What causes aster leaf and flower drop

Asters are perennial flowering plants with bell-shaped, drooping flowers that trail long anthers. The flowers come in various colors, but the most common are purplish-red blooms that share the plant's near-purple namesake hue. However, for gardeners, asters are frustrating because many conditions can cause them to either lose their flowers, lose their leaves, or both.

Temperature

Asters need nighttime temperatures of at least 18.3°C or lower to produce beautiful flowers, and they stop blooming when daytime temperatures stay above 24.4°C. Rapid temperature changes, especially at warmer temperatures, can cause bud drop. Only under extreme temperatures is this bud drop accompanied by leaf drop.

Humidity

Asters prefer 55% relative humidity, and a dry indoor environment can cause bud drop. If drought is accompanied by dry soil, the leaves will drop as well. Asters prefer moderately moist soil and mulch with high organic matter, keeping the environment stable and favorable.

Disease

Purple rust (Pucciniastrum epilobii) is a fungal disease that overwinters in the form of spores and infects the undersides of aster leaves. It begins with just a few inconspicuous brown spots on the underside of the leaves, making it hard to detect. Over time, yellow-orange spores form on the undersides and tops of the leaves and gradually drop off. Water hitting these spores splashes them onto the plant. If the leaves are still on the plant, the result of leaf loss usually leads to flower drop.

Precautions

Leaves, buds and flowers are responses to stress. The aster's natural environment is protected, with abundant foliage and a humus mulch layer, deep soil, and surrounding plants that regulate the surrounding humidity, temperature and moisture and prevent fluctuations. Many leaf and flower drop problems can be solved by placing asters in an environment closely matching their own.