Overwatering is the single most common mistake that kills indoor houseplants. When you give a plant too much water, the soil becomes completely saturated and displaces oxygen. Plant roots actually need air to breathe, and without it, they essentially suffocate. This waterlogged environment creates the perfect conditions for a destructive disease called root rot. Root rot decays the root system, making it impossible for the plant to absorb essential nutrients. Above the soil, you might notice leaves turning yellow, wilting, or dropping off entirely. To avoid this, always check the soil moisture with your finger before reaching for the watering can. Most houseplants prefer to dry out slightly between waterings rather than sitting in soggy soil. Ensuring your pots have functional drainage holes is another crucial step to let excess water escape.