In general, home gardeners do pretty well with Christmas cactus, both the real thing (Schlumbergera x buckleyi) and its close relative, Thanksgiving cactus (S. truncata), which I’ll call “seasonal cacti” in this article. (Read When your Christmas Cactus Blooms Too Early to know how to distinguish between the two.) In many homes, they come to bloom twice a year, in November/December and again in February/March. And they live for decades with only minimal care. But sometimes you start to notice that all isn’t right. The “leaves” (stem segments) go from shiny, green and plump to dull, thin, shriveled, soft and sometimes even reddish. What’s going on?
Not a Leaf in Sight
Banish the word “leaf” from your vocabulary when thinking about seasonal cactus. They have no leaves at all or rather, no longer do. Way back when they sprouted as seedlings, and that can be 40 or more years ago, they did bear exactly two cotyledons (seed leaves), but ever since, they’ve been getting along strictly using their stems. The flattened green stem segments link together like a chain, eventually forming an arching, hanging plant and even later, turning brown and woody (at least the very oldest stems do). Being green, stem segments carry out photosynthesis like a leaf would and keep the plant fueled in energy. But still, stem segments just aren’t leaves.
When stems become soft and shriveled, it’s essentially because they are thirsty: not enough moisture is reaching them. Logic would seem to suggest they simply need to be watered more, but that’s not necessarily the right thing to do.
Lack of Water or Too Much?
There are two main reasons why moisture fails to reach the stems, especially the last segments. Either the soil is too dry or the roots are damaged … and the latter can actually be caused by too much water!
If the Soil Is Too Dry
If the soil is too dry, that’s easy enough to see or, at least, to feel. Touch it. Your fingers will easily feel the dryness. So, if dry soil is causing the shriveled stems, yes, watering is the obvious solution. Not just a light watering, but a deep, thorough watering, so that the whole root ball is thoroughly moistened.
Sometimes, when potting soil is very, very dry, it repels water, so when you water the plant, moisture no longer penetrates the soil, but runs off immediately into the saucer below. This is especially common in hanging baskets, which we tend to water more lightly than we should, fearing any surplus water will pour out of the saucer onto the floor. As a result, the poor plant never gets enough moisture and is constantly drought-stressed.
If that’s your diagnosis, don’t just water the plant, soak the root ball. Plunge the pot into a sink or pail water of tepid water and let it soak for 10 to 15 minutes. Then let it drain thoroughly. Once rehydrated, the soil will become water-receptive again and you can water normally in the future … unless you allow it to dry out too once again.
How Often Should I Water a Seasonal Cactus?
Seasonal cacti are not desert plants and don’t need to be kept dry like desert cacti. Although quite forgiving of irregular care, they do prefer “even moisture” throughout the year. Just follow the golden rule of watering: water deeply, enough to moisten the entire root ball, then allow the soil to dry before watering again. It works every time!
When Soil Remains Wet
If your plant shows shriveled stems, but the soil is still moist to the touch, it’s obvious the problem is not related to underwatering. The situation is, in fact, much more serious. This occurs when the roots are dead or dying!
There are many reasons why the roots can be in such bad shape. Here are the two main ones.
- Soil kept too moist. If the potting mix is constantly wet, oxygen can’t reach the roots which, unable to breathe, start to die. Then root rot sets in. This is a disease caused by various pathogens—Pythium, Phytophthora, Rhizoctonia, Fusarium, etc.—whose spores lie dormant in most soils, ready to spring into action whenever root cells start to suffer. The disease then spreads from the dying roots to living ones, killing them in turn. Obviously, without roots or with fewer roots, the plant can no longer correctly hydrate itself, even if the soil is soaking in moisture, and its stems begin to shrivel. It reminds me of The Rime of the Ancient Mariner: “water, water everywhere, nor any drop to drink!”
- Mineral salt buildup. Over time, usually over several to many years, salts accumulate in any houseplant’s potting soil. They’re present in small quantities in the water you apply and in even greater quantities in fertilizer. When they increase too much, there comes a point where the soil contains more salts than do the roots. Water will then flow from the plant into the surrounding soil to dilute the concentration (this is called osmosis) rather than from the soil into the plant. As a result, the roots lack water and start to die. Often, the accumulation of salts in the soil is accompanied by a whitish or yellowish crust on the rim of the pot or even on the stem of the plant. Epiphytic plants such as seasonal cactus are especially susceptible to mineral salt damage.
Change the Soil to Save Your Plants
If you suspect that mineral salt buildup is causing the problem, the easiest solution is to repot.
Unpot the plant and remove as much of the old soil as you can. If the roots are rotten (they’ll smell like rotten potatoes), prune them off. Prune out any rotting stems as well. Now repot into a clean pot (with drainage holes, of course). Note it need not be a larger pot. In fact, if the plant has lost roots, it’s often best to repot it into a somewhat smaller one. Any potting mix that drains well (houseplant soil, cactus soil, orchid mix, etc.) will be suitable.
Water well to moisten the soil initially, then modestly for the coming months, only when the soil is dry to the touch. Usually, the plant will readily produce new roots when given fresh potting soil and its health will begin to improve. Still, you have to be patient: it may take several months before you see a clear improvement.
Take a Few Cuttings
Also, whenever a seasonal cactus is looking a bit off, it’s always wise to take cuttings in case you fail to revive the original plant.
For best results, choose stems with at least three segments (four or five would be even better). To remove them, twist the stems rather than cut them: they will separate quite naturally at the base of a segment.
Insert the cuttings into a small pot of slightly moist potting soil, completely covering the lower segment in mix. Keep the mix slightly moist until new growth appears and that can take several months.
One of the reasons I suggest combining taking cuttings together with any other rescue method for a declining seasonal cactus is that sometimes very old specimens don’t respond well to repotting, even when you’re doing it to save their life. They seem stuck on their old ways and prefer to die slowly rather than accept a change for the better … like some older humans, by the way. The cuttings thus become your “backups.”
Good luck saving your Christmas and Thanksgiving cacti!