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 our indoor environment. To garden indoors successfully, especially this time of year, it's important to provide the best possible growing conditions. With the right care and location, your indoor plants will live a good long life and you will reap many benefits from them.
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's reaching for light, stretching its leaves and lengthening the distance between growth nodes toward the nearest window – a sure sign that it needs either to be placed in a sunnier window or the natural light augmented with artificial light. Plants with colourful foliage will often lose colour when they don't get enough light, and revert to green leaves. It is natural for most flowering plants to stop flowering through the winter months.
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's 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, spikes and water soluble. These can be organic or inorganic chemical combinations. In our opinion, the best choice for houseplants is an inorganic, 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.
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 ratio with traces of boron, copper, iron, manganese, molybdenum and zinc.
If there is no specific formula for your houseplant, a 20-20-20 ratio with trace elements is best.
Rules of fertilizing
We follow three rules for successful fertilizing:
Do not fertilize plants when: They are wilted, dry or dormant. Plants need nutrients only when they are actively growing or flowering. Fertilizing at other times could cause a build-up of insoluble salts in the soil, which can damage the roots. If white salts build up on the pot rim or soil surface, stop fertilizing and drench the soil a couple of times with generous doses of water (putting them in the shower works!) then, if growth continues, resume feeding in a month or so, using less fertilizer. If the plant stops growing or wilts, despite the proper watering schedule, stop fertilizing, and drench again. Then wait until growth resumes before starting up the fertilizing and use a weaker solution than before.
In the winter months, the air in most Canadian homes is 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 them. The water should not touch the bottom of the pots. This will create a cooler, humid atmosphere due to evaporation. Routinely inspecting houseplants enables you to observe and correct most problems before they get out of control. You will be able to spot insect or disease problems before they get too serious. 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, but instead 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.