Last month Master Gardener Debbie Nelson shared research on how houseplants can have positive impacts on our health. This month, let’s talk about keeping the plants themselves healthy.
When you purchase a new plant, reject any that have signs of damage such as spots or yellowing leaves. In cold weather, be sure to have plants wrapped before transporting them to your car. Even brief exposure to cold can cause serious damage. Place your new plant away from your other plants for 2-4 weeks so you can inspect it for insects or fungus that might develop. It is normal for plants moved to a new environment to drop a few leaves.
Light is crucial to healthy houseplants. The plant tag will often tell the light requirements. Low light plants can be placed close to a north window. Medium light plants could grow by an east window. High light plants need bright light of a south or west window. If you don’t have enough light, especially in winter, supplemental light can be provided by a fluorescent fixture placed within a few inches of the top of the plant. Symptoms of a plant not getting enough light include: spindly growth, small leaves, long spaces between the internodes of leaf clusters along the stem, and leaf loss. Too much light causes leaves to curl at the tips or develop yellow or brown blotches.
Good watering practices include using room temperature water that has not been softened. There is no simple answer on how often to water a plant. This is dependent on the plant variety, its water needs, and growing environment. One way to determine if your plant needs water is to insert your finger (to the second joint) to test for moisture. If the plant requires moist soil, the surface should be damp, if the plant needs average moisture, let the top inch dry out. Succulents prefer drier conditions. You can also gauge the wetness of the plant by lifting the container. If it feels light, the plant may need water.
Overwatering is a common cause of houseplant death. Be sure that the pot has a drainage hole. Do not let the plant sit in water. Overwatering can cause root rot, a fungal disease that makes roots unable to draw up water and nutrients. Healthy roots are light colored, roots affected by root rot are dark and mushy. Ironically, wilted leaves can be a symptom of both underwatering and overwatering. A wilted plant that doesn’t revive with watering probably has root rot and should be discarded.
Plants should be fertilized spring through fall. A general rule is to dilute the fertilizer to half the label rate and apply every two weeks. Do not fertilize a dry plant. Wait to begin fertilizing a newly purchased or transplanted plant for one month. White residue on the pot may indicate a buildup of fertilizer salts, which can harm plants. About once a month, scrape the residue off the top of the soil. Water the plant until water runs out the drainage hole to flush out salts.
Common houseplant pests include aphids, mealy bugs, spider mites, whiteflies, scale insects, fungus gnats and thrips. It is important to identify the pest before attempting to treat it. One symptom of aphids is shiny honeydew (insect waste) spots on leaves. Mealy bugs appear like white cottony blobs. Fine spiderwebbing on the underside of leaves can indicate spider mites. For assistance identifying pests or other plant problems, call the Minnesota Landscape Arboretum’s Yard and Garden Line 612-301-7590. The University of Minnesota Extension website, extension.umn.edu/garden/ , has an excellent resource, “Houseplant Insect Control,” that includes insect photographs and descriptions. It details both nonchemical and chemical treatments for pests.
With good care, your houseplants will reward you by beautifying and cleaning the air of your indoor environment. Nurture them!
This article was written by Julie Gordon, Master Gardener, U of M Extension Service, Hennepin County