Definition

Plants with flower buds that drop off their stems before opening are said to be suffering from bud drop.

Lack of Light

Flowering plants need ample light to thrive and some species suffer from bud drop if left in low light areas. An example is the hybrid Asiatic lily.

Hormonal Trigger

Bud drop can be caused by the plant hormone ethylene. Able to be transported in a gaseous state, ethylene also regulates the change in the color of leaves in the fall and their eventual drop off from the mother plant. The gas also causes fruit to ripen.

Ethylene Exposure

Plants, particularly those in urban areas, can also be exposed to ethylene from outside sources. Smoke, either industrial or cigarette and auto exhaust all contain ethylene.

Cut Flowers

Flowers cut from the parent plant show an immediate increase in ethylene because the gas is trying to trigger the flower to regenerate. Since the flower has been deprived of its nutrition source, it cannot respond. The ethylene gas keeps increasing until the bud wilts and drops away.

Potted Plants

Potted plants that become root bound may develop bud drop. The roots, which have outgrown their container, can no longer absorb needed nutrients, and the parent plant sheds its buds to conserve energy. This is a common problem with camellias, which are highly susceptible to many stress factors.

Source:

University of Massachusetts: Greenhouse Plants and Floriculture: Production of Hybrid Lilies as Potted Plants

Chrysal Academy: Why Do Flowers, Leaves and Buds Drop?

Aces: The Culture of Camellias, the State Flower of Alabama