Syngoniums getting brown spots
Hello! I am currently keeping maybe 10 or so different varieties of syngonium indoors as houseplants, all grouped together on the same shelf. Most are still quite small. I'm not sure when it started but lately I've noticed that every single plant is having an issue where a leaf gets a small or large dry, brown spot outlined with a pale yellow. Or some of the back edges get brown, especially on newly growing leaves. I've checked the roots on a few of them and as far as I know they look fine. And I can't seem to see any visible pests. They're in low light conditions. What might the issue be and what could I do? Nervous about treating with an oil or soap as a precaution because Bayer Advanced neem oil just entirely wilted my ajuga.
Certified GKH Gardening Expert
The neem oil should be sprayed in low light conditions. This will burn most crops if they are in direct light. What you describe sounds like an iron deficiency. This is common in plants that prefer acidic soil. It is a sign that your pH may be starting to drift too high. I recommend adding iron sulfate to the top of the soil. This will break down with normal watering, and kill off anything in the soil as well as bring down your pH enough to put it back at the correct level.