Imagine a plant that flowers only once or twice a year, always at night, and sometimes flowers so quickly that people in the house never know the plant has flowered. Such is the unique behavior of the nigh-blooming cereus, a semi-tropical plant that’s unknown to most gardeners across the nation. Of all plants, cereus traditionally has the least following.

First, there aren’t many cereus in the horticultural world. Those that flower during darkness are as follows:

* Honolulu Queen: the plant produces 12-to-14-inch diameter flowers on stalks running 5 to 6 feet tall.

* Queen of the Night: this hybrid produces 12-inch wide flowers.

* Other flowering cereus include Moon Cereus and Moon Goddess.

Here is the year-round care program for the cereus:

March. In the first week of the month, prune the stalks back severely to within 6 inches of the pot. The reason: cereus flowers only on new wood grown from spring onward. Next, improve the soil. Using tepid water, water the plant thoroughly in the sink, then spoon off the top inch or two of old soil. Replace this with Pro-Mix Potting and Seeding Soil that you will find at the nursery (an 8-quart package sells around $4). Add some soil to a plastic dishpan in the sink, then hot water to wet the soil in seconds. Spoon this onto sheets of newspaper, scratching in a teaspoon of 0-5-0 bone meal and a teaspoon of pulverized lime. Having mixed these ingredients in the pre-wet soil, spoon this into the top few inches of the pot. Add more warm water to remove the air pockets. Now, set the pot in strong indirect sunlight near a south or west window. From then on, keep the soil lightly moist. To know when to water, rest a finger atop the soil in the morning. When you sense the soil starting to dry, add tepid water right away; let the pot drain fully, then return to the window location. Fertilize once a month with Jack’s Classic 15-30-15 Houseplant Special at the rate spelled out on the label. Stop plant food after late September.

SPRING. Continue your care program: the cereus stays in bright indirect light…keeping the soil lightly moist…fertilizing every four weeks.

SUMMER. When daytime temperatures rise to the high 70’s or low 80’s, the cereus should be moved outdoors into full sun, otherwise partial shade. The vertical stalks must be anchored onto a trellis or fence, otherwise the vines will sprawl and create a mess. If the plant is in sunlight, be sure to check for soil moisture every other morning; the cereus may have to be watered every morning, maybe again in the evening. Fertilize every four weeks with 15-30-15. It’s the nighttime humidity enveloping the cereus that triggers subsequent flowering.

If you want to forecast when the flowers will happen, check the calendar for when the next “new moon” will occur. You can expect the first flower within 48 hours after the new moon. With this flowering sequence, the flower buds swell quickly. In the morning, buds may be 7 or 8 inches high, yet barely a few inches wide. By early afternoon, buds swell to about 5-inch diameter while the height of the bud is now almost 12 inches. Around 9 p.m., the flower will open and remain fully extended until minutes before sunrise the next morning, at which time the flower disintegrates. After this, resume monthly applications of Jack’s Classic 15-30-15 in hopes of producing more buds when the next “new moon” happens.

SEPTEMBER. Check your calendar to see when the next “new moon” should occur. After the new moon, your cereus may flower for the last time in the calendar year. A few days after the new moon, bug-proof the stalks and foliage by moving the plant into shade (a garage will do), then dousing the plant liberally with liquid Diazinon or Orthene. When the plant dries, move the cereus indoors to a south or west window. Keep the soil lightly moist through late September and most of October. Discontinue all plant food when the plant is moved indoors.

HALLOWEEN. In the first hours of November, allow the cereus to go semi-dormant. From here on, let the soil go dry an extra day or two, then add warm water. Cereus will take indirect light, so you need not leave it in a south or west window from early November onward. Infrequent watering is needed to keep the roots alive over the fall and winter, but invariably there is some dieback of the stalks (to be expected).