Many orchids can be grown symbiotically like they grow in nature. The cardboard method uses cellulose in the form of cardboard to act as a food source for the symbiotic fungi. It's quite effective for many terrestrial species, less so for epiphytes.
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Getting the seeds to grow is not hard, growing them to a large size is hard. On my first try I had a flask with over 1000 in it, but mold has taken out 98%, I am hoping I get 5 or 6 to bloom.
I have bought medium mixes from many suppliers, some with charcoal and some without. None worked well for me. I now mix my own, I use agar from the grocery store, yes I have to buy the MS, IBA, 6-BAP, NAA, PH meter, and beakers, but 90% of my plats germinate.
If the mold develops more than a couple of weeks after flasking, the problem is the flask seal. Earlier and it's a sterile technique proble.
Also if the ambient temperature varies the air in the flask will expand as it warms, pushing air out of the flask, and contract as it cools, pulling air into the flask. This may draw in fungal spores. Try to keep flasks at a constant temperature.
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