Caring for houseplants in northern climates
Although many books have been written about caring for houseplants, few address the particulars of plant care in northern climates. Living this far north, we experience vast seasonal fluctuations, not only in temperatures, but in the intensity and duration of daylight. Because light, water, temperature, humidity, and nutrient requirements of houseplants are all interrelated, we must take these changes into consideration to keep houseplants healthy year round.
Light is the most limiting factor to good houseplant growth indoors. All plants need light for photosynthesis, the creation of food energy essential to maintaining life processes and growth. Without sufficient light, plants will develop weak, spindly growth, and will be more vulnerable to a host of other problems.
Houseplants must be placed where light is bright enough to sustain growth.
A vigorously growing plant is not only easier to keep healthy, it's more attractive. The amount of light needed varies from one plant to another. Check a reputable reference, then select plants to fit the available light in your specific indoor locations.
In northern latitudes, we change from long hours of daylight in spring and summer to much shorter days in fall and winter. Due to the sun's angle, winter light is less intense; weather is often cloudier, too. Houseplants may grow better if you move them into brighter windows or nearer to windows so they may receive as much light as possible. Be careful not to place them close enough to be injured by cold; never allow foliage to actually touch window panes.
Houseplants that were fine in a south or west-facing window all winter may sunburn there in late spring or summer. Sheer white curtains can protect against heat and burning sun while allowing adequate amounts of light through to the plants. Or you can move plants back from the brightest, hottest locations. Disregard care tags that tell you to keep houseplants out of direct sunlight, however. Most will benefit from an hour or two of direct light each day, so long as it's not too hot.
Everyone knows houseplants demand regular watering, but how often they should be watered depends on many factors. Water requirements vary according to the size and type of houseplant, the container, and the potting medium. Environmental conditions such as light, heat, and humidity also affect a plant's water needs. A houseplant growing actively in good light needs more moisture than one growing slowly in minimal light. Higher temperatures and lower humidity also increase the need for water.
Always water thoroughly until water comes through the pot's drain holes. Discard excess water that collects in the saucer. Learn to recognize when the plant needs water by feeling the soil. Some plants such as ferns and African violets need water as soon as the soil surface feels dry. The potting medium of many cacti and succulents must dry thoroughly before watering. For most houseplants, allow soil to dry ½ inch or more below the surface, depending on pot size. Water when conditions warrant, not automatically on a rigid schedule.
Plants that don't need to dry a lot may thrive in "self-watering" containers that make use of reservoirs for sub-irrigation. These containers save time and labor, and can result in excellent growth due to the even supply of moisture they provide.
Optimal temperature ranges vary somewhat among different houseplants. However, most prefer days between 65 and 75 degrees F, with a drop of 10 degrees at night. Plants grown under slightly cooler conditions are more tolerant of lower light intensity than those grown at higher temperatures. Cooler temperatures also reduce the amount of moisture lost from leaf surfaces through transpiration.
Keep houseplants out of cold, drafty locations such as an entryway in winter or near an air-conditioner in summer. Try also to avoid hot, dry spots close to radiators or heat ducts in winter. As long as air is neither excessively hot nor cold, good air circulation, as provided by a ceiling fan or forced air register some distance from the plants, is beneficial.
Many houseplant species originated in tropical rainforests and areas of high humidity, but our homes are usually quite dry once we start heating in fall. Low humidity increases the amount of moisture lost through houseplant leaves, which means you must be careful to water as often as necessary. Plants may develop brown leaf tips when soil is allowed to dry excessively.
Increasing relative humidity helps slow moisture loss and discourages damaging mites and insects that thrive in warm, dry conditions. Don't mist your plants; it raises humidity only momentarily, but in the process sets the stage for fungal and bacterial leaf spot diseases. Instead, use room humidifiers and group plants together to benefit from moisture they lose through transpiration. You can also place plants on supports in trays of water so that it evaporates around them, but doesn't wick up through the bottoms of their containers.
People often over-fertilize houseplants in an attempt to encourage vigorous growth. Plants manufacture their own food through photosynthesis, and need fertilizer only as a supplement. Plan to fertilize when plants grow actively, usually spring and summer's longer days. Then reduce or eliminate fertilization the rest of the year. Plants growing under fluorescent lights won't experience a seasonal change in light, so they might need fertilizer applications year-round.
Always mix fertilizer ½ the label recommended strength. It's easier to repeat an application than to deal with the potential consequences of excess fertilizer--brown leaf tips and margins and burned roots, followed by stunted growth and ultimately, plant death.
There are many houseplant fertilizers on the market. Almost any will do, provided you tailor label recommendations to the time of year and your plants' needs. Never fertilize a plant in dry soil. Instead, water the plant over a sink or washtub, then water a second time with fertilizer solution.
Dust and grime build-up is unattractive and encourages insect pests. It also filters the light that ultimately reaches leaf tissue for photosynthesis, so it's particularly important to keep leaves clean in winter, when light is at a premium. Clean large leaves individually with a soft rag moistened in lukewarm water containing a few drops of mild dishwashing soap. Plants with lots of tiny leaves may be turned upside down and swished through a tub of similar water.
Plant shine products often provide a stickier surface on which dust and dirt may cling. A shiny surface also reflects light away from leaves, where it is needed for photosynthesis.
Most houseplants benefit from spending summer out-of-doors, but you must find suitable locations for them. They can take direct sunlight early mornings and late afternoons when the sun is low in the sky, but they must be protected from hot, intense sunlight the rest of the day. The north side of your house is usually a good choice; so is any area shaded by a large tree.
Warm temperatures and drying breezes mean frequent watering outdoors. Increased light results in added growth and the need for regular fertilization. It may also indicate the need to repot plants in larger containers several weeks before bringing them indoors.
Put houseplants outside in early summer when night temperatures begin to approximate those indoors. Take them in when night temperatures cool in late summer or early fall. Don't wait till frost threatens; the transition from such cold nights to indoor conditions will prove difficult.
Inspect your plants and wash them carefully before bringing them into the house. Spray only if insect pests are present. Once indoors, place plants in your brightest possible windows for several weeks before moving them to their original locations.
The following publications will give you additional information about houseplants:
|"Cacti and Succulents"
"Forcing Bulbs for Indoor Beauty"
"Outdoor/Indoor Geranium Culture"