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With such beautiful foliage and blooms, it's not hard to see why Hoyas are such popular houseplants. Whilst generally easy to care for, they are prone to a number of common houseplant problems. This article is going to help you identify why your Hoya leaves are turning yellow and show you how to restore your plant to perfect health.
Hoya plants commonly get yellow leaves due to overwatering or poorly draining soil. Other causes include temperature stress, fertilizer problems, incorrect lighting, old age, acclimation, pests, or disease. The pattern of yellowing and growing conditions will help you identify and fix the problem.
Why Are My Hoya Leaves Turning Yellow?
Hoya leaves turn yellow when they are grown in conditions that cause your plant stress. Hoya plants originate from tropical and subtropical regions of southeast Asia and northern Australia, where they typically enjoy warm, wet, humid conditions. Preventing Hoya leaves turning yellow is largely about providing them with similar conditions to their native environment.
Overwatering
The most common cause of yellow leaves on Hoya houseplants is overwatering. Excessive water or poorly draining soil prevents the roots from functioning normally, which leads to negative impacts on the rest of the plant.
Rather than excess water being a problem, it is the fact that waterlogged soil prevents aeration, and roots need a steady supply of oxygen to remain healthy.
This results in chlorosis of the leaves, where chlorophyll begins to breakdown in the leaves, causing generalized yellowing in many leaves at once.
The yellowing often affects the lower leaves first. Of note, the leaves may be slightly swollen, limp, and soft, and you may also see brown leaf tips.
This is quite a critical problem and needs to be addressed urgently. Firstly, check the plant is not standing in a saucer of water and that there are drainage holes in the base of the pot. You will be surprised how common it is to find pots with no drainage holes and it invariably leads to the death of the plant if not addressed.
The next thing is to think about how often you have been watering your Hoya. You should only water most Hoya plants once at least the top few inches of soil feels dry to touch, and it is often better to err on the side of underwatering, rather than risk overwatering your plant.
If the soil feels soggy and there is any evidence of root rot, the best approach is to repot as soon as possible. Tip the plant from its pot and inspect the roots. If some of the roots look black/brown and are mushy and have an offensive smell, these are rotten and should be pruned off. Leave only the healthy roots and repot your Hoya into fresh soil.
Once repotted, only water very lightly and then avoid watering again until the soil feels dry.
How To Prevent Hoya Leaves Turning Yellow From Overwatering
There is often a tendency to overwater houseplants, especially on the part of newer gardeners. It is important to understand that many of the Hoya family are epiphytic. That means that they grow by attaching themselves to other plants and don’t actually grow in soil in their native habitat.
This allows them to take advantage of taller plants and to grow nearer the forest canopy. It also means that they need relatively little water.
Hoyas are more prone to overwatering than underwatering, so the soil can be allowed to nearly dry out between waterings. If they become too wet, they soon start to show signs of becoming unhappy.
Other factors that can make overwatering more likely include;
- Using a pot that is too large for the plant.
- Forgetting to empty the drip tray or cachepot.
- Potting in poorly draining soil.
- Growing in low light – This will cause the soil to stay wet for longer after watering.
- Watering on a schedule, or forgetting to check if your plant needs watered before watering.
The Wrong Potting Mix Can Cause Hoya Leaves To Turn Yellow
Choosing an appropriate potting mix is essential if you want to prevent yellow leaves on your Hoya. It will make it much more difficult to overwater your plant, and will help your plant to thrive and grow strongly.
The most important feature of a good potting mix is excellent drainage. You can make a great mix from the separate ingredients, or you can modify a commercially available option.
An ideal potting mix consists of one third cactus mix, one third house plant compost, and one-third perlite. This will provide a free-draining soil that is ideal for Hoyas.
If you are repotting, choose a pot that is only slightly larger than the original and keep those roots snug rather than giving them too much room.
Lighting Problems Causing Yellow Leaves On Hoyas
After watering and soil problems, lighting is the next most likely issue to cause yellow leaves on your Hoya houseplant. Hoyas are known as gap plants. They take advantage of gaps in the forest where light manages to reach the forest floor but still remains dappled.
The best way to reproduce this environment is to provide bright, indirect lighting in your home. An east or west-facing windowsill, or well back from a south-facing one, out of most direct sunlight will provide ideal lighting. Read my article about lighting for houseplants to learn more.
Excess Lighting
If your Hoya gets too much direct sunlight, the leaves will typically fade and can become brown or yellow, and there will often be brown scorch marks on the leaves, or brown tips or edges.
Yellowing is caused by a reduction and reconfiguration of the chloroplasts within the leaves, as the abundance of light means fewer are required to absorb light to meet the energy needs of the plant.
Don't forget that lighting levels in your home will change from season to season, so a Hoya that can tolerate a south-facing windowsill in winter, will soon develop yellow leaves in spring and summer as light levels increase.
Low lighting
Low light won't usually directly cause yellow leaves, and in fact, the first sign of low lighting can be the leaves becoming darker green, as the plant tries to absorb as much of the limited light as possible.
However, the plant will be unable to support all of its foliage for long in very low lighting, so you will see lower, older leaves start to turn completely yellow, and drop from the plant.
You will see a similar seasonal change in autumn, as light levels decline, and your Hoya houseplant adapts to lower light levels.
The other problem that can arise is that the plant will grow very slowly in low light levels, and it will take it a long time to use the water in the soil after watering.
This can make it extremely easy to overwater your plant, causing it to develop generalized yellowing in a similar pattern to overwatering. Your Hoya should always be placed in a bright location, and you may need to adjust its position through the year.
Temperature Stress And Drafts
Most Hoyas are unable to tolerate constant temperatures below 50°F (10°C), although some can cope with short exposure to cooler temperatures. If your Hoya is placed next to a drafty window or if left outside as the cool autumn nights approach, it can cause considerable stress to the plant.
