so after they've all germinated I guess they don't need a lot of humidity?
You'd think that, wouldn't you. But you'd be wrong
![Shocked :shock:](./images/smilies/icon_eek.gif)
Cactus seedlings need fairly high humidity and protection from direct sun. Weird, huh? In habitat they would get this by growing partially buried between stones or under other plants.
With low humidity, the tiny roots will struggle to keep the plant hydrated. Either you will need more water which runs the risk of rotting the seedling, or the plant won't grow very fast.
Direct sun will burn most cactus seedlings, so you'll need artificial lights or some type of shading. Full shade is generally too dark so shade cloth or perhaps morning sun.
Opuntias and a few other species will take sun and dry air much better than other cacti.