Question:

I have a potted gardenia. How do I take care of it?

- F. McVeigh
Answer: Very attentively.

Gardenias, with their beguiling scent, are the dickens to carry over indoors in the winter. Many an expert gardener has met with failure when it comes to gardenias. (I know better than to try in my dry house.)

The most important considerations - and all the published advice I've read stresses that these are essential, inflexible requirements - are potting medium, proper irrigation, humidity, light, and temperature. In short, you must transform the room where you keep the gardenia into the equivalent of southern Japan.

The potting medium must be porous yet water retentive, as well as acidic (pH of 5.0 to 5.5 is one published recommendation). If your plant was recently acquired from a reputable concern, the medium should be OK. When the time comes for repotting (due to growth or hideousness of original container), try to find a houseplant medium formulated for acid-lovers. (Or amend regular potting soil with peat moss and perlite.)

Gardenias must not be allowed to dry out and must not be overwatered. The top of the planting medium should look and feel dampish. The pot should never sit in water, so place a thick layer of gravel in a tray, allowing drainage of the porous medium without creating a waterlogged situation.

Humidity must be high, and that's hard indoors in winter. Misting the plant will not be as effective as you'd wish - the room needs to be humid. Some people use humidifiers. Bathrooms are typically the most humid room of the house, but rarely are they light enough.

Give a gardenia abundant indirect light. Direct light from a south-facing window will be too much unless you hang a sheer curtain to diffuse the light. From late November to late January, the sun is so low on the horizon that fluorescent grow lights may be needed (place them close to the gardenia).

Gardenias prefer daytime temperatures of 70 and require night temperatures below 62. Sudden changes - such as a blast of cold air from an opened door - are bad news.

The process of transferring a gardenia from indoors to the garden, or the reverse, should be undertaken over several days, starting with an hour in the new environment, increasing an hour each day.

Q: I received a lemon tree, with fruit already, a year ago. It has never bloomed since. I kept it outside in summer, now in my sun room. It looks healthy but does not seem to be growing.

A: Let's hope your gift was a Meyer lemon, which is widely considered the best for indoor culture, especially the "improved dwarf" strain. Lemon trees take as much light as you can give them, though in a sun room in late spring you should not let it get too hot.

I suspect your tree was induced to bloom heavily and set fruit, possibly out of season. After that, like an azalea that was on drugs, so to speak, it needed to rest and thus did not bloom last summer. If it looks healthy now, let's assume that it has settled down from the induced performance, is undergoing a typical winter low-growth period, and will get into the normal swing of things this summer.

Sue Williams, a Penn State master gardener in Adams County, encourages Northern lemon growers to provide five to six hours of sunlight a day, supplemented by lights if necessary. An acidic fertilizer can be applied for the active growing season, in March, June and August. (Citrus formulations are also available; it may be easiest to phone a friend in Florida to go to a garden center there.)

Good drainage is needed, and the top of the soil should be allowed to dry out a bit between waterings. And, surprise, surprise, conditions more humid than the typical heated house are recommended.

Send questions to Michael Martin Mills, The Inquirer, Box 41705, Philadelphia, Pa. 19101 or gardenqanda@earthlink.net. Please include locale. Read his recent work at http://go.philly.com/michaelmartin

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