Often sold as holiday gifts at Christmas or Easter, kalanchoes (Kalanchoe spp.) naturally bloom during winter and spring. If you don't understand why your plant never flowered again after its first time, keep in mind that it must experience 12 to 14 hours of darkness every night for a six-week period to set buds**.** Flaming Katy (Kalanchoe blossfeldiana), the most widely sold flowering species, grows to 1 foot tall with clusters of small red, orange, pink, yellow or white blooms. It and other kalanchoes, hardy only in U.S. Department of Agriculture plant hardiness zones 10 through 12, are most often raised as houseplants.
Place the kalanchoe on a sunny south-facing windowsill during the winter. For the rest of the year, keep it on an east- or west-facing windowsill, where it receives sunlight only part of the day.
Water it thoroughly once a week – or whenever the surface of its soil feels dry during its growing season from April to September – using lukewarm water and emptying its plant saucer afterward. Feed the kalanchoe once a month during that time period, adding 14 drops of a 10-10-10 plant food to each 1 quart of water. From October through March, cease feeding the plant and reduce its watering to once every two weeks.
Give It a Rest
After the plant stops blooming, clean pruning shears with rubbing alcohol and snip off the withered flowers and the tips of any stems that have become lanky before moving the kalanchoe to a windowsill that receives no direct sun. In The House Plant Expert, D. G. Hessayon recommends you allow the plant to rest there, almost dry, for one month**.**
After its break, repot the kalanchoe in fresh soil and a pot one size larger than the last one. If you tend to over-water plants, select a clay pot with drainage holes and cactus potting soil. Otherwise, a general-purpose, quick-draining potting soil and any pot with drainage holes should suffice. Gradually return the plant to the sunny or partially sunny windowsill it occupied before its rest.
During the summer, move the kalanchoe outdoors to a position in bright shade. Julie Day of Today's Homeowner warns that you should set the plant under an overhang, such as a porch roof, as too much rainwater may cause its roots to rot**.** Continue to water and feed it as before until late September.
Back to Work
In early October, bring the plant indoors, and place it on an east or west-facing windowsill, where it receives partial sun. This windowsill should be in a seldom-used room, such as a guest room, which will remain dark after the sun sets each evening. Leave the kalanchoe in that room for six weeks, watering it once every two weeks. Dr. J. Raymond Kessler Jr. of Auburn University recommends that the plant be kept in a place where the temperature doesn't rise above 75 degrees Fahrenheit during this dark period nor fall below 62 degrees F. At other times of year, the plant will tolerate any temperatures between 60 and 85 degrees F.
If you don't have such a secluded room, place a box or dark cloth beside the kalanchoe and cover it at 5 p.m. every night at supper time, uncovering it when you breakfast at 7 a.m. Should your schedule be different than that mentioned, simply remember that the plant needs 12 to 14 hours of complete darkness every night for six weeks.
At the end of that time period, gradually move the budded plant to a south-facing windowsill for the winter. Depending on the cultivar, the plant may bloom at any point from two weeks to seven weeks after its dark period ends – that is, from early December to early January. The flowers should last from three to six weeks.