Soluble Salt Damage: The Secret Killer of House Plants

In the hands of some people, house plants race down the road to death as soon as they're brought home. Then there are other caretakers who can keep them alive for a few months only to watch a slow but steady decline. I suspect many of their house plants die of soluble salt damage. Brown leaf tips, not much new growth, new leaves that don't attain normal size, and loss of lower leaves all indicate salt damage, a problem few house plant owners ever hear about.

In the eight years I worked as a grower running a production greenhouse at a prominent public conservatory, I didn't worry much about soluble salt build up. We watered the plants with hoses and excess water ran freely through the drainage holes onto a gravel floor.

Dealing with my own house plants is a different story. Like most people, I keep saucers under my house plants and cover the plain growing containers with baskets or ornamental cachepots. When I water and fertilize, I know I'm also adding soluble salts, and I have to pay attention to keeping the build up under control.

Where do these salts come from? Soluble salts are dissolved minerals that occur naturally in tap water and the amount and identity of them varies from one geographic location to another. Fertilizer, while necessary to healthy house plants, also consists of soluble salts. If you have ever put water on the stove to boil and forgotten it to the point where it just boiled dry but didn't burn the pot, you may have seen a chalky residue in the pot. As the water evaporated, the natural salts were left behind. The same thing happens in your house plants.

Month after month, watering after watering, we add to the salt build up in our house plants until the small, sensitive feeder roots burn away from high salt concentration. These damaged roots can start to rot, or the house plant simply suffers from lack of an adequate root system.

In addition to the symptoms shown by the house plant itself, the pot will show evidence of what's going wrong. If the house plant is in a clay pot, you'll see a dry white or yellow residue on the outside of the pot, around the rim and drainage holes. Because clay is so porous the salt will seep into any part of the pot. In a plastic or ceramic pot, the build up will be a crust around the rim or on the surface of the soil.

Regular leaching will prevent the build up and should be done about every four months. If the plant is small enough to move easily, take it to the sink, shower or laundry tub. Remove the saucer or ornamental basket or container, and pour lots and lots of water through the growing pot. Some folks are afraid to do this, because they've heard warnings about over watering, but this will not cause over watering if it can all run out. You are essentially rinsing the soil and diluting the salts. Let it drain completely and don't forget to clean the saucer before putting the house plant back. If the house plant is too big to put in a sink, try taking it to a garage or patio and using the hose.

If the crusty white or yellow build up is already present, scrape it off with a knife or a dish scrubber. Avoid letting the particles fall back into the soil. If there is a crust on the soil itself, scrape off the top ½ inch of soil and add the same amount of fresh potting soil. Sometimes it's best to simply repot the house plant into a clean pot.

To keep house plants from accumulating salt build up, don't use water processed by a water softening system unless it has a deionizer. Always put house plants into containers with drainage holes. Water thoroughly so that some water runs out into the saucer, then promptly empty the saucer, before the water can be reabsorbed.

Just about every house plant article you'll read will warn against over watering or letting the plant sit in saucer full of water, but for some reason, few mention soluble salt build up. Unfortunately, I would say this is the second most common cause of house plant death, behind the over or under watering mistake.