Opuntia In Arkansas

A thousand Opuntia robusta seeds were planted on October 10 and started to sprout on October 18.  I did not expect this, nor did I expect around six-hundred or more to sprout within the next few days. The setup I have would not accommodate much more than these O robusta  seedlings so the other cultivars not showing any activity were put outside to sync with nature and maybe some will sprout next year at some point. So now it appears I'm an O robusta farmer!  One Opuntia phaeacantha 'Plum' sprouted as well as a couple of Regina Oliver Unknown and O engelmannii var. 'Texana' so they remain in the program. One day there was bare mix, the next day there were cacti. They were kept under humidity covers for a few days because I saw it done on You Tube video's... The covers didn't seem right so I tried removing them to see what would happen.  They have been off since. I see no benefit to having them if none die without the covers and