The Hoya plant, also called wax plant, porcelain flower and wax vine, is a member of the same plant family as milkweed. It has thick fleshy leaves, covered with a wax-like coating, which grow from a semi-woody vine. When in bloom they put on star-shaped white flowers. Though native to tropical areas of Florida, the Hoya has become a common houseplant and is traditionally grown in 3-inch pots from cuttings which have been dipped in rooting hormone and effectively established. Hoya plants can develop a number of problems, which, if effectively treated, do not necessarily have long-term effects on plant health.
A Hoya plant that does not grow, that fails to bloom, or that blooms and then deteriorates, in most cases, is not receiving enough light to support its life cycle. The Hoya plant needs 1,500 to 2,000 candles of light per day, or a minimum of 125 foot-candles of light for a minimum of 10 hours per day.
A plant that puts on blooms which fall off before opening is likely being over-watered. When you water, ensure you soak the whole root mass. Allow the upper half of the root mass and soil to dry completely before watering again. The Hoya needs to be watered more sparingly in dormant seasons, and more generously during periods of growth.
Blight presents itself as gray areas on the plant’s leaves. This leaf damage most commonly occurs at the center of the plant where moisture levels are highest, and during the winter months. If the disease is allowed to progress, leaves will become mushy as they deteriorate. Careful watering and reduction of humidity will help to reduce blight. Also, remove infected leaves from the plant and quarantine the plant from others which might be susceptible to the infection.
This condition is especially concerning for the Hoya grower because it is hard to detect. The thick and waxy growth slows disease symptoms by camouflaging the wilting pattern, so it is often too late to treat a plant when the condition is discovered. Stems will turn brown and mushy, and roots will become mushy or dry when the plant is infected. If the root rot is fungal in nature, treating the plant with a fungicide is appropriate. Reduce watering to affected plants and re-pot in all new soil.
The most obvious symptom of infestation by pests like thrips, aphids, scales, gnats and mealybugs is the presence of that insect on the plant. Use a pesticide intended for use against the specific insect that is affecting your Hoya; follow the directions for application as listed on the insecticide’s packaging.