The first response will be for it to develop multiple yellow leaves, affecting older and very young foliage first.
Hoyas are more capable of tolerating high temperatures, as long as their soil is kept moist and humidity remains high. Most Hoyas can tolerate temperatures of up to 95°F (35°C) without too much trouble.
The main issue with high temperatures is when they are exposed to warm drafts, which cause both temperature stress but also typically reduce local humidity. This can result in dry, yellow leaves, as well as brown leaf tips and edges.
I like to use a digital thermometer in the same room as my houseplants to keep an eye on temperatures. I use this one that records the current, maximum and minimum temperatures, to give me a really good idea of whether the plant has been exposed to temperatures outside of its comfort zone.
Pests
While Hoyas are fairly resistant to pests, a plant that has been weakened due to poor growing conditions will be susceptible to a pest infestation. Spider mites, thrips, mealybugs, aphids and scale can all be found on Hoyas.
These sap-sucking houseplant pests typically cause an irregular pattern of leaf yellowing due to direct leaf damage where the pests have fed. Entire leaves can turn yellow in a bad infestation, but otherwise, you may see irregular yellow leaf spots, as well as other evidence of the pests.
It's generally a good idea to check your Hoyas for pests every time you water them. Check both sides of the leaves and along the stems. Treating an infestation early can save a plant without significant damage, whereas a bad infestation may result in the plant dying.
Isolate any affected plant to prevent spread and treat repeatedly to eliminate the pests. You can read my guide to identifying, treating, and preventing houseplant pests to learn everything you need to know.
Disease
Hoya plants tend to be more resistant to disease problems than many houseplants. This is in part due to the waxy cuticle on their leaves, which provides a degree of protection.
However, an overwatered Hoya, or one subjected to significant stress due to poor growing conditions can be weakened and become susceptible to disease.
Look out for signs of root rot, or black/brown/yellow spots on the leaves or stem, that spread over time, which are the common signs of disease.
If you think your plant has a disease, isolate it immediately from your other houseplants to prevent the disease spreading. Prune off all affected foliage using sterile pruning shears and dispose of the cuttings.
Underwatering
Though Hoyas can tolerate dry conditions compared to many house plants, leaves will turn yellow and crispy if they do not receive enough water.
Underwatering should not be your first thought when you see yellow leaves on your Hoya. Make sure to rule out the more common issues first.
The entire plant will look dehydrated, and the soil will be completely dry if underwatering is the cause of the problem. Older leaves and younger, more delicate foliage are most at risk of damage from underwatering, so are likely to be impacted more than the foliage on the rest of the plant.
Check the soil with your fingers and if it feels very dry give the plant a good watering. It should show signs of recovery over the following days but leaves that have become too dry are unlikely to recover.
Nutrient Deficiency
Hoya leaves can turn yellow if they suffer from a nutrient deficiency, the most common of these being nitrogen deficiency. The good news is that this can be corrected.
How Does Nitrogen Deficiency Manifest Itself?
It's true that old leaves on many houseplants will go yellow and fall as they reach the end of their life cycle. When they do this, they have a dry, almost leathery texture to them.
With nitrogen deficiency, the yellowing will be more pronounced and the texture will become flaccid and weak. It will spread from the older section of the plant to the newer tips which will start to curl and look anemic. In combination, this is a sure sign that nitrogen deficiency is the cause of yellow leaves on your Hoya.
It is important to note that most houseplant potting mixes will contain sufficient nutrients to prevent nitrogen deficiency for up to several years. If you have recently repotted your plant, or if you regularly fertilize your Hoya, then nitrogen deficiency will not be the issue.
How To Fix Yellow Hoya Leaves Caused By Nutrient Deficiency
You should simply start fertilizing your Hoya houseplant every 4-6 weeks with a dilute fertilizer solution. You could use a specialist houseplant fertilizer, but a standard, balanced plant fertilizer, applied at half strength is perfectly suitable.
It is unlikely that those leaves that turned yellow will recover but don’t be too alarmed by this. The plant will manage fine even when they drop off and you will soon have plenty of new growth.
Hoya Leaves Turning Yellow Due To Acclimation
There are a number of causes of Hoya leaves turning yellow that are natural and to be expected. The first is acclimation. This occurs when a plant adapts to a change in conditions.
It is normally most noticeable when you first buy a plant and bring it home. The plant is likely to have been growing in perfect conditions in the plant nursery, and when it comes into your home, there will often be a change to less optimal growing conditions.
The plant may respond by shedding some older foliage, which will usually turn yellow first, before dropping from the plant.
If you notice yellowing of a small number of lower leaves within the first 6 weeks of bringing your plant home, double check to ensure you are providing good care, and then just wait. the plant will stabilize and the yelowing will stop.
A similar situation can arise in autumn when light levels are dropping and the plant cannot support as much foliage as it could during brighter spring and summer days.
Ensure there is not another problem causing the yellowing, and try to optimize the limited available light by moving your plant closer to a window. After this, just sit back and wait, as the yellowing will soon stop.
Old Foliage
Similar to the scenario above, your Hoya will sometimes shed a few lower, older leaves. This happens when your plant prioritizes new growth. As long as this is only happening to a few leaves at a time, then this is nothing to worry about.
Conclusion
In this article, I've tried to cover all of the potential causes of Hoya leaves turning yellow. This is so you can go through each one and compare the symptoms I describe to those that your plant is experiencing.
I find that taking a systematic approach to many houseplant problems is the best way of identifying the correct issue and being able to fix it properly.
Focus on good plant care and most of the issues we have looked at will take care of themselves. Above all avoid overwatering and ensure your Hoya is planted in well-draining soil, as these are the most common causes of problems.
