A Thanksgiving cactus, which is the same genus (Schlumbergera) as a true Christmas cactus but a different species, has leaves with curved, pointed “teeth,” whereas the Christmas cactus has rounder leaves.

The recommended moisture reading may depend on the manufacturer of the meter. For Rapitest, for example, the recommended reading for a Christmas cactus is 6. So you would not water if the reading were any higher. If the number is the same or lower, you would water. Check every 4 or 5 days. During the dormant season, however, reduce watering. So, when the plant stops producing blooms, reduce the watering until flower buds start to appear again.

If the cactus is dropping its leaves, check that it has enough humidity (around 60 percent), and check that the water is draining out at the bottom. Waterlogged plants can lead to root rot, which can cause branches to fall off. Also make sure that the soil hasn’t become compacted (too dense); if it is, then you may want to repot the plant with fresh soil, but wait until after the plant has finished flowering, but before new flower buds form.

Hope this helps!

Overwatering is the likely culprit. Let the plant dry out a bit more between waterings. It could also be caused by too much direct sunlight. Keep it in a spot that gets bright but indirect light.

Unfortunately, Christmas cacti are not very tolerant of cold temperatures and extreme temperature changes, so yours may have a hard time recovering. The best you can do now is to keep it in a warm place with bright, indirect light and care for it normally. Make sure it is kept moist but not wet—overwatering can cause wilting, too. 

While you wait for the plant to recover, perhaps you should try to start a new plant from one of its branches? 

Bud drop is a common problem with Christmas cacti. Sudden changes in temperature, lighting, and watering can cause it to occur, so even the act of bringing it home from the store and into a new environment could have set it off. Now that the plant has adjusted to its new home, it shouldn’t drop its buds, as long as its care is kept consistent.

It sound like too little water and/or too much direct sunshine. Is it planted in cactus soil (a special mix); you could try that as it better controls the moisture than traditional potting soil. And remember, though it is a cactus, it comes from the humid forests of Brazil, where it lives epiphytically on tree branches, meaning that it doesn’t sit in water, but doesn’t get bone-dry either.

Water it a little and gradually a little more. Do not soak it. And allow it to dry out between waterings. Too much moisture in the soil will cause the plant to rot (leaves will drop). Water sparingly but consistently in fall and winter, and keep it out of direct sunlight, just give it bright, indirect sunlight.

In theory this could work; the only thing that might be an issue is water. Christmas cacti like warm, humid, shady environments, but will not tolerate being over- or underwatered. So if you do plant them outside, make sure you place them in an area where the soil doesn’t completely dry out nor stay wet for too long. Good luck!

If the sections have roots already, they can be replanted. If not, their stem ends should be placed in slightly moistened soil, sunk about an inch or so into the soil. After about six weeks, they should have roots and can be transplanted to larger pots.