Gardening experts say the best way to avoid killing your houseplants is by touching the soil before watering your plants. Plant roots need air to breathe, so over-watering soil can cause them to suffocate. If infestation is your issue, a misting spray bottle with a small concentration of peppermint soap can keep mealy bugs and fungi away. Putting in a little effort to care for indoor plants is worth the return since plants can naturally purify the air and have been proven to reduce stress.