No, I don’t grow gardenias (Gardenia jasminoides, syn. G. augusta et G. grandiflora), sometimes called crape jasmine or cape jessamine. Not that I haven’t tried. After all, their large, heavenly scented white flowers fading to cream are drop-dead gorgeous! And the better clones will rebloom throughout much of the spring and summer.
However, my repeated failures have taught me growing gardenias under my conditions is a waste of time and money. And that might apply to you too.
Grow Them Outdoors… If You Can
Gardenias come from Southern China and other mild climate areas in Asia. The plant is essentially a subtropical shrub with shiny evergreen leaves found at moderate to high elevations where it gets a combination of frost-free growing conditions and cool temperatures. It will tolerate short periods of light frost and will grow in USDA hardiness zones 8 to 11, possibly zone 7 if well protected or if you choose an extra-hardy clone like ‘Kleim’s Hardy’ or ‘Frostproof’. It makes a much better and more floriferous outdoor shrub than a houseplant!
Where gardenias can be successfully grown, they probably already are. So the first clue to their “growability” is to ask a local master gardener or garden club member. If they say it can’t be grown, it’s probably true.
Gardenias need even moisture throughout the year and prefer a rich and slightly to moderately acid soil (a pH of about 5.0 to 6.5). They also need good atmospheric humidity, plus cool temperatures in late winter and early spring for bud set. However, if it gets too cold, they won’t bloom … and frost as the buds form is definitely a no-no! They like full sun, but hate intense heat. In many climates, you’ll need to plant them where they get shade from the midday sun.
Note all those limiting factors: this plant can be persnickety indeed!
Given that I live in USDA zone 3 (AgCan zone 4), I’m nowhere near to being able to grow this plant outdoors.
Growing Gardenias Indoors
Gardenias are easy to grow in a cool greenhouse—after all, such structures offer full sun, cool conditions and high atmospheric humidity, exactly what the plant wants—and that’s why they show up so often in the spring or early summer in garden centers, always in full bud or bloom. Nurseries can produce them readily and cheaply and they’ll “hold” in stores for a week or so, hopefully until they’re sold. Eager gardeners then bring then home … and then the buds promptly fall off. Did I mention gardenias don’t like being moved when in bud or bloom, especially if the air is dry? Bummer!
Most people just don’t have the right conditions to grow gardenias—or at least get them to flower—indoors. Our homes are simply too hot and too dry in the winter. But if you can supply cool night temperatures—about 60–65˚ F (15–18˚ C) and day temperatures that are fairly moderate, not much about 70˚ F (21˚ C), plus high humidity at all times, you can get them to bloom. You’ll note that the description of the proper conditions more closely corresponds to those of a cool greenhouse than the average living room. Exactly!
If you can offer those conditions, go ahead! Once you get the cool temperatures, humid atmosphere and intense light (they prefer full sun indoors in winter, but some shade during hotter months) they need worked out, basically all you need to do is water them—preferably with rainwater, as they don’t like the hard water that comes out of most faucets—and fertilize them occasionally with just about any fertilizer (some people prefer fertilizer for acid-loving plants, but they aren’t really necessary if you use rainwater). Prune, after blooming, if they get too big.
Piece of cake … well, maybe for you!
I can give my houseplants high humidity and bright light, but I just don’t have the temperature control I’d need to keep gardenias happy during that critical period in late winter/early spring when they bud up. I can offer too hot (anywhere in my house) and too cold (a cold frame that freezes regularly), but nothing in between.
And that’s why I don’t grow gardenias.