Lush, green houseplants can help brighten our spirits on cold, winter days. Besides adding beauty and being an integral part of interior decoration, houseplants help satisfy the gardening urge for people who can‘t have outdoor gardens or who can’t wait for the start of next year’s outdoor growing season. And, research shows that plants help clean indoor air and have therapeutic effects for people of all ages. Indoor gardening can be very simple, or as challenging as the most dedicated gardener desires.
Because we are located so far north, we have drastic seasonal fluctuations not only in temperatures, but in the duration and intensity of daylight. To keep houseplants healthy, consider light, temperature, water, humidity and nutrient requirements, all of which are interrelated.
Start by choosing plants that are adapted to your home environment and the amount of light you have. All plants need light to conduct photosynthesis, which creates the food (carbohydrates) needed by the plant to grow. In winter, we have fewer hours of daylight and the sun’s low angle causes winter light to be less intense. Add to that the fact that we have more cloudy days in winter, and light becomes the most limiting factor to healthy plant growth indoors. These low light levels cause most plants to go into a period of low activity, with little if any growth.
If you’ve summered your houseplants outside on your deck or patio and brought them back in for winter, be prepared for some initial leaf drop. Even if your plants are in the shade outside, the light is still brighter than it is inside most houses. Once brought indoors, some plants will shed their summer leaves and grow new leaves that are thinner and more able to survive in lower light levels.
Consider ways to maximize light levels for indoor plants over winter. South windows will have the highest intensity, so you can move houseplants to those areas, but beware that in March and April, leaves may scorch as the sun becomes more intense. Remove window screens in winter, as they block an amazing amount of light. And, wash your windows!!! Dirt on windows also blocks light. Finally, consider adding supplemental light. A simple fluorescent light positioned a foot or two above a houseplant and left on late into the evening can be extremely beneficial.
The amount of water a houseplant needs is dependent on the amount of light the plant receives, the humidity, the potting soil mix, and the room temperature. A plant growing actively in good light will need more moisture than one growing slowly in minimal light. Higher temperatures and lower humidity also increase the need for water. Don’t water on a schedule—water only when the plant needs it. Dig your finger into the surface of the soil and if it’s dry ½ inch deep, it’s time to water. Sometimes it will take 4 days to become dry, and other times it will take 10 days. More houseplants die from overwatering, which suffocates roots and allows root rot fungi to set in, than from underwatering. Plants usually develop brown leaf tips, when soil is allowed to get too dry. Always water thoroughly until water comes through the pot’s drain holes, but do not let the plant sit in a saucer full of water.
Temperature is another consideration that affects the happiness of your houseplants. Most plants prefer days between 65 and 75 degrees F, with nights about 10 degrees cooler. The more light a plant has, the higher temperatures it can tolerate. High temperatures and low light produce spindly, weak plants. In most cases, flowers will last longer on plants if kept in cooler conditions, with temperatures in the 60’s.
Keep plants out of cold, drafty locations such as entryways where cold air blasts the plant when doors are opened. Also avoid hot, dry areas such as near heat vents.
The indoor heating season results in our homes usually being quite dry. Low humidity increases the amount of moisture lost through houseplant leaves, which may increase the amount of watering necessary. Using room humidifiers and grouping plants together can increase humidity. Setting pots above (not in) a tray of water also increases surrounding humidity. Misting plants raises humidity for only a very short time.
Be careful not to over-fertilize your houseplants during winter in an attempt to encourage growth. Plants manufacture their own food during photosynthesis, and use fertilizer as a “vitamin” supplement. During the winter, when light levels are low and photosynthesis slows, plants won’t do much growing and therefore have no need for fertilizer. Wait until late February or March to fertilize, when increased light levels cause plants to increase growth. Always mix fertilizers at ½ the rate recommended on the label. Fertilizers can easily build up in houseplant containers and cause browned leaf tips and burned roots. This can result in stunted growth, or root rot fungi can move in and cause plant death.
Give your plants an occasional shower or sponge bath during winter. Dust builds up on houseplants and blocks the already low light from reaching the leaves, reducing photosynthesis even more. Large plants can be placed under the shower for a few minutes to wash dust and dirt off leaves. Place tinfoil over the pot to keep soil from splashing out. Smaller plants can be treated the same way in your kitchen sink, using the hand sprayer or a spray bottle.
Keep a close eye out for insect pests indoors, especially spider mites and mealy bugs, and treat accordingly. Spider mites love the warm, dry indoor air and can get out of hand quickly and do a lot of damage by sucking the juices out of the plants.
When winter’s over, you will be anxious to get back outside, and so will your houseplants! Summering them in a protected outdoor spot will invigorate them and improve their lush, full appearance.
For questions or more information about caring for your plants, contact Diana Alfuth, UW-Extension Horticulture Educator, at the Pierce County UW-Extension office, (715) 273-6781.