Clove oil, derived from the aromatic flower buds of the Syzygium aromaticum tree, is a natural product that can kill plants. When used in high concentrations, it acts as a non-selective, contact herbicide, damaging or killing any plant tissue it touches. This effect is powerful enough that clove oil has been registered and used commercially as a botanical herbicide for weed management, particularly in organic farming systems.
The Active Component and How It Harms Plants
The herbicidal action of clove oil is primarily attributed to its main active component, a phenolic compound called Eugenol. Eugenol often makes up over 80% of the oil and provides the foundation for its plant-killing properties.
Eugenol works by rapidly disrupting the structural integrity of the plant’s cellular membranes. This damage causes the cell contents to leak out, a process known as electrolyte leakage. The compromised cells quickly lose their ability to retain water, leading to rapid desiccation and visible “burn” on the foliage.
This mechanism causes the plant to dry out almost immediately upon application, distinguishing it from systemic herbicides that must be absorbed and transported throughout the plant. The effectiveness of clove oil varies depending on the plant species and the presence of leaf epicuticular wax, which affects the oil’s ability to penetrate the leaf surface.
Clove Oil as a Contact Herbicide
Clove oil functions as a fast-acting, non-selective, contact herbicide, defining both its strengths and limitations in weed control. Its non-selective nature means it will kill desirable garden plants and turfgrass just as readily as it kills weeds, requiring careful, targeted application. Only the parts of the plant directly sprayed with the solution are affected.
This characteristic makes it highly effective against young, annual weeds that lack deep root systems or thick cuticles. Broadleaf weeds like common lambsquarters and pigweed are often susceptible to control with clove oil mixtures. However, because the oil does not translocate systemically down to the roots, it is generally ineffective for permanent control of established perennial weeds.
Perennial weeds with extensive root systems, such as Canada thistle, may have their foliage burned back by the oil, but they often regrow from the undamaged root crown. Effective weed control relies heavily on achieving complete coverage of the target foliage and may require repeat applications to manage perennial regrowth. Efficacy is enhanced by adding a surfactant or emulsifier, which helps the solution spread and stick better to waxy leaf surfaces.
Safe Dilution and Application Guidelines
To use clove oil as a herbicide, it must be diluted and mixed with an emulsifier to create a stable spray solution. Recommended herbicidal concentrations are high, typically ranging from 5% to 20% clove oil by volume in the final mixture. Concentrations below 5% often result in poor control. Concentrations exceeding 20% are unnecessarily costly and do not offer significantly greater efficacy.
A common household product like liquid dish soap or a commercial horticultural surfactant can be used as the emulsifier, usually at a rate of a few teaspoons per gallon of spray solution. The mixture must be shaken vigorously before and during application to prevent the oil from separating and floating on top of the water.
Application should be targeted directly at the unwanted plants, avoiding overspray onto any desired plants, including vegetables or ornamental shrubs. Since clove oil is a strong irritant, personal protective equipment (PPE) such as chemical-resistant gloves, long sleeves, and safety goggles should be worn to prevent skin and eye exposure. Although clove oil breaks down rapidly in the environment, it is highly phytotoxic and should not be used near aquatic habitats due to potential toxicity to aquatic life.