Why Are My Allamanda’s Leaves Turning Yellow?

Did only the older leaves turn yellow?

Has your plant gone through a light frost lately?

Are there any tiny insect pests present on your allamanda?

Is the soil in your garden alkaline and low in nutrients?

As summer turns to fall and early winter, allamanda plants naturally drop some of their oldest leaves. This is a normal process of changing its foliage.

Temperatures below 45 degrees Fahrenheit often promote natural leaf drop, and a light frost may fully yellow a plant, followed by leaf drop a day or two later. Cool nighttime temperatures coupled with wet soil can make leaf yellowing more pronounced. During the cooler days and lower sunlight intensity of winter, keep the soil slightly dry.

Spider mites and whiteflies often plague allamanda plants. Spider mites occur in dry conditions, especially in windless, arid air. Thin webs net leaf undersides and reveal the tiny red bodies of spider mites. Wipe off the webs, increase soil watering, and spray the foliage with a water nozzle to dislodge the mites. Whiteflies can occur at any time of year. Touch an infested allamanda, and a cloud of tiny white bugs will take to the air. Use am insecticidal soap to rid an allamanda of these pests.

Infertile and alkaline soils lead to leaf yellowing and stunted growth. Allamanda responds favorably to fertilizers when they are actively growing from the spring through the fall. In conjunction with the increased watering during the warm months, apply a liquid fertilizer as part of the watering process once every two to three weeks. Use a well-balanced formulation, such as 10-10-10. Stop fertilizing in the fall when you also diminish the watering amount.

Unfulfilled watering needs often lead to yellow leaves on allamanda. Both bone-dry and waterlogged soils cause unhealthy yellowing leaves. In the winter, keep well-drained garden soil slightly moist to slightly dry. Water only when the soil becomes dry to the touch at a depth of 1 inch. Once spring warms and new leafy growth appears on the allamanda's branches, increase watering to maintain evenly moist soil. Soil moisture during the summer is important, as the intense heat and sun's rays increase the need for water.