Regularly offered as a gift plant, especially during the winter season, the florist’s azalea (Rhododendron simsii) also makes an excellent indoor plant that can bloom abundantly from year to year, each session lasting weeks, if not months. Make no bones about it: this is a demanding plant, not something I’d recommend to a novice indoor gardener, but it is possible to keep it alive and well for many years if you are very careful.
This subtropical plant needs a bright and cool location with some direct sun during the winter and also fairly good air humidity. During the summer, though, you should seriously consider moving this plant outdoors to a shady spot. There are several reasons for this move, but one of the most important is that the florist’s azalea isn’t terribly tolerant of tap water. Whether it is from a well or a municipal system, tap water tends to be hard (rich in calcium) and azaleas are intolerant of calcium. They like acid soil and soft water. After a winter indoors, it will therefore very much appreciate rainwater as it is calcium-free and in fact generally fairly acid. Repeated rains over the summer will help leach the plant’s soil of excess calcium, making your plant very happy. In areas where summer rains are infrequent, it’s probably best to either store up winter rainwater for summer use or to water your azalea year round with distilled water.
Fertilizing this plant is also tricky, for the same reason: most fertilizers are rich in calcium. Fertilizers for acid-loving plants (often labelled “Azalea and Rhododendron Fertilizer”) do exist, but conventional all-purpose fertilizers can also be used as long as you dilute them to 1/4 of the recommended rate… and let Mother Nature leach the soil of excess calcium during the summer.
Leave your azalea outdoors until well into the autumn, because flowering is induced by several weeks of cool temperatures (between 4 and 13 ° C). In my area, where frost comes very early, I still leave my azaleas outdoors until late fall, but bring them indoors on frosty nights, then put them back outside the next morning if it warms up. As the cool treatment progresses, you’ll see plump flower buds form on the ends of the branches, a sure sign you’re doing everything right.
You’ll usually find that your home-grown florist’s azalea will not be totally covered in blooms the way commercial “straight from the greenhouse” azaleas are, but rather will produce clusters of blooms starting shortly after you bring them indoors and continuing right through until spring, thus giving a much longer show than you had the first year. Personally, I prefer 4 months of moderate bloom to 3 weeks of intense bloom. Don’t you?
Finally, one final tip: inside or outside, in warm weather or cool, make sure your azalea never lacks water. With its extremely fine roots absorbing every drop you pour and its abundance of small leaves and flowers that transpire massively, its potting mix can dry out very rapidly. So, especially when it is in bloom, you need to check your azalea at least twice a week, watering as soon as the soil feels dry to the touch.