Soluble salts may accumulate on the top of the soil, forming a yellow or white crust (pdf). A ring of salt deposits (pdf) may form around the pot at the soil line or around the drainage hole. Signs of excess soluble salts, in indoor plants, include reduced growth, brown leaf tips, dropping of lower leaves, small new growth, dead root tips, and wilting. Soluble salts are minerals dissolved in water. Fertilizer dissolved in water becomes a soluble salt. When water evaporates from the soil, the minerals or salts stay behind. As the salts in the soil become more and more concentrated, it becomes more difficult for plants to take up water. High levels of soluble salts damage the roots directly, weakening the plant and making it more susceptible to attack from insects and diseases. One of the most common problems associated with high salt levels is root rot.
The best way to prevent soluble salt injury is to stop the salts from building up. When watering, allow some water to drain through the container and then empty the saucer.
Indoor plants should be leached at least every 4 to 6 months. To leach plants, pour excess water on the soil and let it drain completely. The amount of water used for leaching should equal twice the volume of the pot.