by Marg Fleming
1979 - BSc. Botany University of Toronto, 1981 - MSc. Forestry University of Toronto, 1982-1986 - Horticulture Teaching Master - Niagara College , St. Catherines Ontario., 1986 - 2000 - Owner/Operator of Cedar Valley Botanical Gardens - Brighton Ontario, 2000- Present - Manager of Horticulture Toronto Zoo
Public Speaking Topics - Perennials, house plants, garden design
At this time of year the focus of a gardener’s attention turns inside to the welfare of tropical plants. Our indoor plants look out on a snow-covered landscape while basking in the warmth of our winter homes. But houseplants encouraged to survive until spring require more than just tropical temperatures. Proper humidity, light, air circulation, and pest control all combine with moderate temperatures for successful indoor plant culture during our extended winter. Here are a few basic tips for some of our most commonly kept houseplants.
Humidity is important for plants in winter. Our dry homes provide little of it, but levels can be raised for our own comfort and for the welfare of houseplants. An inexpensive humidifier is likely the easiest solution. Alternatively, strategically placed shallow pans of water situated close to heat sources can emit their vapours over time. But these require frequent refilling and a constant adequate level of humidity from this technique alone is difficult to achieve. However, individual humidity-craving plants such as epiphytic orchids and bromeliads can benefit from a slight modification of this tactic. By placing coarse gravel or rounded stones into the shallow pan or dish, a humidity-loving potted plant can be placed on top. The plant on its gravel-filled pan can then be situated on a heat source and the pan filled with water to a level just below the top of the stones. The warmth from the heat source (radiator, warm air vent) will assist in evaporating the water from the pan. By keeping the water level in the pan below the top of the gravel, the potted plant on top will escape wet feet while basking in the humidity that engulfs it from beneath.
Admittedly this technique is dependent on having the heat source in close proximity to adequate light, and most modern homes have eliminated bulky radiators. Nevertheless the concept can be kept in mind and adapted to individual situations whenever possible.
Even though houseplants are in a state of dormancy during the winter, their existing leaves and stems still require light to keep them alive. Winter sunlight is of poorer quality than that to which the plant has grown accustomed during the summer, so it may be wise to provide supplementary light. Move plants closer to the window or pull back sheer drapes during the most intense part of the day. South windows are best in winter. They provide the most direct, quality light for the longest time.
There is a limit to what we can do at this time of year to improve the light that our plants see. We can maximize the availability of what exists, but remember that the shortest day of the year is still 3 weeks away. Before any substantial improvement in light quality and quantity, we must endure the dim month of January. Anything we can do to provide better light conditions for our houseplants will help to sustain them through this time. In February plants will suddenly sense a change in day length and growth will begin once again.
Heat in the winter home is extremely variable. Thermostats are located away from exterior walls where they would be able to sense cold air from outside. So plants located near windows are liable to get rather cool before the thermostat engages the furnace. These same plants could experience quite an increase in temperature before the furnace is signaled to turn off. Some plants enjoy this temperature flux. Others will suffer.
Most plants enjoy a change in temperature between daytime and nighttime temperatures. The degree of change tolerated depends on the nativity of the plant. Tropicals will obviously tolerate less of a difference between day and night temperatures than temperate plants. We turn down the thermostat when we retire for the night. Plants sense this the same as they would in their natural environment. Where daytime temperatures may have reached 72 degrees F, nights could dip to 65 F. Some plants will thrive, others may suffer.
So briefly we have investigated the variation we experience in our homes regarding heat, light, and humidity. Different plants tolerate different levels of these factors as they yo-yo day by day, and morning to evening. Purchase a comprehensive book on houseplants to determine different species’ likes and dislikes. It will help you to select the appropriate place in your home for minimizing the stress these factors have on your indoor plants.