When you’re starting any kind of construction process, whether you’re building a pool, a house, or a terrarium, the foundations are the most important part of the project. They’re what everything else is built upon, and if you skimp out on the foundations, your project is almost guaranteed to fail eventually. This is definitely true of terrariums, except that instead of concrete and wood, the foundations of your terrarium are the soil, gravel, stones and other aggregates you use as the base for your plants.
Take the time to ensure you create a good drainage area at the bottom of your container to ensure that your plants roots don’t get drowned in case you accidentally overwater them. It’s pretty easy to do, and if you’re careful, you don’t have to buy anything (although sometimes its easier, and if you’re at all grossed out by insects, buying potting soil and pea gravel is definitely your best choice – more on this later.)