My Echeveria sits on the windowsill in my living room and for the past two weeks it's been getting brown, soft spots on the leaves. I only water it every 2-3 weeks, but now I'm wondering if I'm doing something wrong or if it's a fungal infection. The soil also smells a bit musty.
The musty-smelling soil is your main problem - it points to waterlogging and root rot, not primarily a fungus. Echeverias are succulents and really need very little water, but what's even more important is that the soil has to dry out completely between waterings. If the soil smells musty, the roots are probably already rotting, and that's what's causing those soft, brown spots you're seeing.
Take the plant out of the pot and check the roots. If they're dark, mushy, or smell musty, you need to cut away the rotted parts with a clean knife and repot the echeveria in fresh, well-draining soil (ideally special succulent soil or regular soil mixed with a lot of sand). Use a pot with drainage holes and don't water for the next two to three weeks - let the cut areas harden off first.
Your location could also be playing a role. Echeverias love bright light and need good air circulation; if your windowsill isn't particularly airy or is too dark, that makes the rot problem worse. After repotting, you should plan for longer dry periods and only water again when the soil is really dry - two to three weeks is a good rhythm, but in winter it can be even longer.
At my place at home, I had the same problem - brown, soft spots on an Echeveria, and in the end it turned out to be both at once. The musty soil is warning sign number one. It smells that way because the roots start to rot from too much moisture staying in the soil. That also creates the perfect climate for fungi and rot bacteria, which then attack the leaves.
The most important thing now: change the pot and soil. Take the Echeveria out carefully and look at the roots - if they're brown and mushy instead of white and firm, then your suspicion is confirmed. Remove all the old soil and cut away the rotten root parts with a clean knife. Fresh succulent soil (or regular potting soil mixed with lots of sand/perlite to make it looser), and the pot absolutely needs to have a drainage hole.
When watering, really go easy on it - for me the rule of thumb is: only water once the soil is completely dry. Maybe every 3 weeks in summer, even less in winter. You should remove the affected leaves - they won't look nice again.
The problem is probably a combination of waterlogging and poor air circulation - that musty soil is the red flag. Echeverias need not only minimal water, but also loose, well-draining substrate (ideally mixed with sand or perlite) and above all a pot with drainage holes. What people often miss: even if you water rarely, the soil can still stay wet for too long if it's compacted or the pot is too large - then it basically ferments. Repot quickly, remove the soft leaves, and change out the soil completely, otherwise a fungus will take hold and make things worse.
# Translation (German to English)
for nothing if the soil smells musty the echeveria needs to be repotted quickly - that's definitely root rot and not just a surface fungus. the brown soft spots are often already the late stage because the rotting roots aren't supplying the plant anymore. cut off all mushy leaves, take the echeveria out of the pot and look at the roots. if they're dark brown or black and smell mushy, throw them away. the healthy roots are light colored and firm.
fresh soil is now essential - regular potting soil is way too nutrient-rich and holds too much moisture for succulents. get yourself special cactus or succulent soil, it's much looser and drains better. if you can't find any, mix regular soil with sand or expanded clay in a 1:1 ratio, that works too. the pot absolutely must have a drainage hole, otherwise you're just repeating the same problem.
when watering: even every 2-3 weeks can be too much, it depends on the season and air humidity. in summer you only water again when the soil is completely dry (really completely) and in winter it needs almost no water. the windowsill is actually good, but the echeveria needs a lot of light otherwise it gets weak and susceptible to problems. if the leaves look thin, too little light could also be part of the problem.
Quickly take the plant out and check the roots - if they're black and mushy, it's root rot, not just a fungus on the surface. The brown soft spots are often already the last stage before the whole plant collapses. Repot it immediately into dry, coarse cactus or succulent soil (regular potting soil holds too much water), and then let it dry out completely for a while before you water again. Keeping the musty soil and just reducing watering won't help anymore - the problem runs deeper in the roots.
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