Fluoride burn in houseplants, which manifests as brown leaf blotches or burnt leaf tips in vulnerable plants, including dracaena, spider plants, and Easter lilies, is said to be caused by perlite. However, the likelihood of that occurring is extremely remote if you use perlite-containing commercial potting soil. Fluoridated water, low soil pH, superphosphate fertilizers, and other environmental factors that have little to do with potting soil that contains perlite can all contribute to fluorine toxicity.