Soil

• One of the greatest dangers when using a potting mix comes from contamination from untreated garden soil. The soil might carry disease causing agents that can kill your plants. Usually, this danger comes from homemade potting mixes that include garden loam in the recipe, since commercial mixes have been treated to eliminate any pathogens. However, even a commercial preparation might become contaminated after the fact. Avoid letting any soil from your yard or garden come into to contact with the container plant's potting medium. Make sure you clean all your garden tools before using them to work with your potted plants.
  
  

Debris

• Another potential problem that might result in your potting soil damaging your plants comes from organic debris and litter, such as decomposing leaves and stems. Some types of pathogens have evolved to remain dormant in these plant parts until conditions become ripe for their growth, according to Pennsylvania State University Extension. Many types of harmful bacteria and fungi can exist for several months in plant litter. Remove any plant debris or litter from your containers as soon as you discover it.
  
  

Homemade Mix

• Some authorities, such as the University of Rhode Island Extension, advise gardeners to pasteurize their homemade mixes to kill any disease causing organisms. Pasteurizing involves heating the mix to a high enough temperature to eliminate any pathogens. Heat the mix in your stove for about half an hour at a temperature between 180 and 200 degrees Fahrenheit. Also, make sure you disinfect any pots before putting the pasteurized mix into them. Wash the containers and let a solution of 1 part chlorine and 9 parts water soak in them for half an hour. Rinse the pots well using them.
  
  

Water

• A potting soil may start to grow disease causing agents, such as the fungi that cause root rot, if the container does not drain properly. A good container should have a hole at the bottom to allow water to pass through, rather than build up in the potting mix. Most containers come with drainage holes, but if your container does not have one, you can simply drill a hole on the bottom yourself.