Right. So I've scraped the mould off the soil surface. Obviously I need to repot but in the meantime I want to keep it in check.

What would you try? Neem? Cinnamon? Hydrogen peroxide? Throw it away?

See whether it comes back and if it does I'd try diluted hydrogen peroxide. The plant itself looks very healthy so the effect of the mould is purely cosmetic. Soils are full of moulds, fungus, bacteria, etc. If they're not harming the plants they're usually aiding them.

The netting fabric indicates that the plant was grown in a peat plug. When it got large enough or was close to sale size, it was then plopped into a hole in the media of the current pot. Since the roots grow through the holes in the netting, nurseries make no effort to remove it. Understandable, but problematic should a person wish to clean all the old media off the roots for a repot. If you are used to growing plants in such peat heavy mixes, you might be fine waiting. Otherwise, I'd say do a repot now. The mold is still there, btw. The surface material you scraped away was almost assuredly the fruiting portion. The rest of the fungi system will be spread throughout the media. As far as killer my off the white masses on the surface, a spritz of rubbing alcohol will do the job.

Thank you both for the suggestions, I have peroxide and I have alcohol so I'll try one or the other to keep what's seen on the surface under control, mainly to reduce the family's exposure to it. Bit hypocritical of me as I encourage all those beneficial organisms and their interactions outside in the garden, but prefer to limit what we breathe in inside! Actually one of the lightbulb moments for me reading this forum was understanding that container plant mixes are not and cannot be the same as the soil in the garden. Great concept, explained well elsewhere, but I'm drifting off track...

I'm not used to growing in houseplants in heavy mediums - it's scary just how much water you can add and still nothing comes out the bottom! Then of course it stays damp for weeks. Some plants you buy here come in halfway decent mixes with lots of bark and pumice that drain through well and never get soggy. I doubt they have anywhere near the aeration of the gritty mix or 511 described here, but they're not terrible.

And then there are the other houseplants you buy that come in these peaty plugs. My other Calathea came like that, minus the netting. I immediately potted it up the instant I got it home, by plonking the entire plug, undisturbed, into a larger pot with a better draining mix around it. I know, I know. It gets worse : I based my watering on how the newer mix around the edge was drying out, which is what I could reach (and by checking the weight of the pot, to be fair to me). Needless to say the peat core stayed sopping wet, the plant started rotting, looked sickly, got spider mites etc.

At that stage I discovered this forum and have taken many steps I've learnt here to try to get it back on track. It's hanging in there now but not exactly thriving yet. Anyway, all of that is a long winded explanation as to my fixation on the mix (and what to do about it) in my new Calathea.

It's the start of winter here in NZ (BTW do I just put my zone in by editing my name on my profile?), so not ideal repotting time, but December is a long way away and I don't want this one to rot! Bite the bullet and repot now while/even though it's looking healthy? Or wait to see if it declines in which case repotting would be harder on it?

My son just told me this is SUCH a first-world problem. True!

With the temperatures you're keeping it in repotting now shouldn't really be a problem. They're a tropical plant used to growing all year so as long as it's kept warm and adequately moist it should be good. Which part of NZ are you? I'm in Au near Darwin. I've only ever been to the North Island.

We're middle North Island, Waikato, just around the corner from Hobbiton - you know, Bored of the Rings! We do get a bit of the extremes - some frosts in winter then some stinking hot days in summer, compared to the coastal areas where the sea temps moderate everything. But nothing like the heat you must get up in Darwin. And we also don't get as cold as the South Island, where they get snowed in which looks pretty but in reality is a pain.

So that's good to know re repotting, I was hoping it wasn't a total no-no as I doubt it'll last until the "ideal" time. Guess if it bombs then I could buy another around that ideal repot pot time and repot it then. And grump and grizzle about the cost of the dead plant for a while... Hopefully that won't happen!

With soil like that, I'd repot now. By spring, it may already be at death's door. In which case, it would be less likely to survive the repot.

Okay, repotting it is. Million dollar question now is what mix to put it into. For the other calathea, the rotting spider-mitey crispy-edged one, I used my first ever attempt at the 511 mix, and while the process went pretty well it has been very slow to do anything since. It never wilted or got worse, just sat there a bit splayed and wobbley and dull, not lifting it's leaves at night. There IS finally a new leaf coming so hopefully it's turned the corner.

But while waiting for something to happen I did more reading and I found that some people feel calatheas aren't so happy in this mix... By no means am I blaming it for anything - the plant was weakened anyway and then had to cope with me blasting it with sprays for spider mites - and if anything you could say the mix is playing a big role in its survival so far.

