The Spontaneous Combustion of Dead Potted Plants

Potting Soil

• Many potting soil mixes on the market today contain both organic and inorganic material. A potting soil mix may contain Styrofoam pellets, perlite or vermiculite, which are added to the mixture to promote aeration and help retain water. The potting soil may also contain shredded bark, wood or peat moss. Many mixtures may also contain different fertilizers, some of which may act as oxidizers. These will cause a fire that can spread rapidly.

Process

• Spontaneous combustion occurs via biological and chemical processes, involving bacterial decomposition that causes microbial growth and chemical changes in the material that creates heat. Organic material with moisture contents between 26 to 46 percent moisture and a temperature that exceeds 200 degrees F may ignite on its own, warms the University of Minnesota Extension. Although temperatures this high generally only occur in hay or compost piles with limited air flow that have a height of 7 feet more, cases of dead house plants in pots spontaneously combusting have been documented by fire marshals. Spontaneous combustion of organic materials is found more often in humid climates.

Other Causes

• While dead potted plants may spontaneously combust in the right conditions, a more common cause of such fires is cigarettes. When a cigarette butt is extinguished in the soil of a potted plant, it may cause the materials in the potting soil mix to ignite. According to Fire Safety Educators of Colorado, potted plant fires have been linked to almost $4 million worth of property damage and the loss of one life in Colorado. Matches and stray fireworks may also cause the potting soil mixture in a dead potted plant to ignite.

Prevention

• Keep your potted plants well watered and maintained. Discard dead potted plants promptly by throwing them into the trash or spreading the soil in your yard or garden. Do not use pots that contain dead plants and potting soil as an ashtray. Make an ashtray available in areas where someone might be smoking. Keep dead potted plants away from combustible materials such as a wood porch or deck.