Normally seedlings do not grow that fast and a container like this is fine As you can see there is enough room for them to grow taller But sometimes there is no time or not the right time to replant or they grow faster than expected Now here is another case, where the seedlings start touching the lid That is not what you want as moisture may collect at that point And the seedlings do not like that and can get moldy at that spot There is an easy way to solve this particular case by putting the lid upside down That will give some extra room for the seedlings We could have used a bigger container of course, but they take more room However lots of space to grow taller Now these ones (often succulents not being cacti) can grow pretty fast They will grow rapidly out of the container In case i don’t want to replant (no time or just lazy) i will use another container as a lid So they will be happy for a while So just a small trick, but maybe helpful to you