Seeking help from everyone, what kind of bacteria is this and how to deal with it?

[C And D]

Rather than the baggie method, I use the container method, that way I can spray down the seedlings with chinosol anytime any algae or fungus starts growing. Once the seedlings are big enough, you can take the lids off, or leave agar to encourage drying.
Also, spraying the seeds once in a while with sterile water washes off growth inhibiters, so you get better germination.

I haven't been able to grow Aztekium or strombocactus from seed, and I think the baggie method may be better suited for these extra slow species.
Just leave the sterile pot sealed in the bag for a couple years, until they get big enough to grow normally.

[C And D]

To the specific issue for the thread.

You should spray down your seedlings using a fungicide/antiseptic

See if you can get Physon 20 where you live
that should work

[Tom in Tucson]

After using H₂O₂, how long do you wait to see if it's effective? In the past I've used Daconil, but there seems to be some anecdotal evidence that it's use may inhibit further new germination.

Most important property of H₂O₂ is that it's totally harmless (actually it might be beneficial) to seedlings. With some types of fungi/mold I had excellent results, while some varieties required consistent repeated treatment in combination with regular ventilation.
Best policy, of course, is to attempt avoiding infestation at all which requires rigorous preparation. For very small and slow growing seedlings (e.g. Aztekium, Blossfeldia or Strombocactus) this is the only way to ensure any success.

After using H₂O₂, how long do you wait to see if it's effective?" a day and it often doesn't work the plants will die by then. Best to avoid fungus if possible I tried strombocactus in a baggie and they all rotted , I don't use baggies much anymore . Will try again in the spring no baggie and I should have used H2O2 on the seeds then rinse them that's often where the fungus starts. Dry air helps BUT the seedlings really slow down if they are cactus seedlings no effect on Mesembs as far as I can tell.

Thank you both for the sage advice. I haven't been doing any preliminary procedures prior to starting my seed because I've been under the somewhat esoteric impression that the beneficial organisms in my custom soil mix would eventually be very important for the newly developing root systems. I suppose if a high percentage of newly emerging seed embryos are going to die as a result of my usual procedure, perhaps I will at least take extra precautions with both seedlings which have either been recalcitrant, or with untested species that are either very expensive and/or are exceedingly hard to obtain.

[keith]

"the beneficial organisms in my custom soil mix would eventually be very important for the newly developing root systems"

Probably crowds out the bad organisms. For a couple years I was having terrible luck growing cactus from seed or just growing them at all until I changed back to desert soil . I guess if you use store bought compost you better microwave it ? I can grow tiny lithops or conophytum seeds without a baggie but maybe not strombocactus .

[Tom in Tucson]

"the beneficial organisms in my custom soil mix would eventually be very important for the newly developing root systems"

Probably crowds out the bad organisms. For a couple years I was having terrible luck growing cactus from seed or just growing them at all until I changed back to desert soil . I guess if you use store bought compost you better microwave it ? I can grow tiny lithops or conophytum seeds without a baggie but maybe not strombocactus .

One point you made about the use of desert soil that is the apparent reason for your eventual success ratio, is interesting For along time I assumed that the reason I was getting a higher yield was due to my use of fine gravel that I had collected in the Colorado Desert washes near Anza-Borrego., was either due to it's superior drainage or to the trace elements which had drained into the channels which created the gravel were responsible for my successes. Now, although I still think that the reasons for my assumptions were at least partially valid, the possibility that the native microorganisms also play a significant role in my trials thus far (in the last several years) may actually be the most beneficial component. Comments are encouraged.

Further research either needs to done to assess my current theories assumption, or if this has already been performed, I'd like to read the methods used., and the conclusions reached.

[Steve Johnson]

One point you made about the use of desert soil that is the apparent reason for your eventual success ratio, is interesting For along time I assumed that the reason I was getting a higher yield was due to my use of fine gravel that I had collected in the Colorado Desert washes near Anza-Borrego., was either due to it's superior drainage or to the trace elements which had drained into the channels which created the gravel were responsible for my successes. Now, although I still think that the reasons for my assumptions were at least partially valid, the possibility that the native microorganisms also play a significant role in my trials thus far (in the last several years) may actually be the most beneficial component. Comments are encouraged.

Try this:

https://askabiologist.asu.edu/explore/desert-microbes

I don't know if what you learn from the article could be applied to better success with growing cacti from seed, but interesting anyway.

[Nino_G]

Role of the microorganisms is also mentioned in the famous "The Stone Eaters" article. Apparently, desert cacti are symbiotes with variety of microorganisms which produce enzimes that are able to "dissolve" rocks, i.e. make the nutrients from the rocks available to the plants. Cacti in return provide food for the microorganisms in the form of photosynthesis products (sugars).

[Tom in Tucson]

Role of the microorganisms is also mentioned in the famous "The Stone Eaters" article. Apparently, desert cacti are symbiotes with variety of microorganisms which produce enzimes that are able to "dissolve" rocks, i.e. make the nutrients from the rocks available to the plants. Cacti in return provide food for the microorganisms in the form of photosynthesis products (sugars).

