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Have you tried your hand at growing hoya? Leaves turning yellow indicates a problem with chlorosis, which is a condition that can be caused by just a handful of factors. Common causes of hoya leaves turning yellow are:
- Using the wrong type of potting soil
- Growing hoya indoors with lower than required temperatures or room humidity
- Insufficient lighting
- A nutrient deficiency that can be fixed with an appropriate fertilizer
- Pests sucking the nutrients out of the leaves
Water, air and sunlight are what every plant needs for chlorophyll production, but like most things, too much of a good thing isn’t always good.
The 3 Things Hoya Plants Need to Restore Green Foliage
1 – Fast Draining Potting Mix
Despite having hundreds of species of hoya plants, the majority are all epiphytes, meaning the natural habitat is the bark of trees in conditions reminiscent of the rainforest. Mimicking that environment can be tricky.
Some species do fine when grown like air plants without any potting medium, perhaps used as a decorative plant affixed with a hot glue gun to a strip of bark, hung on the wall of your bathroom. That can work, but it’s not always a success.
Some species of hoya really do need a potting medium, other than sphagnum moss. Plantophiles.com recommend the potting mix for hoya be made with a mix of 1/3rd potting soil, orchid mix, (such as fir bark, and charcoal) and perlite.
The reason the mix works for hoyas is because they need to dry out between watering so as to prevent root rot, which will discolor the leaves and eventually kill the plant. With hoya, the faster the soil drains, the healthier the plant will be.
To speed up the drainage time, an unglazed clay pot helps as it increases air flow too. It will mean the plant will need to be watered more frequently, but there’s far less of a risk of it getting overwatered.
2 – Mist the Leaves More than You Water the Base
Even with a fast-draining potting mix, not all the water will be soaked up by the roots of the plant. And that is fine because hoya plants prefer to dry out. In fact, they do better with underwatering than they will with too much water so always wait until the top layer of soil is dry to the touch before adding water.
The ideal temperatures to grow hoya plants is over 50oF (10oC) with a relative humidity of 60% to 80%. In those conditions, you should find your plant only needs water added to the base every week during the summer months, and less when the temperatures drop.
Controlling the humidity may require you to get creative, such as if you’re growing these in a sitting room and prefer a lower room humidity. In those conditions, frequent misting can help increase the humidity around the plant without making the room uncomfortably humid.
A practical way to raise humidity in only spots of a room is to wet a sponge and put it inside a plastic bag with some holes pierced in it then hang that near the plant.
3 – Bright but Dappled Sunlight is the Key Requirement
The key ingredient all hoya plants need is sunlight. Keep in mind that these plants are native to rainforests and super-hot climates, but being that they are climbers found on the bark of trees, they don’t get full sunlight all day.
The natural light they get is through the canopy of overhead leaves on trees. Full sun, all day, is likely to be too much. But they also don’t grow at ground level, so shady areas of a room indoors will have inadequate sunlight.
A lack of sunlight will cause the leaves to yellow, but overdoing it with too much (something that’s just as common with hoya plants) results in the leaves turning red with sun burn. South-facing windows get the hottest sun rays at late morning to mid-afternoon.
If you need to use a south-facing window, put some space between the plant and the window to avoid it burning. The only unsuitable window for the light requirements of a hoya plant is a north-facing window which gets little to no direct sunlight.
Where you lack the sunlight, consider using grow lights to provide artificial light, which will have the same effect for photosynthesis.
The Fertilizer Fix for Hoya Leaves Turning Yellow
The above are simpler fixes to rejuvenate yellowing leaves on hoya plants that’s caused by the growing conditions. When you know you haven’t over or underwatered your plant, have sufficient light, and the right potting mix, it’s likely that a nutrient deficiency is causing hoya leaves to turn yellow.
You’ll know it if the older leaves yellow and then drop from the plant, with newer leaves growing in with a paler green and usually wrinkled, which indicates they need a little help to flourish.
The two critical macronutrients hoya plants need to rejuvenate the plant are nitrogen and potassium. A good rule of thumb for hoya plants is to feed them a nitrogen-rich fertilizer, such as 10-5-10.
The middle number is for phosphorous and it’s only recommended to switch to 5-10-5 (as an example) when your hoya plant is flowering, and that’s because phosphorous promotes blooming.
Nitrogen is what’s needed for the green foliage growth, and the potassium supports the stem growth and also helps to fend off diseases.
Problematic Pests for Hoya Plants
Hoya plants are very pest resistant. In fact, only a couple of insects can be a nuisance and those are the mealybug and aphids. Both are sap-sucking pests and since they will suck the nutrients out of the sap in the leaves, it will cause the leaves to yellow.
Aphids are more likely to invade hoya plants grown outdoors, but they can still infest indoor plants, and faster too because there’s no natural predators indoors to help keep them at bay.
If you’re growing hoya indoors and noticing the leaves yellowing, inspect the plant for signs of mealybugs, which include a cotton-like substance on the leaves, and black mold spots. While mealybugs are destructive to hoya plants, they’re also easy to get rid of.
Read More: How to Get Rid of Bugs on Indoor Plants