Observing the growth and changes in your tropical plants allows you to determine if they are receiving enough light. Plants that don’t get enough light will usually look pale, have longer than normal stems, and smaller than normal leaves. Sometimes, a plant will look as if it is reaching for light: A sure sign that it needs to either be placed in a sunnier window or the natural light augmented with artificial light. Plants with colourful foliage will often lose colour when they do not get enough light and revert to green leaves.
Plants that are receiving too much light often develop burn spots on the leaves. In some cases, the leaves will turn pale and watery before wilting and drying up. These symptoms can have other causes, but if a plant is sitting in the hot sun on a south-facing windowsill when these symptoms occur, it is a good bet that too much light is the problem. Move it away from the window at least during mid-day, and give it a couple of weeks to determine if that makes a difference. Note that a south-facing window will produce less than 200-foot candles of light in winter and more than 2,000-foot candles in early summer. A plant that is happy in a sunny window this time year may not be so happy come summer.
Fertilizing indoor plants in winter is necessary only when you see new growth developing, or the plant is in bloom. Otherwise, your tropical plants are “resting” this time of year and will not benefit from a fertilizer application. It is best to err on the side of caution and give plants a little less than the amount the instructions call for.
There are several forms of fertilizer available: Granular, slow-release granules and spikes, and water-soluble. In our opinion, the best choice for houseplants is a water-soluble formula. The elements in it are readily available for the plant’s use and you will be able to see the effect right away. Choose from synthetic plant food such as 20-20-20 or an organic such as Pro Mix Liquid plant food.
The final step in choosing your houseplant fertilizer is determined by the plants you have. Some, such as African violets and geraniums, have fertilizers formulated specifically for them. African violet fertilizer, for instance, often is a 10-30-30 with traces of boron, copper, iron, manganese, molybdenum and zinc.
Do not fertilize plants when they are wilted, dry or dormant – in other words, not growing.
At this time of year, the air in most Canadian homes is very dry and conditions are perfect for insects to thrive. To raise the humidity around your plants, place a tray filled with pebbles and water under your plants. The water should not touch the bottom of the pots. The pebble/tray will create a humid atmosphere due to evaporation.
Keep the leaves free from dust accumulation by washing them with a soft cloth that has been sprayed with insecticidal soap. African violets and other “hairy” leafed plants should not be misted or washed with a cloth. They should be washed in lukewarm, soapy water. Just hold the soil in place with your fingers while inverting the plant, swish the plant in the soapy water and rinse twice in clear water.
Here in Canada, we endure a long, cold winter that encourages us to reach for tropical plants for good reason. There is literally no better way to introduce humidity and oxygen into the indoor environment. With the right care and located in the right place, your indoor plants will live a good long life and you will reap many benefits from them.
Mark Cullen is a Member of the Order of Canada. He reaches more than two million Canadians with his gardening/environment messages every week. Ben Cullen is a professional gardener with a keen interest in food gardening and the environment. You can follow both Mark and Ben on Twitter (@MarkCullen4), Facebook ( facebook.com/MarkCullenGardening ) and Instagram ( instagram.com/markcullengardening ). Receive their free monthly newsletter at markcullen.com .