However... What do you guys think? Use same mix? Tweak it? These plants are completely new to me so any advice or experiences is appreciated. Thanks

My Calatheas are in the garden in a sandy/silty soil that I brought into my place. The two species that did the best for me were C. metallica and C. lancifolia (yours). The metallica has spread a lot and into spots far from the original plants, so I suspect seed. The lancifolia hasn't spread at all, but it's planted too near a large Ficus and is being choked out by roots. The tree roots help to keep the soil well drained, but they also soak up all the nutrients. That's probably why it's not doing as well as the metallica. The other thing that doesn't help is we have Bush Chooks here coming through regularly digging up mulch and often plants with it. Of course, in the garden the plants don't get fertilised regularly either.

Looking at your conditions I'd be inclined to keep the potting medium light and free draining. Especially as you're in winter. You're better off to water more frequently in a soil that doesn't retain much moisture since you're in the cooler time of year. If you can give it rain water that would be best. Town water gets a lot of chemical additives put in and isn't oxygenated as much as rain water. I think your only major issue will be water retentive soil. So I'd make sure the soil is the opposite, and then check and water it more frequently.

Robin, insufficient humidity could be a big part of the problem. Spider mites are often an issue in low humidity situations. The pathogens and predators that would otherwise keep them in check can't handle really low humidity. Also, you mentioned "crispy edges" which can be another low RH tell.

'' (BTW do I just put my zone in by editing my name on my profile?),''

Curiously, putting the zone in the name seems be much easier. But, I once read somewhere that there was some restrictions on name change so perhaps one should use the profile. Now, I have been no help at all have I?

tropic - yes I definitely want a more free draining medium, but maybe a bit more organic than straight 511? We are on rainwater, so the only chemical additives are from Dyna-gro :) Your garden sounds interesting!

albert - nooo, you've not been no help, just hardly any... Joking! Points for trying too ;) It's kinda what I thought so I may as well just try to edit my name.

paul - yes I wondered about that when my roseopicta started declining after I'd had it about a month, but that was about 4 months ago when the humidity was in the 70's (I checked this by plugging our DEhumidifier in and looking at the reading). Now that the underfloor heating in on as its winter, it's in the 50's. What I mean is the problems started when the humidity was higher.

After her full repot into 511 a couple months ago, and multiple spider mites treatments, she has just sat there sat there sat there... But now! We have a leaf spike plus better colour & perkiness of the remaining leaves, so I'm holding my breath to see what unrolls. Hoping for an unblemished vibrant leaf. Will come back to the drawing board if not...

These are pictures from yesterday, on the mend.

Just testing to see if I've managed to edit my user name

Nope

Found a potato! Was NOT expecting that! Not quite like this anyway.

So I rinsed and I rinsed, getting most of the soil off, down to the "problematic" netting plug

That came away a bit better than I thought, snipping away with nail scissors

Then, realising I didn't know WHAT to do with these, I just put it in a slightly larger pot with new mix. The netting is gone, (most) of the old mouldy soil is gone and the mix should drain better. So hopefully threat of rotting right now is gone (which is why I did all this now, in our winter)

What do I need to do now?

One week later and so far so good. Didn't wilt & leaves still lift at night, not quite as high and tight for the first 3-4 days but back to normal now. Mix is drying out faster than I thought it would so presumably that means roots are working. And no sign of white mould yet. Happy with that for now.

It's looking good.

Watering 5:1:1 mix is different than watering a water retaining soil because, well, it doesn't retain as much water. Water the entire surface very slowly until 10-15% of the volume of the pot has drained out. I usually give my pots with 5:1:1 mix another round after 15 minutes or so, especially since they went outside in 15% humidity and 100 degree temperatures.

Having to relearn judging dryness too - usually when surface looks dry then I'll check with finger then when that feels dry I'll lift up pot to see if feels light. It's different with these different mixes. Am using a wooden cake skewer - as per this forum - to help get a feel for it again. Thanks.

the new soil looks like it should drain very well... doubt you'll suffer root-rot with that mix!

just an fyi, sometimes plants come into the greenhouse with a bit of white mold on the soil surface caused by shipping conditions, they're often wrapped in plastic sleeves and packed in boxes for several days, usually scraping the mold of and allowing the soil surface to dry a bit takes care of the problem, obviously you had a more complicated situation than that but sometimes that's all that's needed

That's a good point.

Happy update : two months later, several new leaf spikes like the one to right of centre, and not a hint of mould :)

Hi I know this is an old thread but do you mind sharing what your soil mix used was? I am also repotting a calathea (Dottie) with mold and first time repotter here! Thanks so much!