My daughter bought a plant terrarium kit at Hobby Lobby and loved it, so we made our own at home. Here’s how we did it. First, poke holes in the bottom of the cup using a nail. Then, fill the cup with soil and add a seed or small plant. Tape another cup on top the cup containing the plant to form a dome. Then poke holes in the top using a nail. When it rains, little drops of water will drip into the terrarium and excess water will go out of the bottom.