Hoya Is Dying
Hoya is a genus of easy-to-grow tropicals that make excellent houseplants for beginners and experienced gardeners. These ornamental, epiphytic vines only require bright indirect light and good drainage to thrive. The thick fleshy leaves of Hoya store water for use by the plant much like succulents, so you only need to water them once the potting material has dried. Hoyas prefer high humidity levels of 50-60%, which will help the potting medium to retain moisture longer.
Most problems result from overwatering Hoya plants. Fungal diseases and pests can be attracted to plants that have been stressed by either overwatering or underwatering. The plant will display signs of damage such as yellowing older leaves, brown leaf margins, black or brown-colored spots on the stems and leaf axils, a wilted overall appearance, or the drying up of flower buds before they open.
Pest infestations may result in very different problems. Sooty black mold growing on leaves and stems could result from various sap-sucking insects, as can a sticky, clear liquid found on the leaves. Mites are indicated by the presence of wooly or webby material in the leaves and the joints of the plant as well as a stippling of the leaf color where the mites feed.
Hoya Leaves Turning Yellow
Yellowing leaves on hoya can be due to a few factors. Sun exposure that is too strong will bleach and even burn the leaves. Although Hoya likes bright light, it needs to be filtered indoors, ideally coming from a west or east-facing window. Hoya growing outside should be placed in a spot that receives protection from the sun at the hottest part of the day or that provides continuously dappled sun from a pergola or deck cover.
Overwatering can stress plants and rot parts of the stems and leaves, preventing photosynthesis and yellowing older leaves. Underwatering can also result in the yellowing of older leaves. Affected leaves may also have crispy, brown leaf margins.
When the plant seems to be yellowing all over evenly and from the center of the leaf outward, the cause may be a lack of nutrients in the potting mix. Fertilize Hoyas once a month with a liquid fertilizer formulated for succulents during the active growing period of spring and summer.
Sap-sucking pests such as aphids, mealybugs, and scale insects are the most common pests to appear on Hoya plants. These pests attack fleshy leaves and stems, and if left untreated, will eventually cause secondary problems, such as an infestation of other insects due to the sticky honeydew that is produced. Manual controls are very effective when the infestation is caught early. Spraying the plants with a strong jet of water, concentrating on the undersides of the leaves can help to kill off aphids and mealybugs. Wiping Scale insects off the plant with a damp towel or cotton pad will control a minor outbreak. Insecticidal soaps may be needed if the outbreak does not stop. Follow the manufacturer's recommendation as to how often and how much to apply. Reapplication may be needed for total control.
Fungus gnats can become a problem when drainage of the potting mix or container is poor. Fungus gnats thrive in the soil of overwatered plants and feed on any algae present in the soil, roots, and root hairs of the plant itself. The small black gnats can spread to other plants, readily becoming a large nuisance to get rid of. Prevention is key to avoiding fungus gnat outbreaks. Allowing pots to dry out between waterings, emptying saucers and cache pots of standing water, and using new, clean potting soil when replanting any houseplant are necessary for good houseplant gardening hygiene. Using yellow sticky traps placed near or in the pot of infected plants will help to control the amount of adult fungus gnats and provide a gauge of the extent of the outbreak.
The most common diseases of Hoya plants are the fungal diseases of Botrytis (gray mold) and root rots such as Pythium, Phytophthora, and Rhizoctonia subspecies. All of these diseases strike when plants are weakened by overwatering. Botrytis affects the stems and leaves of the plant and is easy to spot by the white, gray, or even dark brown mold that develops. All affected parts of the plant need to be removed as soon as possible to reduce the chance of Botrytis spreading. Cool temperatures, low light, and overwatering invite Botrytis to attack vulnerable plants.
Root rots are a group of fungal diseases that can cause the root system to fail and eventually die, killing off the whole plant. Hoyas are susceptible when overwatered for a long period. The damage may take a while to show, due to the thick waxy leaves. Brown and black spots on the stems and leaves are one sign that damage has been done. The roots will also turn gray, brown, or black and become mushy. The only treatment for a houseplant at this stage is to remove it from the pot, cut off any damaged roots, and repot in a container with excellent drainage and a potting medium that is loose and free draining. Watering only when the potting material has dried out is also recommended to allow the plant to recover.
Hoya Is Not Blooming
Hoyas flower only after the plant has reached a mature age, around 5-7 years old. Once flowering starts, there are a couple of things to keep in mind to encourage more blooms. Hoyas need the right level of light to produce flowers. Bright indirect sunlight is perfect for these tropical plants. An east or west-facing window will give them strong enough light to thrive while protecting them from sunburn and scorching of their fleshy leaves. Once your Hoya begins to bloom, do not deadhead it when the flower dies back. Let the flower fall off naturally. The remaining stem will produce another flower the following season. Fertilize your Hoya only during the active growing season of spring to late summer. Over-fertilization will not encourage more flowers, only dense foliage that may be weak and more susceptible to pests or disease.
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Author Robbin Small - Published 04-05-2023