Why not take a mignifying glass and look for creepy crawlies?

Suppose the seeds of one species happen to be infected with a fungus, if you put them in the same bag as the seeds of another, not infected species: both will eventually become infected.

Rooting a cutting of Melocacti is difficult, grafting might be a better option if you really want to keep this specimen.

In his monograph on the cultivation of Melocacti George Thomson describes which rootstock is best.

Look at Silverhill Seeds (although it has been a while) or wait for it to appear on the seed list of the Mesemb Study Group (it is on the list every few years). They will have it on offer for a reasonable price. They are not easy, though! I have given up after a few tries (although the tries were n...

Next time microwave the soil and put the seeds in some iodine tincture for a short while.

May get more expensive than that.
I have been looking and am still looking for Muiria horteneae for a friend.
Found 10 seeds for GBP 130. It is said to be difficult to get them to germinate so suppose 2 germinate you have GBP 65 seedlings. In none germinates you have wasted 130 quid.

There's a lot of info, especially on Lophophoras as many people grow them for the drugs they produce. There are plenty fora dedicated to growing psychoactive cacti. This website has pretty much detail. It is in German but I found google translate does a good job here: https://lophophora-williamsii.d...

I am reading a lot about spider mites causing problems. I have only had them once in a Polyscias that they killed. Never in my cacti. I came across this stuff that is available in Germany: https://dr.staehler-schopf.de/produkt/kanemite-sc-spinnmilben-frei/ Getting good reviews on amazon.de Hope this...

You could cut off the top and treat both wounds with ashes. The top you can try to get to root, the remainder of the cactus will grow offsets at its cut edge that you can use for more cuttings.

This might be of interest.
https://gpnmag.com/article/developing-e ... t-program/