I agree with Socks. When repotting look at the roots, is soiil moist of wet there? Are the roots in good health? Especially under the pups doing poorly, do they even have roots? After repotting, leave the plant unwatered for a week or slightly more. By terracotta, Socks refers to what I call red clay pots. Clay is better for cactus as it helps keep the soil drier.

thanks for the responses! may I ask what the benefit is for using a shorter pot? I just assumed more room for roots to grow, the better.

Mine did the same thing so I gave it away and will one day try again with another. I think what happened with mine was it didn’t like being treated like an arid type cacti. Some say this cactus is a form of Acanthocereus tetragonus and Acanthocereus are found in tropical regions of the Americas. Then other people say it’s a form of Cereus hildmannianus or Cereus hildmannianus subsp. uruguayanus, and like Acanthocereus come from tropical regions. So basically I think these guys don’t like to being super dry. This doesn’t mean put them in moisture retaining soil, but probably would like being watered a little more frequently then a cactus from the Mojave desert;).

If this were mine I would unpot to check the roots just to be safe. Not the best time to unpot because winter is right around the corner, but your cactus is in a warm house so it shouldn’t matter. If you notice the roots aren’t that abundant go down a pot size. Pot should have a drainage hole. Repot in a fast draining mix like Socks has mentioned you can up the perlite or pumice so it can dry out faster. You don’t want it to stay wet even tho I’m under the impression they like a little more water. Fast draining mixes allow you flush the roots more frequently with water if need be because it dries out quicker. Keep in mind mixes stay damp longer when inside. Good airflow is very important too.

Another reason why I think cactus turn yellow is because of strong light. I doubt that’s what’s going on with yours, but keep that in mind.

I’m not totally sure what’s going on with your cactus because tbh I never get a solid reason why cactus turn yellow. It’s always a handful of reasons, but I think it was the low water that made my FC cactus look sickly.

Most cactus roots aren’t impressive and don’t grow deep, but more close to the surface. They do better with less room. More room equals more soil/mix to retain moisture.

Let's say your cactus has roots only as big as the top part, so the roots will extend maybe only halfway down into the pot. The mix below that point will stay wet too long because there are no roots to take up water, and your whole pot will be too wet.

It's a very pretty pot but would be better for a houseplant like a schlefflera, assuming it has a hole.

So I just went to re-pot the cactus and I saw no signs of root rot and it looks like the pot is not too large for the plant as the roots go almost as deep as the height of the pot. Do we think there's a chance it could be the opposite problem in that the pot is too small and that I should size up? Attaching pics for reference. In the meantime, I re-potted it back in the same pot with fresh cactus-specific soil and will wait a few weeks before attempting anything more.

No that pot is definitely not too small for the roots. It’s fine in that pot, but I hope it has a hole at the bottom;).

yes as i mentioned in my original comment the pot has drainage...i wouldn’t be that cruel of a plant parent lol

Oh sorry I must have skipped where you said that;). Drainage holes makes life much easier!

Keep us updated with what happens because like I said mine did the same exact thing. I’m curious if it will go back to green.

Ok, then carry on and good luck. Maybe the change of mix will help.

Did you add perlite or pumice to the soil as socks suggested?

My experience is that these plants grow very tall and require a deep pot to allow the development of a deep root system to hold it up. Putting shipping peanuts at the bottom of the pot along with a good potting mixture should help with drainage. They are very beautiful and keep their shape adding offsets as they grow. It's in a great spot so it should do well for you.

Overpotting is an easy way to kill a cactus. This cactus is far off from being top heavy.

Somewhat agree, Kara. Firstly, a deep pot and a big pot are not synonymous. Secondly overpotting never killed cactus. Overwatering maybe, but not overpotting. I grow mainly outside in pots and use large pots with very free draining soil for all my cactus as it is not fun to repot. My experience with this cactus is that it grows quickly and tall so a deep pot, not necessarily large pot might be appropriate.

One can grow small succulent in huge pot, as long as potting mix drains well - just as jstropic said above.

Problem is that ppl are often too 'generous' - or think they need to give plant lots of soil in order to grow well. Lots of water-retaining soil means that it stays too wet for too long, and that often means rot is a big possibility.

I am guilty of using pots that may be on smaller side for size of plant - but that is mainly because of lack of space...I know many of my plants could be potted in bigger pots, and I would if they could stay outdoors year-round. Iam using very well draining, mostly inorganic mix.

root rot doesn’t appear to be the issue as you can see in the photos i posted in a comment earlier. i always use a cactus specific soil (and drainage hole) and then use a moisture meter to ensure i allow it to dry out appropriately before watering again.

Jilian

From what others said (I do not use bagged cactus soil), it is often not as free draining as it should be. That is why many users add lots of perlite or pumice, in about 1:1 ratio. Mix looks like this:

I stopped using moisture meter many years ago because it wasn't working that well. Mind you, it was a cheepo and you may have much better one.

