Soil Fungus?

chaparralgirl(Sonoran Desert (CA))September 6, 2011

I've been noticing this odd, yellow-ish/rusty-ish substance appearing on the surface of the soil in many of my potted plants. The vast majority of my plants are cacti and succulents, but I've been noticing it with some of my herbaceous houseplants as well (i.e. Philodendron, croton, etc.) Tonight, I bought 3 more cacti and a succulent from my local Wal-Mart, and I noticed that ALL the cacti and succulents they had there have this stuff on the surface of the soil.

It looks like this:

(Not my photo, but that's what it looks like.)

Does anyone know what it is and (if it's a threat to my plants) how to get rid of it?

I can't vouch for the soil the plants are originally potted in, but when I do transfers/repotting, I use an organic cacti & succulent medium. A number of my containers are non-draining, but I manage those plants' waterings very carefully; the weird fungus-looking stuff is in the draining containers as well.

I try not to water too often, but even as indoor plants the soil seems to dry out really quickly (I do live in a desert), so sometimes I find myself watering ever 2-3 days. (That seems excessive to me, but I go by the moisture of the soil.) I also keep my succulents and cacti in an east-facing window (some on the sill, some on a table just below the window), so they get an abundance of sunlight, but for only a few hours each day.

Because it's scorchingly hot out, I can't open the window to allow for ventilation and air circulation; instead, I keep the ceiling fan on.

I've been watering all my plants for the last year and a half with tap water (which I JUST read is no bueno for my plants); our water is pretty alkaline (although I don't know the pH) and saline (744 ppm).

It is fairly dusty in our home (at least by my standards, anyway), and I frequently have to dust off all my plants so they can breathe. I wonder if there's something floating around in the air/dust that contributes to the weird fungus-looking stuff on the soil surface.

Thoughts? Anyone?

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It's not fungus - those are salt/ ion crystals that accumulate from soil transpiration.

Luckily cactus and succulents can tolerate it, but their health can suffer long term.

There are a few things that can be done to reverse this process. Most importantly, when you water it has to be enough that a good amount drains out through the bottom completely without any water left to sit in a saucer. This is called leaching. It is a bad habit to regularly water your plants with only a small amount of water. Ions accumulate this way.

Using neutral to slightly acidic water is helpful. Adding a small amount of vinegar to tap water seems to be beneficial. Rain water is perfect but not practical.

Finally, you must change the soil mix. "Organic" mixes work outdoors in the ground but are far from ideal in small pots, especially with cactus and succulents that grow slowly and aren't watered often.

There are plenty of discussions on this forum regarding potting mixes. If you do a search you will find many hours worth of reading.


    Bookmark   September 6, 2011 at 5:55AM
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chaparralgirl(Sonoran Desert (CA))

Salt/ion crystals! No kidding! I never would have figured that one. Thanks!

I had read in a book on succulent container gardens that you COULD maintain non-draining containers if you give the plants just enough water to keep them going. I imagine, though, that that advice doesn't allow for the pH and salinity of the water I've been using. I would prefer rainwater, but you're right, it's not practical, especially where I live. (I'd be waiting a loooooong time...)

And I never would've figured on the organic mix for indoor plants. I'll do a search for suitable indoor potting mixes for cacti & succulents.

Thanks so much for your insights, this has been a great help! :)

    Bookmark   September 6, 2011 at 6:10AM
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Unfortunately much of what you may read, especially in mainstream media and generic books, is not very helpful and sometimes completely wrong. You will learn much more from specialty material, and from this forum.

Most here would agree that a very well drained, porous, stable and inert potting mix lends itself to greater success. It allows for safe watering, without fear of rot or saturation. Ingredients like pumice, perlite and turface are readily available and not necessarily expensive. They also don't decompose over time so the soil mix is long lived and does not need to be replenished nearly as often as a mix with organics like peat.

There is much to learn. That's part of the fun.


    Bookmark   September 6, 2011 at 9:45AM
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chaparralgirl(Sonoran Desert (CA))


Thanks for your feedback. I was actually just reading a few other threads on soil that you had contributed to. I bought a few smaller bags of Uni-Gro cactus mix the other day, and looking at the ingredients now I'm debating whether or not I should return them.

Here's the list (in order):

- Pumice, Forest Products (?)
- Peat Moss
- Sand
- Bone Meal (??)
- Blood Meal (??)
- Cottonseed Meal
- Alfalfa Meal
- Earthworm Castings.

I still consider myself fairly new/uneducated about the finer points of keeping plants in general. I recognize the pumice as a good component, and earthworm castings sound reasonable. Peat moss I keep hearing not-so-great things about. Alfalfa? Forest products? Cottonseed? And what's up with the blood and guts? I know that animals/people die and their decaying bodies become nutrients in the soil (when they aren't massively preserved); is this along the same lines?

Parts of the bag are clear, and from what I can tell the soil seems relatively fine - no large wood chunks. There are also a few small holes, and the soil seems to have a hearty earthy smell. Color is also a deep, rich, dark brown/black (with the exception of the sand particles).

On the topid of "experts", what do you know about/make of Debra Lee Baldwin? It was her book "Succulent Container Gardens" where I read about keeping non-draining containers. I should note that, by and large, she does insist on well-draining soils in draining containers, but that with particular diligence it is POSSIBLE to keep succulents in a non-draining container, although it shouldn't be considered a permanent home for said succulents. Your thoughts?


    Bookmark   September 20, 2011 at 3:24PM
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Pretty much every one of those ingredients should not be in a cactus/succulent mix. The best I can say is to search this: "Gritty Mix". For cacti & succulents, this is the best stuff you can use, hands down. I use it for ALL my plants now, even tropicals, although I do modify it according to individual plants.

