We have had a grafted cactus for about three years now, growing indoors on a sunny, south-facing windowsill (in the northern hemisphere). I’ve attached photos. It may be something like a Gymnocalycium grafted onto a Hylocereus. It’s a super, robust little thing and it’s now about six inches high. the green base is shaped like a Y in cross-section, but not even-angled, so closer to a T.

Over the last couple of months, it’s developed two problems.

First, (please see detail photo attached), a it has developed what looks like a dry, dead patch just above the soil line, on one of the three ‘vanes’. Any idea what’s doing this? Overwatering?

I unpotted it to check the root mass. As you can see from the third photo, the roots are very shallow, extending barely an inch and a half below the surface. I don’t know cactus, but they also look sparse to me. Again, might this be a result of overwatering? I water by immersing the pot. The medium in the bottom of the pot is therefore likely to be wetter, longer.

Second problem, with its sparse roots but robust growth above ground, the cactus has become top-heavy and begun to lean. We keep straightening it, but it keeps leaning.

Help! Can we confirm this is overwatering? If so
1. What should be the watering interval?
2. Should i be watering from the top, not the bottom?
3. Is the current 3-inch diameter pot still about right?
4. I can’t re-pot it deeper to help stability, right?
5. Is there anything I can do, aside from lengthening the watering interval, to promote root growth and save the cactus?
6. Can I stake the cactus while it recovers, to keep it upright and eliminate mechanical stress on the roots that remain?

Big question, is the bottom dark spot soft. If it is hard like wood, replant and water it. The top portion is a desert cactus and needs little watering however the bottom section is a tropical cactus and needs watered more often. I think they use this because most people over water their plants.
If the bottom is soft and is rot, then the only thing you can do is cut if off to good part, let set for a few days and replant in solid perlite and just mist it once in a while until it gets new roots. The very top section can not live on it's own and must stay attached to the green base.
Hope this helps.
I am no expert so I hope you get more replies.
Stush

It does look like a case of overwatering. Hylocereus is a tropical cacti but it still needs proper interval in watering. With my cacti and succulents, I always water from the top and let the water drain out. Succulents hate very wet and soggy roots. OOps, editing to add..you were asking about what is proper interval in watering..it will vary depending on your growing area there. You just have to see if your media is still looking moist, then don't water. Allow to dry a bit but not too dry since Hylocereus is not a desert cacti. You can use toothpick or bamboo skewer, if you stick it in and comes out still wet, then no watering needed. Or put a big stone on the container beside your cacti, if you lift it and it shows moist below, then media is still wet.

Root mass of cacti is typically shallow, I would not recommend making your container too deep, since it will make more media stay wet longer. Your Hylocereus cacti is just growing as its growth habit wants it, getting longer, so it is not that the yellow cacti is getting too top heavy, it is the Hylocereus doing its natural growth habit, elongating. Usually it is just allowed to ramble about or some would even tie it to a post and it has roots that can attach to the posts or stems later on.

I do not know if you are willing to attempt to do a re-graft of the yellow one, choose a different cacti rootstock, something more upright growing and can carry the yellow better, both with similar watering needs too. But you may have to wait till it is warmer weather to do it.
Here are two videos about it and see if you are willing to try, good luck!
https://youtu.be/rikUpPDvu4g
https://youtu.be/eLCrMi88llo

Bad news: your bright yellow Gymno is a parasite on the green Hylocereus (the usual graft recipient). The Gymno is sucking the Hylo dry. The Hylo is trying its best to keep both alive. Its a hopeless case. The only outcome is death for the Hylo. You either have to re-graft the Gymno to a new recipent or call it a loss and start again with another blood sucking parasitic plant.

Daisy

Shush,

Thanks so much. The bottom spot is more light than dark. It's more hard like wood than spongey like rot, but more like paper I would say, The 'vane' of the cactus is thin at the bottom and whatever this condition is, it runs right through the vane from one side to the other. I'm attaching another photo in close-up in cast that helps determine what it is. What do you think?

I was very interested to read your comment that the bottom cactus can use watering more often as a tropical. Crossing my fingers, hoping that means we've not overdone it.

Tarev,

Thanks so much for your comprehensive reply.

• I will water from the top now -- I see how that makes sense.
• I'm encouraged by what you say about watering: I've certainly let the medium dry out before re-watering. if anything, it sounds as if i might have been a bit too sparing with the water, for this tropical cactus.
• Your info suggests re-potting in a shallower, wider tray or dish rather than a traditional pot. Maybe the roots would then spread laterally to provide the support that's missing just now; and I'll stake for the moment while the roots are lengthening.

I might also try to adjust the medium. At the moment, it's contains a lot of perlite. If my cactus is tropical, I might reduce that proportion in favor of dirt and sand, The problem with the perlite-rich medium is that it's crumbly, so the roots can't bind easily to provide the anchoring and support necessary to keep the plant upright.

No plans at the moment to re-graft -- the graft is the bright spot, and is holding fast!

Thanks so much,

Daisy,

Yikes! The Hylo has survived the 'leech' effectively for three years. Maybe it's nearing the end of its resistance; or maybe it just needs more water (see previous replies) -- so I'm tempted to roll the dice on a smarter re-potting to encourage root growth, and more frequent watering.

I think I'll also re-jig the medium into a two-level arrangement: maybe an inch and a half of pure, fresh cactus medium over a bed of an inch or so of sand and pebbles (those tiny ones like gravel that you can buy in pet stores for fish tanks). That way, I'll be able to water more frequently (so the gymno on top can drink all it likes without sucking the hylo dry), but the medium will drain quickly, so the roots won't be kept in damp medium.

