Prevent salt build up on the soil of houseplants

Q uestion: I inherited a few houseplants from an aunt who passed away a few months ago. I’m not sure what they are, but they seem to be doing OK. I have them in our front picture window which receives a good amount of light. I’ve noticed, though, that on top of the soil in several of the pots is a white chalky substance. Is this something I should be worried about? Is some kind of insect making it?

Answer: The white, chalky substance on top of your houseplants’ soil is indicative of a build-up of fertilizer salts within the potting soil. Houseplant growers who over-fertilize their houseplants or water improperly will often see this white crust covering the soil.

Regardless of the exact species of houseplants you have, be sure not to over-fertilize them. All too often well-intentioned houseplant growers go overboard with the fertilizer, thinking more is better. For houseplants, fertilization should be minimal and should only take place from late March through August. I recommend using a liquid, organic fertilizer formulated specifically for houseplants diluted to half the recommended strength.

Too much fertilizer, or fertilizer applied during the fall or winter months when the plants are not in an active state of growth, can lead not just to a salt crust on the soil’s surface, but also browning of the leaf tips. As the fertilizer salts travel through the plant, if they aren’t needed for growth, they collect at the tips of the leaves, causing leaf tip burn.

If you haven’t fertilized, or your fertilizer regimen matches the one I describe, then improper watering could be causing a build up of salt on the soil of your houseplants. When watering houseplants, it’s important that at least 20 percent of the volume of water that goes into the top of the pot drains back out the bottom.

Irrigation water should flush through the container’s soil and exit out the drainage hole in the bottom of the pot. As the water travels through the soil, it flushes out any excess fertilizer salts, preventing them from building up and causing the salt build up you describe.

Proper houseplant watering means taking the pot to the sink or bathtub and running the water through the pot and allowing it to fully drain before putting the pot back on display.

For larger houseplants that you’re unable to lift into a sink or tub, limit the fertilizer to only once or twice a year. And don’t allow any water to sit in the saucer beneath the pot as this could either lead to root rot, or cause the fertilizer salts to be reabsorbed back up into the soil and collect on its surface.

Most potting soils used to pot up houseplants contain a slow-release form of fertilizer, so there’s no need to add supplemental fertilization for a year or two after buying a new houseplant or repotting an existing one with new soil. Doing so will only lead to salt build up and/or leaf tip burn.

Changing your watering technique and fertilizing schedule should eliminate the white crust on the soil of your houseplants within a few weeks.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.