causes of yellowing hoya plant leaves and how to remedy each one.
Why are my hoya plant leaves turning yellow?
Overwatering
Overwatering is the most common cause of yellowing hoya leaves. Both excessive water and poorly draining potting medium can contribute to the problem.
It is not the water that harms the plant, but the fact that the plant’s roots are unable to receive oxygen because they are waterlogged. Plant roots need access to oxygen to remain healthy and survive.
When the roots are compromised, they also lose their ability to absorb nutrients from the soil. The result is chlorosis, whereby the plant’s ability to make food for itself is hindered. With the loss of its chlorophyll, the plant’s leaves will turn yellow. The leaves nearest the base of the plant are the first to change color. They will also become swollen and limp, and will be soft and mushy to the touch.
When a hoya plant’s leaves have turned yellow from overwatering, it is usually a sign that the problem is serious and you will need to act fast to salvage the plant.
You can check the hoya’s roots to gauge how serious the situation is. Uproot the plant and wash off any soil. If there are parts of the roots that are brown or black, that means the plant has root rot. Cut off the rotten roots, air-dry the plant, and repot it using new, well-draining soil, in a pot that has drainage holes at the bottom.
The frequency with which you water your hoya is also something to consider. You only really need to water the plant if the top two inches of the soil are dry to the touch. If the top two inches are still moist, wait a day or two before checking the soil again.
Hoya plants are epiphytic by nature, meaning they attach themselves to trees or other plants and do not actually live in soil in their natural environment. They use the trees to reach the forest canopy and do not really need much water to survive. This makes it easier to overwater the plant than to underwater it. It also means the plant will be okay if left to dry for a while between watering.
Make sure you use a pot that is not too big for the plant so that the soil does not retain more water than necessary. If the pot has a drip tray, make sure to empty it once the pot has been given ample time to drain. Use well-draining soil rather than compacted soil such as clay.
Underwatering
Hoya plants are more prone to overwatering than to underwatering, but that does not mean underwatering does not happen. If you neglect your hoya plant to the point where the soil has dried up, the leaves will turn yellow and become crisp.
When you see a hoya plant with yellow leaves, underwatering is not at the top of the list of causes, so make sure you rule out the more common causes before considering this.
If the plant is underwatered, the entire plant will look dehydrated and the soil should be bone dry. The youngest and oldest foliage are the most susceptible to damage.
It is very easy to remedy an underwatered hoya plant. Simply flush the soil in the pot until you can see the excess water flowing out of the drainage holes.
Soil type
Using the wrong kind of soil can also cause the hoya’s leaves to turn yellow. As mentioned above, a dense, compacted soil retains too much water, resulting in the same conditions as overwatering.
If you use a well-draining soil mix that allows excess water to flow through it easily, the chances of overwatering the plant decrease dramatically.
You can buy succulent or cactus soil mix from a store or make it yourself. Just mix one part of normal potting soil to one part compost to one part perlite.
Make sure you choose a pot that is only a little bigger than the plant’s last pot so that the roots are snug enough, without giving them too much space.
Too much light
Hoya plants take advantage of the gaps in the rainforest canopy to get their required daily light. Since this is what the plant has adapted to in its natural habitat, it makes sense to try and replicate this in your home by bringing in bright, indirect light. A west or east and south-facing window will work just fine for the hoya.
When your hoya gets too much light, the leaves’ color will fade and become yellow and even brown. There might even be scorch marks on the leaves, leaving brown tips and edges.
This happens because the chloroplasts in the leaf tissue will reconfigure and reduce due to too much light. When the plant detects too much light, it thinks it needs fewer chloroplasts because of the concentration of light it is getting.
You may need to relocate your plant if the spot it is in suddenly has more light than normal, such as during the spring and summer.
Not enough light
When the hoya plant does not get enough light, the leaves do not immediately turn yellow. In fact, the leaves of the hoya plant become even more green as the plant compensates and tries to absorb as much light as it can.
The leaves will start to turn yellow when the plant decides to prioritize its top, younger leaves with its limited resources. The older leaves at the bottom are let go in order to prolong the life of the plant.
Hoya plants grow much slower in poor light, and the water in the soil will also evaporate at a slower pace.
It is very easy to correct a light deficiency for your hoya plant: simply transfer it to a location where it can get the light it needs.
Temperature changes
Hoya plants cannot survive in temperatures below 50 degrees Fahrenheit. Even if you bring your plant indoors for the winter, placing it near a door or window where cold drafts can reach it could still affect the plant negatively. This can cause the leaves to turn yellow, affecting the youngest and oldest leaves first.
Hoya plants are much more tolerant of high temperatures and can survive temperatures up to 95 degrees Fahrenheit, but they do not do well in the presence of warm drafts. The warm air reduces the humidity around the plant and dries it out, hence the yellowing of the leaves.
You can keep your plant safe from temperature extremes by using a thermometer to monitor the temperature in and around your home. Make sure you also check that there are no cold or warm drafts passing through the plant’s location.
Pests
The pests commonly found on hoya plants are those that feed on the plant’s sap. This plant is fairly resistant to these insects, but if the plant is weakened and compromised, the pests take advantage of the situation.
The most common pests for hoya plants are scale insects, aphids, mealybugs, thrips and spider mites.
When they feed on the hoya’s leaves, they leave spots that coalesce to form yellow splotches. In a large infestation, entire leaves can turn yellow.
The best way to prevent a pest infestation is to regularly check the plant for pests. Catching an infestation early is key to preventing further damage to the plant.
Make sure you separate the infested plant from your other plants so that the pests cannot spread.
You can remove the insects by blasting them with the spray nozzle of your garden hose, or you can use neem oil. Wipe the leaves with neem oil on a cotton ball once a week for a month to make sure all the insects are dead.
Transplant stress
When you take the hoya home from the nursery, it is normal for some of its leaves to turn yellow. This is because the plant is still trying to adjust to its new surroundings.
When a plant is grown in a nursery, it has the best living conditions. When you take the plant out of its comfort zone and into a place where almost every aspect of its life is different, it will become stressed.
The only thing you can do in this situation is simulate the plant’s natural habitat as best you can so that its transition to its new home is as smooth as possible. Eventually, the plant will adapt to its new surroundings and make a complete recovery.
Conclusion
When a hoya plant’s leaves turn yellow, it is an indication of stress: an environmental factor is causing the plant’s leaves to discolor. Inspecting the plant’s leaves, soil and living conditions will help you determine what exactly is the cause of the problem.
The most common causes of hoya plant leaves yellowing are overwatering, underwatering, incorrect soil type, temperature changes, pests, too much or not enough light, and transplant stress.
Image: istockphoto.com / MilenaKatzer