University of Maryland Extension

Mineral and Fertilizer Salt Deposits - Houseplants

mineral orchid

  • Mineral and fertilizer salt deposits usually appear as white crystallized coatings on plant leaves or as a white crust on the surface of the growing media or pot.
  • Mineral salt deposits are caused by the use of hard water that has high concentrations of dissolved substances such as calcium carbonate, sodium, and iron.
  • Fertilizer salt deposits are the result of the various components of soluble fertilizers.
  • Both kinds of salt deposits can cause harm to plants by competing for the available moisture and causing desiccation or "burning" of tissues.
  • In addition, these deposits can affect the pH of the growing media as well as block absorption of essential plant nutrients.

Management

  • To prevent mineral salt deposits use a good water source low in dissolved minerals.
  • To prevent fertilizer salt deposits follow the manufacturer's application instructions and wash off any spills on plant surfaces.
  • In both cases, avoid bottom watering or pots without drain holes and flush the growing media from the top with several volumes of pure water. 
  • In severe cases, repot with fresh potting media.
  • To reduce mineral buildup water with clear water to leach (rinse) houseplants every 4 to 6 months. Apply at least 3 times the volume of the pot of fresh water on the potting soil and let it drain completely. 
  • If a crust forms on the outside of a pot, the pot should be replaced with a fresh one. The old pot can be soaked, scrubbed with a brush, and cleaned in fresh water before reuse.
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