For a while, I used a wooden/bamboo skewer to check for moisture (chopstick or pencil work too). Insert deep into mix and leave for few minutes. After being pulled out, it should be dry and clean if mix is sufficienly dry, and plant should be watered. Otherwise, one should wait longer. After some time of doing it, I can pretty well tell when plant needs watering, but if I have any doubts, I still use a skewer.

I have some quite deep pots, mostly for haworthias that tend to have deeper roots. They work well, and I use very well draining mix (mostly inorganic) - often no soil at all, and sometimes just a little (maybe 10-15% of total).

From what is visible in your photos, roots of your plant seem to be thick and growing quite deep. If my plant, I would clean off all existing soil from the roots to see if they are same thruout. If there is lots of peat in the mix, some my have become hydrophobic around the rootball. If that happened, it doesn't let water thru to the roots. Just one possibility - I am just looking for what else could be reason for plant yellowing.

Did you make sure it was not only the sides of the cactus facing the window that discolored?

Hi @Gabby C (FL 9A), I try to regularly rotate all of my plants so that they get more even lighting, so the discolored area is not the only area to get direct sunlight.

@rina_Ontario,Canada 5a I did scrape off a lot more soil than what I showed in those pics (took them early on before my hands got too dirty) and throughout the de-potting process I did not notice any major clumping that would cause concern re: your hydrophobic comment.

I plan to re-pot into a larger pot in the spring since the roots have run out of room in this pot and per other people's comments these types of cacti tend to grow deep roots, and I will make sure to add additional perlite to allow for additional drainage.

I would consider the amount/strength of sunlight the cactus gets and also the water you use for the cactus, if it is tap and what could be in it. Some plants are sensitive to tap water others are not. Both of those factors can cause plants to loose color.

Jillian, sorry this is late, but I’ve been super busy:). I think once you add perlite or pumice your cactus will be much happier. I personally think when growing most new small succulents it’s best to use an appropriate sized pot, let the roots fill out that pot, and then repot every other year. From what I can see your cactus’ roots have hardly filled out that pot.

The biggest issue at hand is the mix it’s been grown in, and once you find a mix that works it should really start growing for you. The roots on your cactus are the type of roots I’ve seen many times when I unpot succulents that have been grown in high peat mixes. Most succulents need to dry out, but when peat dries out it becomes like a rock and really chokes the roots. Then when you try to water the dry hard peat it repels the water. Once you amend with 50%-60% perlite or pumice the peat won’t do that anymore.

I wanted to say your big Cereus in the back is beautiful. He seems happy. This may sound stupid, but I’ve had a couple pots that no matter what succulent I’ve planted in them the plants have never thrived.

Jstropic, a deep pot and bigger pot may not be synonyms too you, but too me they are. I know you didn’t ask, but I’m gonna be a be a brat right now and share some synonyms for deep which are cavernous, gaping, huge, great, extensive, and big. So if someone were to advise me to get a deep pot I would go get a huge pot for a cactus that has roots that aren't ready for it. I just don’t want somebody to get a pot that’s cavernous.

Rina hit the nail on the head when she said “people are often too generous“. Overpotting is probably the top three issues I see on this forum. Imo let the cactus above fill that pot first because anything deeper would be overpotting. Plus this cactus I believe is grown inside which slows evaporation down.

Tbh tho I think the biggest issue is the mix.

To go with what Gabby has said about the tap water. From what I’ve read Acanthocereus tetragonus likes its soil ph around 6-7.8 so between the water and soil the ph levels could be off. That could certainly turn a cactus yellow. Llifle also says this particular cactus may be sensitive to salinity.

Kara, thanks for explaining your misunderstanding, no need to apologize. I wanted explain that a pot that's depth is greater than its width can have an area that is less than a pot that has a width greater than its depth. In other words the shape of a pot doesn't determine it's size. Sorry about the confusion.

I think @Kara 9b SF Bay Area CA may have hit the nail on the head with the salinity. Your high peat mixture is also going to hold more salt. A mixture higher in drainage will not just allow water to drain, but when you water your cactus in the future, the extra salts from fertiliser and possibly your tap water will be flushed out each time. This is how those people using extra grittier mixes are able to fertilise their plants more often, because the salts get flushed out of the mix each time they water.

Someone did recommend you adding something other than potting mix to the bottom of your pot, this is should never be the case. The potting blend should be the same blend from top to bottom, when you interrupt the flow of water with gravel or even a different type of potting mix you can create perched water table. The mix has too become completely flooded before it crosses into this new substance, creating the opposite of drainage.

I keep forgetting to provide an update, but repotting and/or watering more frequently (small amount every other week, not enough to have water drain all the way through) seems to have done the trick! it’s regained color and i only lost a couple of small pieces of cacti throughout the whole process.

I’m glad you’ve done an update because I was never sure what the real issue with my FC cactus was, but always felt in my bones I wasn’t providing enough water from the start. Yours looks really goo:) and the next FC cactus I buy I will definitely water more.