Stop using fertilizer sticks. In fact, stop feeding altogether until, 1. the Marginata resumes health and 2. it sends out new growth.
When you resume fertilizing, use a powder or liquid form.
Those sticks are useless..they basically fertilize the area their placed in..in other words, the entire rootball isn't getting fertilized.
Also, you're giving your plant more fertilizer than water. That's a no-no.

What do you mean, puffy stalks and puffy roots?
Also, why do you water using 3/4 cups? Depending on pot size, 3/4 cups isn't enough water. When plants get a drink, it's best watering in a circular motion so soil is evenly watered. If your pot is larger than 4", and I'd bet it is, your plant isn't getting adequate moisture.
Don't bother measuring or choosing certain days to water. When soil is a dry, give it a drink. D. Marginatas dislike wet feet. They rot..It's a good thing you noticed the mold, and even better it hasn't returned.

What did your son do? Gave it a big shake? Do you mean he literally shook the trunk? lol. That surely won't help..
I wouldn't discard the trunk. Marginata leaves wilt when soil is too dry or too wet.
It's possible it has salt build-up from too many fertilzer sticks.

I would first shower/hose soil (leach) until water drains out of drainage holes. Set your plant where it will get at the minimum, medium light. Since it's winter, a south or west window will be fine.
Do not rewater until soil looks and feels crumbly. Stick your finger into soil. If your finger comes out wet, wait a few days, and retest. A probe would be better than your finger, especially if the pot is deep..
When soil feels/looks crumbly, or if you lift pot and it's lighter in weight, 'than usual,' it's time for a drink.

Any sticks you see, remove.
One last thing...check leaves for insects..I don't think this is the reason leaves are wilting, but it's always good to be on the safe side. Look for webbing, dark or light lumps, or white, cottony splotches.

Good luck. Please give it a try, don't toss your plant unless you're positive it's dead. If the trunk is firm, it's alive. Toni

The disease I mentioned, and other soft rot diseases are usually first noticed on the basal (bottom) portion of the plant, most often at or just above the soil line or in roots. The affected part of the lower stem gets wet looking and dark, before it turns dark brown dark brown and turns spongy. The periderm (bark) usually separates from the cambium, which is the 'puffy' symptom you described. It also usually has the same odor as wetwood or slime flux in trees - a sour smell.

If all the stems have a common root system, it's unlikely the plant will maintain viability over the long term. If they are separate plants, started as individual cuttings, I would remove the infected plant and the associated roots, and repot the remaining cuttings in an appropriate soil - one that is durable, well-aerated, and free-draining. In advance, I'll say it's a poor time to be repotting, but desperate times call for desperate measures. Your call.

Fertilizer sticks provide nutrients in a form that is slowly soluble. As soon as the nutrients dissolve in the soil solution, they disperse throughout the container, so it's not true that they only fertilize in the immediate area of the sticks. Think of a sugar cube or teaspoon of salt dropped in a cup of cold water. As soon as the sugar or salt goes into solution, it evenly disperses throughout the water and reaches an equilibrium (isotonicity). The same thing happens with the sticks and the soil solution (water in the soil).

For a number of reasons, though, I don't like fertilizer sticks and would avoid using them if I could, though they are better than nothing if used appropriately.

Did I understand correctly - that you potted up, then returned the plant to the smaller pot it was originally in? Commonly, I suggest that you leach the container to try to ensure the level of soluble salts is as low as it can be, while still maintaining an adequate charge of nutrients in the soil, but how you decide to proceed with regard to what you do about the dying plant and repotting would probably have an impact on what steps are most appropriate .....

Al

Al

Thanks
BT