If you haven't begun the annual ritual of tampering with the lifestyle of your Christmas cactus to get it to set flower buds, you really need to get going. Or, if you're like me and left it outdoors until the freezing temperatures of last week, you still need a trick or two to ensure the buds will set. Remember, for certain plants, we need to fool Mother Nature for them to perform desired feats. To get a poinsettia to flower, we ensure uninterrupted darkness every day for 10 straight weeks beginning Oct. 1. Easter lilies require an extended period of cold. Growers have perfected interceding on Mother Nature's behalf with these plants. The Christmas cactus, Schlumbergera bridgesii, needs both controlled light and a cool temperature for flowering, both of which we as home gardeners can provide rather easily. The best way to understand this plant's cultural needs for flowering is to learn about its natural lifestyle so we can imitate Mother Nature, too. This cactus is native to the Organ Mountains just north of Rio de Janeiro, Brazil, which rise above 7,000 feet. It naturally blooms during the month of December, hence its name. The forest it grows in on these mountains is a tropical one, providing much-needed humidity throughout most of the year. The tree line climbs to elevations of 5,000 feet, where the temperatures are much cooler than at sea level and the rainfall is more moderate. The cactus itself lives high in the canopy of these trees, where dappled shade, cool temperatures, humid conditions and limited rainfall exist. It roots itself in the decomposing leaf debris that has been captured in the nooks and crannies of the tree's trunk and limbs. Knowing all of this gives us a good insight on the Christmas cacti's cultural requirements. It thrives in moisture-retentive leaf debris in nature, so moisture-holding potting mix -- not the highly draining sand a typical desert cactus prefers -- works best. It prefers humidity because it grows in a tropical forest. So dry air, especially when in the bud stage, must be avoided. So run a humidifier, place a tray filled with stones and water underneath the plant, or find some other way to ensure more rather than less humidity during the winter heating season. If you've encountered bud drop in the past, lack of humidity is often to blame. This is not a true cactus, and because it naturally lives in that tropical forest, it requires more water than you might expect. Water thoroughly so the excess drains out the bottom holes. Then promptly empty the saucer; never allow the plant to sit in water. Allow the top inch of soil to dry in between watering. This plant will wilt and look dull if it is too dry. It's important that it gets sufficient water year-round, as drought is not tolerated. Now to the bud-forcing process. It lives in the coolness of higher altitudes, so during bud formation, heat is not its friend. If you've had it outdoors until last week, you've met the low-temperature requirement. If not, you need to move the plant to a cooler room that hovers around 62 degrees to 65 degrees all day and night. Typically, cold treatment begins in early October. This date is late, but you can still pull a bloom off; it will just be delayed. It lives under the heavy canopy of trees, in the naturally decreasing daylight hours as winter approaches, and where no artificial lighting occurs. So move your plant into a cool room where it remains dark after nightfall and there is no on-and-off of artificial lights. Even if you had your plant outdoors and can feel no bud formation at the tips of the leaf segments at this time, I would continue the dark and cold treatment for a few more weeks, checking for buds periodically. Once the buds form and begin to show color, move your cactus to a spot where you can enjoy it. For some folks, the year-round conditions the plant prefers don't require any tampering. They're perfect just the way they are. Take my friend Lorie. She has a huge Christmas cactus. She couldn't budge it if she wanted to in the bay window of her beauty shop. The window provides the coolness needed, the shop gives it loads of humidity, and when Lorie closes up at night, the lights stay off. This plant is absolutely loaded with buds. You've really got to see it to believe it; it's amazing. Her shop mimics all of the necessary natural conditions required. She needs to do nothing. Understanding the whys of nature helps us to understand the hows of nature, and the plant world is loaded with both! (Nancy O'Donnell owns Perennial Graphics Nursery in Schaghticoke, N.Y. Contact her by e-mail at dodonnell@nycap.rr.com. Gardener's Notebook can be found at http://timesunion.com/life.) 