There's no need to buy a terrarium when you can turn what might end up in the trash into a project. An old plastic bottle can make a nice ecosystem for plants and an interesting learning experience for kids. Terrariums raise the humidity around plants and can increase their growth. Layers of different materials are added to replicate the layers of earth and improve water levels around the plants. Plants in terrariums get most of their water from a reserve beneath pebbles. The water rises as the temperature heats up in the terrarium.
Clean your bottle under running water. Use hot water to help scrub the label off your bottle. Pat your bottle dry with a towel.
Measure 6 inches up from the bottom of your bottle. Mark a line above your ruler and extend the line all the way around your bottle.
Poke a hole somewhere along the line, using scissors. Cut on the line all the way around the bottle to remove the top.
Put about 2 inches of stones or pebbles in the bottom portion of your bottle. Excess water will drain into this section and then rise again as the temperature in the terrarium increases.
Add a 1/2-inch layer of charcoal over the pebbles to purify the water as its flows up and down between the reserve and soil.
Put a 1/2-inch layer of moss over the charcoal to separate the soil from the rocks. Add enough soil to fill up to 1 inch from the rim of the cut bottle bottom.
Press six seeds 1/4-inch deep in the soil. Add enough water to moisten the soil. Place the top part of the bottle over the bottom portion to hold in the humidity.
Water your terrarium once a week to moisten the soil. Thin the seedlings when they get their second set of leaves so that only two or three plants remain in the terrarium.