The C and D Seed Growing Method

[Jaybizzle]

Is there any consensus about the best thing to use to prevent seedling fungus--i.e. damping off. Physan 20 versus chinosol versus hydrogen peroxide verus more hardcore stuff?

[MikeInOz]

Is there any consensus about the best thing to use to prevent seedling fungus--i.e. damping off. Physan 20 versus chinosol versus hydrogen peroxide verus more hardcore stuff?

There is no need to sterilize or use any kind of chemicals. The trend in professional propagation nurseries has been away from using chemicals. They hardly ever use it for raising seed nowadays.
Here's why...
In natural systems death of seedlings from soil or water borne root rotting diseases are very rare if not unknown. The reason is that the substrate has a balanced community of microbes most of which are beneficial to plant growth and suppressive to the pathogens.
When you sterilize a mix you leave a biological vacuum so there is a much higher chance of any pathogen to run rampant through the seedlings.
These days most seeds are raised in a mix which contains a wide variety of suppressive organisms. This means you need to include some kind of matured organic compost in to your favorite mix. Apparently as little as 10% in the mix will impart suppressiveness to the rest of the mix.
The last 3 years I have used such a mix with about 100 or so different cacti species and did not lose a single one to rot.

The notion that certain species do not like organic components in the mix is wrong. In the habitat, seeds usually germinate in a mix of the base mineral and the remains of dead plants (mosses, grasses, leaves, twigs bark etc). Later, when their roots penetrate more deeply they reach the pure mineral substrate. Even Genera like Ariocarpus and Aztekium will appreciate a small component of organic material when germinating and while they are very young. ( see the second pic here of Geohintonia in habitat. Notice the little seedling growing in the remains of dead organic material embedded in the rock. http://agaveville.org/viewtopic.php?f=2 ... &view=next )
There is no need to worry about pathogens in organic material if they have been properly treated.

After some research I found the the best materials to use for your compost is hardwood barks. This is probably because they have a high content of lignin and the decomposition (and suppressiveness) can last a long time. Some research in Australia has found some composted Eucalyptus barks remained suppressive for more than 3 years in a pot.

I make my own compost from shreaded tree prunings from my garden which contains bark, leaves and wood. Hot composted for a few weeks and then left to cold compost for a year or so turning over and over. From that I sieve out some of the finer particles and store that moist in a bag with holes for a few months.
The storing and maturing process is very important because during this time that the beneficial microbe numbers build up.
Immature compost is definitely no good.
It's probably a good idea to make up your mix, add the suppressive compost and then store it slightly moist for a few months before using it. In other words, make it this year for using in spring of the following year.

If you don't want to make your own there is bound to be someone close who does it. The local council park people probably have tones if it.
I have found this method very successful with all species including Ariocarpus, Geohintonia, Astrophytum, Pelecyphora and mamms like pectinifera and herrerae.

[esp_imaging]

Is there any consensus about the best thing to use to prevent seedling fungus--i.e. damping off. Physan 20 versus chinosol versus hydrogen peroxide verus more hardcore stuff?

I use a sterile 100% or near 100% mineral mix for seed raising. I keep cacti in sealed containers for weeks / months. I don't use chemicals and don't generally get damping off problems. When i do, I suspect it's due to fungus originating from the seed, which I don't sterilise.

[keith]

When you sterilize a mix you leave a biological vacuum so there is a much high chance of any pathogen to run rampant through the seedlings."

That's what I noticed so don't sterilize and don't grow in plastic baggies anymore but under a plastic dome for cactus. Sometimes I have to use fungicide like H2O2 or rootone powder usually with cactus seeds.

Air movement and light helps keep fungus away. So far hardest seeds to keep going are dinteranthus vanzylii and conophytum .

Didnt know about the hardwood pieces to suppress fungus that's interesting. I'm back to using allot of sand in the mix.

[Jaybizzle]

Yeah, I also believe fungus problems that I had were related to stuff on the seed coat and not to anything in the soil.

[CactiJim]

Do you think spraying neem oil on your soil mixture before sowing your seeds would be bad? Would it affect the seedlings?

[C And D]

Sterilization is only necessary for covered pots
Fungus and algae will run rampant in the humid system

I still use the above system for most of my more sensitive species

But I've also have 100s of seeds in open beds outside and inside my green house
I mix up a batch of rich soil and put it in deep flats.
cover with a top dressing gravel
Spray with Physan 20
then sprinkle seeds galore on the top

Then water with hose often, at least twice a week

Mesembs and South American cactus grow like crazy all year long

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See my Succulent Vegetable Garden Thread
https://cactiguide.com/forum/viewtopic.php?t=36823

[C And D]

Deep Flat
Using 100% Commercial Coir & Perlite
100s of mesembs

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Close up of Cereria pygmaea seedlings

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