It's an experiment, and we'll see; but I'm reluctant to give up on the plant just yet.

Thanks,

I don't grow hylocereus, but I do grow epiphyllums, and it is also a tropical cacti. I combine orchid bark or those coco chips with some cacti soil and pumice. Try if this would work better for you. They are epiphytic cacti, so I kind of treat them like I am growing terrestrial orchids.

Tarev,

That's very interesting. I like the idea of the orchid bark or chips because withal, I'm looking at this plant's root mass, and it's apparent that it's asking too much of it to expect it to hold the relatively massive plant upright. BUT, if those roots could bind to something, orchid-style, it might be a different story -- and intuitively, they are more likely to bind to something organic than to the pebbles i had in mind.

Just a thought - I might also be able to re-purpose some of that fibrous orchid medium and add it to the mix. What that stuff brings to the party -- maybe -- is a way to get the whole medium to bind together, something that's sorely lacking in the crumbly mess I have now.

Thanks again.

tarev said: I don't grow hylocereus, but I do grow epiphyllums, and it is also a tropical cacti. I combine orchid bark or those coco chips with some cacti soil and pumice. Try if this would work better for you. They are epiphytic cacti, so I kind of treat them like I am growing terrestrial orchids.

Although the Hylo is a epiphyte, its also still a cactus. Treat it like a cactus that needs a little more water.

The Gymno is a naturally occuring mutant that does not photosynthesize on its own. The Hylo is supporting both plants. When the Hylo fails, which yours is, the Gymno will die also, unless regrafted. All plants grow from the tips. The Hylo's growing tip has been replaced by the Gymno. The Gymno continues to grow but the Hylo can't. So the same amount of Hylo is supporting a bigger and bigger Gymno.

Three years is pretty good for this plant.

Daisy

Okay, I understand now. O sage.

Hmm. A doomed frankenstein's monster. There are many lobes on the Gymno. Perhaps i prune most of them off, cut the Hylo in half, say, and hope the top half with the reduced Gymno will strike roots and be viable (for a while). Meanwhile re-plant the bottom half of the Hylo by itself and see if it recovers.... I'm sure I lack the skill to re-graft anything.

Thanks, and sorry for not getting what you were trying to explain, the first time....

DaisyI said:Although the Hylo is a epiphyte, its also still a cactus. Treat it like a cactus that needs a little more water.

The Gymno is a naturally occuring mutant that does not photosynthesize on its own. The Hylo is supporting both plants. When the Hylo fails, which yours is, the Gymno will die also, unless regrafted. All plants grow from the tips. The Hylo's growing tip has been replaced by the Gymno. The Gymno continues to grow but the Hylo can't. So the same amount of Hylo is supporting a bigger and bigger Gymno.

Three years is pretty good for this plant.

Daisy

Frankenstein's monster! I like it. I always refer to them as the blood-sucking plant abominations.

If you could save the Hylo, they are actually pretty plants. I have seen a few that the "heads" have fallen off and the Hylo grows arms and survives the adventure. The usual Gymno graft recipient is Hylocereus undatus (Dragon fruit).

I don't know if reducing the size of the Gymno will save the Hylo.

Daisy

Wandering a bit off-topic, It is a while since I've read Frankenstein, but if I remember right, the poignancy derives from the fact that while the monster has enormous power and vigor, it is at the cost of a limited life-span -- not dissimilar to that of the Gymno-Hylo graft. While we're all doomed to die from birth, the monster has an unnaturally brief life-span. The same plot device (wandering further off-topic) recurs in the movie Blade Runner and the Philip Dick novel that spawned it, Do Androids Dream Of Electric Sheep?

I will try to save the Hylo by, er, disengaging the Gymno entirely. And saying bye bye. It would be super to see the Hylo grow arms. When I re-plant it, can I plant it deeper in the medium, so the dried/light-colored/papery part is below the surface?

Sorry to ask for a further botany lesson, but if the Gymno is a pure parasite, i.e. cannot subsist without a host, how does it find a host in nature? Other posters have emphasized that the grafting process is not straightforward -- so if it's problematic even with human beings helping, what's the process in nature?

It does not exist in nature, they are mutants manipulated by some enterprising/adventurous growers.

No, do not bury the dried out part below surface. Cacti may just try to heal and callus, and harden it/cork it. As long as it is staying firm, and not mushy, it may just heal naturally.

This is not the best example, but epis grow like hylocereus, so I just let the plant heal itself. I also get those brown marks below, but it will dry out and plant survives. Really important to provide good air circulation, light and warmth.
This is an epi, not hylocereus..just to give you an idea:

Nice comparisons, Quourteous. Frankenstein it is.
Moon cactus are Gymnocalycium mihanovichii that have a naturally occuring genetic defect (in this case, a lack of Chlorophyll). The first one was found in Japan in the early 1940's and grafted to another cactus to keep it alive. Some enterprising person took advantage of that defect and started hybridizing for the defect. The plants are produced by harvesting the offsets off the "mother" stock (which is also grafted to a Hylo). The Hylo grafting recipient is produced from rooted cuttings.

Tarev is right; don't bury the Hylo any deeper than it is. If it continues to fail, even after having its big yellow parasite removed, you may have to cut the Hylo from its roots and reroot the stem you have. They root very easily.

Daisy

In the recovery room... Patient bearing up bravely...

Looking good!

Still looking good? should I have done something to cauterize the area from which the Gymno was removed?

Is it getting mushy? That gray area doesn't look good. Maybe someone will have a thought.

Daisy