For the most part, yes, but there are times you might leave your lid off for a while. Keeping your terrarium closed creates a water cycle that keeps the plants and moss healthy. So you need to keep the lid on to keep the water cycle going. But you don't want or need a hermetically sealed container. In general you want to have a small amount of air exchange through small gaps between the lid and container. Removing the lid occasionally for half an hour will increase the air exchange and help refresh the air inside. If you added too much water to the terrarium, where you can see water collecting at the base, you will need to leave the lid off for a few hours at least to let some of the excess water evaporate. Just be sure to put the lid on again so the water cycle can restart!

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