Your outdoor garden plants may not need a lot of attention on these cold winter days, but have you taken a close look at your indoor plants recently? A house plant with brown leaf tips, wilted leaves, lower leaves that are dropping and little or no new growth may be in trouble. All of those problems, and even plant death, can be caused by soluble salts. 

Soluble salts are naturally occurring minerals, such as sodium, chloride, boron, calcium, and magnesium, that are dissolved in water. Some of the water in Stanislaus County has relatively high levels of certain salts, but in general, all water has some salt. Fertilizer dissolved in water also turns into a soluble salt. After water evaporates from the potting soil, the salts stay behind. Eventually, an excessive amount of salt may be absorbed by the roots, move  upward in the plant, and concentrate in the leaves, causing tip burn. As salts in the soil become more concentrated, plants find it harder and harder to take up water. If enough salt accumulates in the soil, the water absorbing root tips are killed, and the plant begins to wilt and drop leaves.

To combat this problem, be sure you water correctly. Water plants enough so that some water moves through the soil and out the pot's drain hole. Then empty the drip plate. Do not allow the pot to sit in water. If drained water is reabsorbed by the soil, the salts that were washed away are taken back into the soil. The process of removing soil salts is called “leaching.”

It's a good idea to leach your house plants every two or three months. To do this, water the soil thoroughly, as you usually would. Then, after about five minutes, water again, letting excess water flow out the bottom drain holes. The first watering dissolves the salts, and the second washes the salts out of the soil.

As water evaporates from the soil surface, some of the salts may form a layer on the soil surface. If a layer of salts has formed a crust on top of the soil, be sure to remove the salt crust before you start to leach. You should only need to remove about an inch of soil to remove the salt crust. Also, clay pots can absorb salts. If the pot is coated with a white salt residue, it's best to replant in a clean container. 

For more information, consult the UC IPM Pest Notes: Houseplant Problems.

Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.