The next thing I'll tell you, hoping not to offend due to ideals, is that organic container growing does NOT work. Save the worm castings, compost, various types of "meals", and other organics, for your in-ground garden. Containers will never contain the bacteria needed to effectively use organic material, let alone maintain them.

Ok, on to your book, and the non-draining pots. There are a couple of reasons that it just won't work. Firstly, root rot. With no drain hole(s), how could one REALLY know that they've completely saturated the soil, but left NO excess at the bottom? Not possible. Secondly, it is essential for the long term health of ALL plants that things like salts from water and/or fertilizer get flushed from the soil and do not accumulate. A pot with no drain hole(s) will not allow ANY salts to be flushed. Other things will also build up, mainly chemicals from your water, and different minerals from the fertilizer that you use that are in excess of what the plant needs. The root rot would getcha first though. All you need to do is leave certain succulents sitting in perched water for a day, and you can kill it.


    Bookmark   September 20, 2011 at 10:50PM
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chaparralgirl(Sonoran Desert (CA))


No offense taken (or even remotely perceived *scratching head*). Like I've said, I still consider myself new and unlearned on all this stuff, so I appreciate the edumacation. :)

I will look for that Gritty Mix. Kick in the pants that ALL those ingredients are *raspberry*. I opened one bag and used a little for a few aloe pups I cut from my big aloe. I suppose we'll see what happens - though I should mention that the mix felt like it had a fair amount of moisture in it (which struck me as rather odd).


    Bookmark   September 20, 2011 at 11:04PM
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Howdy, from an adjacent desert.

I love Debra Baldwin's book on container gardening, and I have a friend who loves to tend tiny succulent gardens she plants in large seashells (no drainage.) I do think this is possible, on a small scale, for a period of time, with great care. Baldwin's book does a terrific job of kick-starting our thinking about what containers can do for plants, visually. She also has pretty good basic growing advice in the book, but I think's it's rather a matter of choice, and emphasis, and that may change for you as you continue to collect succulents.

I use a ceramic drill bit from Lowes to drill holes in the bottoms of all my pots. I'd never plant anything in a non-draining pot, but it's because I choose to have a ridiculous number of plants, and I want to stack the deck in their favor. If I accidentally overwater, I don't want to make my error be a certain death blow to a succulent friend of many years. I want them to be as healthy as possible. I just don't have the time or patience to do the very careful watering and fussing that non-draining containers demand (as cool as my friend's tiny seashell gardens are.)

With luck and great care, it's possible to successfully raise a bunch of toddlers on the edge of a busy freeway, but your success rate will be much higher, and stress much level lower, if you can move them to safer, healthier housing. ;-)

I agree with all of the advice given here. For the cacti and succulents we love, drainage is king!

    Bookmark   September 21, 2011 at 10:56AM
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With luck and great care, it's possible to successfully raise a bunch of toddlers on the edge of a busy freeway, but your success rate will be much higher, and stress much level lower, if you can move them to safer, healthier housing.

You win the prize for the best analogy of the day! :-)

    Bookmark   September 21, 2011 at 11:41AM
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hoovb zone 9 sunset 23

CG remember you have a distinct advantage (in certain respects) over most other growers on this forum. You have a nearly always sunny climate in which soggy soil is going to be non-existent, and you could probably get away with planting in straight peat (no, I don't recommend that at all) because your areas consistently low humidity is going to compensate and suck the moisture out of your mix in the blink of a proverbial eye, no matter what mix you use. You ain't in Wisconsin.

On the contrary, you may have to compensate for your mix drying out too fast for certain succulents, and your extreme heat may affect some plants in a negative way (but be great for others).

Just keep that in mind--adjustments need to be made for climate. The best place to start is to learn the native climate of each plant, and try to simulate that climate as best you can. Some plants will be easier than others.

I'm along the cooler moister California coast, and very gritty mix means I have to water daily to keep some of my plants happy. I don't need as dry a mix as Maine or Wisconsin or New York needs.

    Bookmark   September 22, 2011 at 5:08PM
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CG, firstly, about the possible offense thing, in previous threads, if someone talks anything negative about organic anything, the eco-nuts go postal. For example, one poster made a thread asking about what soil mix would be best for something, and when gritty mix was suggested, with the use of Foliage Pro 9-3-6 fertilizer, the original poster went off the deep end, reading the riot act about how bad synthetic fertilizer and soil is. So bascially, some people looking for advice aren't always looking for MY advice, or some other people's advice. But, thankfully, that's not you.

Good, now that I got that out of the way...

Hoovb makes a great point about moisture loss in your climate. Although I think he/she might have threw a cheapshot at Wisconsin. I still would advise you against the use of anything organic, and especially against peat moss. I grew in it for ages, and I never rotted anything, well, to death anyways. But, upon repotting, the peat moss mix turned into a nasty sludge, and the center and bottom of the rootballs were always gone, presumably rotted away. The healthy roots were always near the edge, where the mix dried faster. Since switching to gritty mix, I find that I have majorly healthy rootballs. To add to the luster of gritty mix, it lasts literally forever. Mind you, I do not use any pine or fir bark in mine, just turface and grit. If you use bark, then it does have a life to it, but more in the range of 5 years, verses the 6 months you get out of peat based mixes.

So, should you choose to go gritty, you may want to add more turface to compensate for your dry climate. I use a 1:1 ratio of turface and grit, and I water about once a week indoors. For plants that are outdoors in summer, it varies, but most are every other day, but that all depends on how big/small the pot is, if the pot is jammed with roots, and if it's super hot. Windy, hot days also drain the moisture.


    Bookmark   September 22, 2011 at 7:58PM
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