Keeping houseplants is a source of satisfaction for many. But when plants are not thriving it can be concerning and confusing.
As soon as a leaf yellows or develops a brown spot, many reach for fertilizer or household pesticides, neither of which is an appropriate first response.
Yellowing, brown edges, leaf spots or drops are all symptoms something is ailing a plant and cultural or environmental conditions are often the culprit. Knowing what to look for can alleviate houseplant woes.
Many plants go through an adjustment period whenever they are moved. This can happen whether it’s from the nursery to a home, the living room to a porch, or one window to another.
This may cause yellowing or leaf drop but the plant will eventually acclimate if in favorable conditions. If the yellowing continues longer than a few weeks, place the plant in another spot and change its watering schedule slightly.
Yellow leaves can also mean the plant is overwatered. A great way to decipher watering issues is to carefully remove the plant from its container and look at the roots.
With some exceptions, healthy plants generally have white roots. If the roots are rusty orange to light brown it is underwatered, and if the roots are dark brown to black it is overwatered.
Gently place the plant back in the container and adjust the watering schedule accordingly. If overwatering is the issue, withhold water until the soil is quite dry and gradually begin a new watering schedule. After two weeks, apply a water-soluble, houseplant-specific fertilizer. If no improvement is seen in the next two weeks, repot in fresh soil.
Yellowing may also occur if a plant needs to be fertilized. Depending on what nutrient is needed, yellowing may begin on the outer edges of leaves, or from the vein outward, or the leaf may even curl. Become familiar with the fertilization needs of each species. Occasionally a plant needs fertilization when it becomes root-bound and may simply need to be repotted into a larger container.
Brown edged leaves may indicate an erratic watering schedule or exposure to cold drafts. Another cause of brown leaf edges is an accumulation of fertilizer salts on containers. If other issues have been eliminated and the brown edges continue, scrub the edges of the pot and flush the soil with clear water.
Most common insect pests on houseplants include scale, fungus gnats, aphids, spider mites and mealybugs. If the plant is heavily infested with scale, it is best to discard it. Fungus gnats can be greatly reduced by letting the plant dry completely between waterings. Aphids can be controlled by washing away with water or using insecticidal soap. Spider mites often affect already stressed plants so keeping plants healthy is the most effective control measure. Horticultural oil or insecticidal soap may be used for spider mite infestations. Mealybugs can be wiped away with a cotton swab soaked in rubbing alcohol.
When using pesticides, make sure they are labeled for indoor use, and read and follow all label directions.
If the problems persist, Master Gardener volunteers and Horticulture Educators are available to provide assistance at the Illinois Extension office. Also, a houseplant guide is available at go.illinois.edu/CaringForHouseplants.
Sarah Vogel is a Horticulture and Natural Resources Educator serving DeWitt, Macon and Piatt Counties. The Green Thumb page is coordinated by DeKalb County Master Gardener Janice Weber.