Jaybizzle wrote: ↑Wed Jul 29, 2020 3:47 pm
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.