I started my project because of a fascination I've had with ecosystems and being able to own one. Having a terrarium is also aesthetically pleasing. The closed terrarium I built was a native terrarium. I built it using natural ingredients found in my local area. This terrarium was free of charge except you have less control over what contents are inside of it, but despite this, you may spend some money depending on what you don't have or want.

A closed terrarium is essentially a mini ecosystem in a jar. It includes its own rain system and 'circle of life'. A closed jar is meant to be kept closed.

Having a closed terrarium requires very little maintenance.

The jar must have an air seal

Supplies

Glass jar - Any size works however, the glass should be plain glass and not colored due to colored glass filtering out light, making it unsuitable for plant growth; must have airtight seal
Pebbles - This is for the drainage layer. A drainage layer is where excess water will drain into.
Fine Mesh (Optional) - used so that only water and not soil will get drained.
Soil - This provides nutrients and supports not only plants but the whole ecosystem.
Plants - Smaller plants are more desirable for a terrarium in a jar.
Hardscape (Optional) - Adding a hardscape with any rocks or any natural objects will help add a unique and dynamic look to your terrarium

Step 1:

Step 1 - Cover the bottom layer of your glass jar with about 1-2cm tall of pebbles or rocks. Doing this will allow water drainage and prevents rot.

Step 2:

Step 2 - Add a fine mesh to allow water to drain and prevent soil from passing through. In my case, I used a cutout piece of plastic bag and poked holes through it.

Step 3: Add Damp Soil

Be sure that the soil is moist, rather than soaking. Using fertilized soil also helps with a healthier terrarium.

Step 4: Add a Plant to the Terrarium

Use any plant that will fit the jar, preferably a smaller plant that is fit for humid environments.

Step 5: Add Hardscape

Add any rocks, flowers, or anything that you would like into your terrarium. I used a rock and flowers.
Do not forget to water the terrarium before shutting the lid.

Because I am constructing a native terrarium, I do not need to add much hardscape due to the possibility of plants growing later on in the days that I own the terrarium.