I recall reading that article a few years ago. What I gleaned from it at that time was that symbiosis does play a role in the assimilation of various molecules acting somewhat like a diluted fertilizer.

Getting back to my original concern for using any solvents (or high temperatures) that might destroy beneficial microbes as a means to eradicate detrimental organisms, I'm now more inclined to only resort to total sterilization only if it appears absolutely necessary. What little evidence that seems to exist, apparently supports my assumption.

[greenknight]

You shouldn't heat the potting mix enough to completely sterilize it, more accurately you pasteurize it - hot enough to destroy fungal spores and weed seeds, no hotter than 140f - 180f is needed. Enough heat to sterilize the soil totally will not only eliminate beneficial microbes, it can produce toxic substances that will have an adverse effect on your seedlings.

[keith]

You can also water your soil mix in the pot and leave it out in the direct sunlight for a awhile ( weeks ) before planting cactus seeds. And Make sure your seeds are clean before planting .

Store bought soil mix works pretty good for tomato seeds, etc. I don't like it for cactus seeds.

[Steve Johnson]

Has anyone thought about potting sand? Aztekium123's problem is mold, not bacteria, and IMO mold spores probably wouldn't survive in the sand. What I have in mind is putting a thin layer of potting sand over one's substrate of choice. When the seeds in the sand layer germinate, their tiny roots can start growing down into the substrate. Try something like this:

https://www.amazon.com/Original-Ingredi ... hdGY&psc=1

Unfortunately I don't have enough growing space to justify growing cacti from seed, but if I did, I'd definitely give the idea a shot.

[Aztekium123]

Has anyone thought about potting sand? Aztekium123's problem is mold, not bacteria, and IMO mold spores probably wouldn't survive in the sand. What I have in mind is putting a thin layer of potting sand over one's substrate of choice. When the seeds in the sand layer germinate, their tiny roots can start growing down into the substrate. Try something like this:

https://www.amazon.com/Original-Ingredi ... hdGY&psc=1

Unfortunately I don't have enough growing space to justify growing cacti from seed, but if I did, I'd definitely give the idea a shot.

I have previously experimented with using sand on the surface of the soil in the basin. But shortly after the seed sprouts, some algae like moss will grow on the surface. For varieties with larger seeds, this is not a problem. For varieties with smaller seeds, such as Aztekium, Blossfeldia, etc., they are submerged by this algae before they grow up. Then they couldn't breathe and grow normally, and eventually disappeared.

[Lolavy]

Has anyone thought about potting sand? Aztekium123's problem is mold, not bacteria, and IMO mold spores probably wouldn't survive in the sand. What I have in mind is putting a thin layer of potting sand over one's substrate of choice. When the seeds in the sand layer germinate, their tiny roots can start growing down into the substrate. Try something like this:

https://www.amazon.com/Original-Ingredi ... hdGY&psc=1

Unfortunately I don't have enough growing space to justify growing cacti from seed, but if I did, I'd definitely give the idea a shot.

Sadly, this did not work for me as I recently lost 16 seedling pots to a mold that made its way up from the felt (autoclaved before using) covered drain holes in the bottom, and worked it’s way up to the top. These pictures are after a 24 hour soak in hydrogen peroxide and you can still see some of the moldy spots. I ended up transferring the baby seedlings and the top layer of sand to a new pot (last photo), and I’ve had to spray the top of the container everyday to every other day for the last two weeks to keep the continually emerging mold at bay. Maybe if it was a thicker layer of sand? But I can for sure say that mold is not daunted by a thin layer of sand on the top

[Jangaudi]

The idea of the top layer of sand, is that it covers the organic material in the sowing substrate, preventing the mold from growing, so you'd need a somewhat flat surface for it. A good substrate to start with is also important. I use a sifted fine gritty mix with a bit of organic material inside, not too much. And I sterilise the pot before ( I use glass jars these days. ) Draining holes are not needed when going sterile. Some of my seedling stay inside a whole year sometimes. I think it's important to choose the style of sowing, either go totally sterile, in closed containers, or sow natural, in fine gritty mix, with a top layer of sand, or other non organic substrate, and leave enough ventilation.

[Steve Johnson]

I'm only able to come at this from a theoretical standpoint, but here's an idea:

• 1-2 mm pumice as the substrate.

• A layer of potting sand completely covering the pumice, but not too thick. That'll be the seed-sowing layer.

• Mist with very dilute fertilizer -- just enough to moisten the potting sand and pumice without accidentally drenching it.

Organic material in the substrate invites mold, so a purely mineral substrate with a layer of potting sand doesn't give the mold anything to feast on. Cactus seedlings need very little in the way of nutrients, so I think a basic NPK fert is quite sufficient. Just to give you an example, I use General Hydroponics FloraMicro 5-0-1 and FloraBloom 0-5-4 diluted at 1/2 tsp. per gallon for each fert. If I used them to grow cacti from seed, I'd dilute 1/4 tsp. instead -- that works out to be 24 ppm N. A misting with these very dilute ferts should last the new seedlings a pretty good while. Could it also cause a mold problem? Maybe for growers using the baggie method or something similar, but probably not if the seed-growing container is open on top. There's only one way to know -- try it.