Many of us gave our houseplants a vacation all summer long to recharge and recover from being indoors, yet here we are again dealing with them for the dark days of winter.

It is absolutely true that they need to be watered and maybe even occasional fed, but the most important piece to keep them going until spring is light. Unless you have that sunroom with windows all around, keeping up on the light requirement can be hard to do for every kind of houseplant we have.

You know something is up when the houseplants begin to have small leaves and long thin stems reaching for more light. Older leaves may begin to yellow and drop, and in general, your plants may be looking weak.

Light levels

Different houseplants require different light levels, which means the location in your home makes a difference. Low light levels (sometimes referred to as 75 foot-candles) come from not getting any direct light, such as a north window or being 8 feet or more away from any other light source. East- or west-facing windows give us a medium level of light (or about 150 foot-candles), which is also like being about 5 feet away from a southern window. The winner of the foot-candle race is a south-facing window, giving bright light at about 300 foot-candles. Natural light is the best even if one sided coming in from the window. To prevent one sided growth, rotate the plants to keep growth even.

More light factors

Besides the need for light in general, there are three other conditions to consider – duration, quality, and intensity.

• Duration is how long the plants receive light.
• Quality is about the wavelengths in the light.
• Intensity is the strength of light the plants receive.

Houseplants you are trying to bloom need the correct amount of each in order to bloom. Foliage plants can be acclimated to lower levels of each and still look good.

Sources of supplemental light

If you want to supplement your light or use non-natural light, fluorescent was the best option for many years, but now we have a new player on the block, LED.

Fluorescent tubes can be purchased to have improved quality of light as “grow bulbs” or “grow lights,” and fit the standard 48-inch fixture. Cool white and warm white bulbs add to both the duration and intensity by how long the fixture is on and how close the foliage and the tubes are. Fluorescent fixtures do generate heat so that can be a concern.

LEDs can be found with light that satisfies the quality and intensity issue without the heat factor. LEDs designed for plant growth will give us an interesting “glow” and the plants and any flowers will not look “natural” with the lights on, yet they will be a lot healthier.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.