Dead flowers certainly attract gnats, but the attraction is not to the flower itself. Instead, gnats are drawn to the moist, decomposing organic matter created by the dying plant material. These insects are most commonly fungus gnats (species in the family Sciaridae), which are small, dark, mosquito-like flies. They seek out this environment to complete their life cycle, especially in houseplants where dead leaves or spent flowers fall onto damp soil.
The Science of Attraction
The primary attractant for fungus gnats is not the plant tissue itself, but the microscopic organisms that flourish as it decays. The larvae feed on the fungi and algae that grow in overly wet soil or on dead plant parts. As a flower dies, its tissues break down, releasing moisture and nutrients that create an ideal environment for fungal growth—the larvae’s preferred food source. Adult female gnats specifically seek out these moist, fungus-rich locations to deposit their eggs.
Moisture is a stronger lure than the dead flower itself. Waterlogged soil or stagnant water provides the high humidity and damp conditions that fungus gnat larvae require for survival and development. This explains why an overwatered houseplant with fallen petals can become infested more quickly than a dry outdoor garden bed. The gnats are following a chemical trail to a nursery and food source for their young.
The Fungus Gnat Life Cycle
The presence of dead flowers provides an opportunity for the fungus gnat to reproduce rapidly. The adult female, which is about one-eighth of an inch long, lives for only about seven to ten days, but she can lay up to 200 eggs in the top inch or two of moist, organic-rich soil. This short life span and high reproductive rate allow populations to explode quickly under favorable conditions.
The tiny eggs hatch after approximately three to six days, and the larvae emerge to begin feeding on fungi and decaying plant material. The larval stage lasts for about ten to fourteen days. After this feeding period, they pupate in the soil before emerging as new adults, ready to mate and continue the cycle. The entire life cycle can be completed in as little as three to four weeks.
Dead Organic Matter in Different Settings
The way dead flowers attract gnats differs slightly depending on whether they are in a pot or a vase. In potted plants, dead flowers or leaves that fall onto the soil surface become part of the organic debris. This debris contributes to the moist conditions that foster fungal growth. This decaying layer of material is exactly where the female gnat chooses to lay her eggs, ensuring the emerging larvae have immediate access to food.
Cut flowers in a vase, while lacking soil, can still become a breeding ground if the water is allowed to stagnate and the stems begin to rot. The decaying stems and leaves submerged in the water provide the necessary organic decomposition, often accompanied by mold or mildew, which attracts the gnats. This creates a moist, nutrient-rich sludge at the bottom of the vase, which is appealing for egg-laying. Even dried flowers, if stored in a high-humidity environment, can attract gnats if they begin to absorb moisture and develop mold.
Practical Prevention
Controlling fungus gnats is primarily a matter of managing moisture and removing the decaying material they require. The most effective cultural control method is to allow the top one to two inches of potting soil to dry out completely between waterings. This dry layer makes the environment inhospitable for eggs and larvae, and it makes the soil less attractive to egg-laying adult females.
Regularly removing any dead flowers, fallen leaves, or other organic debris from the soil surface eliminates potential food sources for the larvae. For cut flowers, changing the water frequently and trimming the stems prevents the stagnant, decomposing environment that attracts the pests. Avoiding the use of incompletely-composted organic fertilizers or soil amendments can also help, as these often harbor gnat infestations.