Q: My gardenia grows outdoors all summer, but the buds drop off when I bring it inside. How can I make it bloom indoors? — Garth Lundgren, Spokane, Wash.
A: Notoriously finicky about their accommodation, gardenias require more sun than most houseplants and are more inclined to bloom in spring than in fall. Flowers form only on new growth: each joint between leaf and stem has the potential to make a flower bud, but if a bud drops off, that joint will never produce another. Steady light, temperature (70º to 80ºF is ideal), moisture, and feeding are the keys to healthy growth — and abundant bloom. Indoors, a conservatory or greenhouse provides the best conditions, but a sunny window will do. If a potted gardenia has been outside, acclimate it to interior light and temperatures gradually. Grow it outdoors, in light shade, and in fall bring it indoors in the evening as soon as temperatures fall below 60ºF. After you have brought the gardenia inside, feed it regularly with an acid fertilizer, either a soluble mix or slow-release pellets (any formula for azaleas or evergreens is fine). Water the gardenia when the soil still feels damp, but do not keep it sopping wet. Continue this regimen indoors. Joy Logee Martin, of Logee’s, in Danielson, Connecticut, warns that the gardenias many garden centers and florists sell are potted in black soil that’s hard to test for moisture (it always feels damp). She advises transplanting the gardenia, in spring or early summer, into a houseplant potting mix containing peat moss.