Houseplants are beautiful additions to any residence; they provide needed oxygen in addition to being aesthetically pleasing. However, houseplants sometimes develop nasty-looking, troubling yellow spots on their leaves. This is a sure indication that your houseplant is having a rough time, so you never want to ignore this issue. You'll need to figure out which of a few common problems is causing the yellow spots and then treat your plant right away.
Water and Nutrients
The Garden Helper explains that underwatering, overwatering, and nutrient imbalances (specifically nitrogen, magnesium and iron) cause plants to develop yellow spots. Water and nutrient imbalances sometimes go hand in hand for houseplants because the amount of water present in the soil impacts how the plant is able to absorb nutrients. This is especially true because the soil for houseplants doesn't get as naturally rejuvenated with more nutrients the way soil outdoors does; this is why experts recommend using mild fertilizers on houseplants from time to time.
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Repotting your plant will get it into soil that is of the proper moisture content and will ensure that the soil around your plant still has enough nutrients. It also gives you a chance to make sure the roots of the plant aren't pot-bound. This problem also can cause yellow spots because it impacts how the roots can take up water and nutrients.
All green plants have cells called chloroplasts that produce chlorophyll, the chemical that makes plants appear green. According to Argonne National Laboratory, when a plant doesn't get enough light, it doesn't produce as much chlorophyll and therefore may turn yellowish or white. Additionally, too much sunlight concentrated on one area may kill plant cells and therefore result in the same problem. According to The Garden Helper and Purdue University, water spots can act like little magnifying glasses on plants, increasing light intensity, and thus pepper the plant with yellow spots after a watering.
Disease and Infestation
The Garden Helper, Purdue University and Planet Natural all assert that certain pests, bacterias and fungi cause yellow spots on plants. All of these issues basically mean that some organism is munching away at a spot on your plant and using it as a food source.
When you purchase a houseplant, it usually will come with basic care instructions. These will tell you the susceptibilities of the plant, how to water it, the proper nutrient and soil pH levels and how much sun it needs. Paying attention to these care instructions should eliminate most of the problems that cause yellow spots.
If you have a pest, bacteria or fungi problem in your plants, it's very important to handle the plants properly to avoid the issue from spreading. This means wearing gloves and reading the instructions on any treatment product. If products don't seem to be working, cut your losses and remove the infected/infested plant(s). It's better to lose one or a few than to lose all of the plants in your home.