Tightly sealed flask

After one (1 ) week, I observed that my homemade sowing medium is free from contamination, thus I plan to sow my orchid seeds. My question is, should I seal the flask tightly? What happened to the cultured inside the flask if there is no air/oxygen? Anybody can advise me what to do.

For initial protocorm developement no oxygen exchange is necessary. I only add a "breather" when I replate. I have some mother flasks that have original plants that are almost 2 years old. They still look fine. I have opened them only to remove plants for replating then closed again with original lid.

Thanks for the information. I wondered about this before and thought maybe they made their own oxygen since most are sealed up to keep our pollutants.

Cheers,
BD

i've been under the assumption it's carbon they need and i thought that's what's up with the charcoal in the medium... what do i know tho, my only attempt at flasking successfully grew disgusting fuzz in large quantities.

...anyone need some fuzz?