Reducing houseplant salt problems when repotting

Question:

Each spring I repot most of my houseplants. This year I have noticed quite an accumulation of salts and other deposits on the top of the soil and around the edges of the pots. I guess it has always been there, but now I see it and wonder if there is any way to reduce this when I repot.

Tommy N.
Las Cruces

Answer:

If you just repot by moving the old soil into a larger pot and adding new soil around it you do carry the accumulated mineral salts from one or more years of growth into that new potting soil. This residual salt can do damage to your houseplants, so your concern is valid.

There are a couple of ways to deal with this problem. The first is to remove all or most of the old soil when you repot. When you remove this soil, there will be some damage to the roots system. Some plants will tolerate this "root pruning", others will be injured. Minimize root damage when removing the soil by carefully teasing the soil away with chopsticks or other implements, or take the plant outside and gently wash the soil away with water from the garden hose. If you cannot get all the soil removed, you will remove much of the accumulated salt using these techniques. The washing technique also removes salts by dissolving them from any soil that remains. It also keeps the roots moist while you are removing the soil so they will not be damaged by drying. Do this is a shady place on a warm spring day so the roots will not be harmed by sunlight or by cold.

Once you have removed the soil as well as you can, you can repot into a new pot or the old pot if it has been cleaned, soaked in disinfectant (10 percent chlorine bleach), and well rinsed. By removing the soil, you may not have to move the plant to bigger and bigger containers each year. This helps keep the size and weight of your houseplants manageable. If the plants are growing rapidly, you may need to use a larger pot, but you have the option of reducing the rate at which the pots increase in size and weight.

The new soil you use should be appropriate for the plants you are growing and should be disease free. Now you are ready to return your plants indoors or to let them spend the summer vacation outside in a shady location.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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