are you using 1/2tsp every time? If you're fertilizing every watering, you should only be using 1/4tsp. It could be that the cactus wants to go dormant. Too much water + not enough light would be the more likely cause of rot.

What a bummer that's one of my fav cactus Stetsonia coryne aka Toothpick cactus;). They have some of the most vicious spines around;). They're not flimsy either. Very woody.

I second what SucculentCity had said:). Too much moisture for the cold dark winter. The fertilizer is not necessary during the winter for this cactus. So that likely didn't help either. For most cactus they really don't need all that much fertilizer even during the growing months.

I wonder if you could save that middle. I'm guessing the bottom part is rotted.

Debbie, I have had (over several years) much of the same experience you have had with gritty mix. I have made my own and, in the beginning, it included Turface, chicken grit and small bark. It was too water retentive. I eliminated the bark. For awhile I just used Turface and grit. That wasn't much better.

I decided that for me, Turface was not a winner. It was mildly okay in clay pots, but in a plastic or glazed pot it stayed wet for much longer. I think it also compacted the mix too much. Today I use a mix of Manna Pro poultry grit, sifted and washed pumice (I buy from General Pumice Products -- not cheap to have sent, but a good product for me), and maybe a tablespoon of Turface, or else an equal part of perlite. I also have many of my Haws in pumice alone. I like mixes that are "gritty" overall, but for me -- it has taken years to determine what works for my conditions, plus a lot of experimentation.

Aren't you doing the skewer trick before watering?

As Kara suggested, this could be really interesting as a cutting. If you try it, let us know how it goes.

Is that glazed pot? They don't dry up as fast. It is also quite large, and more mix may take longer to dry up. Premade mix could be great, or could contain some fine particles, especially if handled a lot (storing, shipping...) I never bought any pre-made mix, but quite a few ppl mentioned that they had o screen BJ mix.

I just looked up their Succulent soil ingredients list (you said that's what you are using). The size is listed as min. 1/8th, max. 3/8ths. That is wide range - and 3/8 seems too large to me. That is what I use for top-dressing. BUT I never had any of their mix, so maybe shouldn't comment...

I think I would cut below the rot - make sure it is sound flesh - and just leave the bottom part in the pot - it is already rooted. It will grow a new growing point - which you can leave where it is - or cut off and root. Like this Myrtillocactus geometrizans. Sorry the pic is so carp.

Debbie

I am sure it is better than 'dirt' soil. Bu, IMO (that probably doesn't matter anyway, lol), difference in particles sizes is just too big - and I am judging only from description they gave. Maybe I am just not seeing it, but they didn't specify which media is what size. If the inorganics are similar size and only bark bigger, it is probably OK.

I don't use bark anymore because to find it in smaller size is almost impossible. Here is a thread where I posted photos of gritty mix I make; there are 2 sizes: few gritty mixes . There are photos of what Crenda uses and Kara posted hers too.

I use very few clay pots because they are heavier and crack easily. But maybe I am just clumsy :). Plastic is it for me, easy to get (most of them are free; I recycle a lot); easy to clean; light; they have usually many drainage holes; uniform size is easier to fit and handle; many sizes are easy to find - more than clay pots; if I have to buy any - they are much less$...which I rather spend on plants. But I agree, most will not win any prize for their looks.

Some cuttings in 4" plastic just potted up - easy to carry wherever they need to go - these are free/recycled including a tray:

Unless the rot has already traveled all the way up before manifesting near the top of that cactus, I would think you likely had some other issue also at work.

With your being z5, there is another point to consider in addition to what others have mentioned ... the temperature of the growing area. If like most folks you keep your home cooler during the winter, then not only will your media not dry out as fast, but you are raising the odds of rot to begin with. For cacti and many succulents, cool moist conditions is a recipe for rot. My cacti/succs are on windowsills or the floor next to sliding glass doors. During the winter, except for the winter growers, they get watered lightly once every 2-4 weeks.

Debbie

I have a question about your beautiful jade. You said it is in 10" pot. How tall is it? Is it glazed? How big is the plant? What is the circumference of the trunk at the soil line?

Debbie

I wouldn't recommend to keep plants so thirsty that thy are shrivelling all the time before watering :) It is good indicator that they are thirsty, but relaying only on that in order to water them seems to be bit of torture to me...In general, succulents will recover easier from being underwatered than overwatered. And I wouldn't worry about going away for a week or two and leaving them without water. But, everything in moderation, right?

Temps you keep your plants in are warm, and they should be watered. They should not be in cold temps and wet soil - that's exactly what Paul suggested. I also have few in space that gets close to 40*F at night and 50-52*F during day, and they are getting water maybe 1x/mo or even less.

I was wondering about size of your jade comparing to size of the pot. I have few that are similar size, and they are in 5" & 6"pots...that is getting too small and they need to be repotted soon. I do not like very deep pots, and will go just little bigger. Here are couple (sorry for bad photos) that are 17" and 19" respectively; first one in 4.5"pot and taller one in 6.5" pot - repot and pruning is coming:

For arid cactus I use unglazed Terra Cotta pots and the mix is pumice and no more than 10% Turface. Normal gritty is far too moisture retentive for those. I don't water more than once a week in the summertime and not at all in the winter. The plants are in full sun outside.

I can keep jades in regular well draining potting medium. They are super tolerant of water.