Create Your Own Terrarium
Terrariums, miniature gardens and "fairy" gardens are quite popular projects for Do It Yourselfers, and offer a wonderful garden in a small contained space. It's perfect for people who live in apartments with no outdoor space, or people who want a low maintenance, small indoor garden for year round enjoyment.
Choosing a Container
Choose a container that is made of glass. This is important for light to get to the plants. Make sure the opening is large enough to get your hand inside to plant and maintain the terrarium. Some people choose a container with a lid, some prefer an open jar. It's a personal preference, and the only difference will be in how much water it will need when you care for it.
Plants
Choose plants that do well in low to medium light. Small versions of common houseplants are perfect, and easy to obtain. Many are available in 2" and 3" mini pots that are grown just for this purpose. Keep in mind where in your house it will go, and how much light it will get. A southern window in the winter months here in the upper Midwest will be okay for low light plants, but as you get into the spring and summer, the light will be to intense. Also choose plants that can tolerate a humid environment, and like their soil damp. Pick plants with different texture and leaf shapes, but make sure their light and water needs are similar.
If you would prefer succulents/cacti, you will need to allow for more light, as well as alter your planting material slightly.
The Base Layer
Because terrariums do not have drainage holes like standard flower pots, you will need to make sure to create drainage layers. Some people prefer to put a layer of sheet moss on the bottom of the container, but that is optional. On top of this put about 2" of small rocks (don't get them too small, you want to leave space in between for the water to drain). This amount will vary if you have a very shallow container.On top of the layer of rocks, put about 1/4" to 1/2" of horticultural charcoal. This will also help with odors. Again, some people choose to put a layer of sheet moss over the charcoal, to keep the soil from mixing with the drainage layers.
Planting Mix
Now you're ready to get down to planting! Use sterile soil-less planting mix, such as potting soil. Never use top soil, or soil from your yard. It will pack down and your plants will suffocate. Put a couple inches of the potting soil on top of the drainage layer. If you would like a more "landscape" style, you can vary the depths to create small hills and valleys.
If you are planting succulents, you will need to use a cactus/succulent mix, which contains more sand to allow better drainage.
Adding Your Plants
Using a large spoon, or your fingers, make small holes in the soil, large enough for the roots of the plants. Place in the hole, and then gently move soil around the base of the plant, taking care not to compress it too tightly, but also making sure there aren't any air pockets around the roots. Make sure not to put your plants too close together. It's also wise to avoid having them touch the sides of the container. Also think about composition---will your terrarium have a front and back? Or will you see it from all sides--if so, put the taller plants in the center, and shorter ones around it. Also, if you would like to add small decorative items like rocks or fairy garden figures, allow room for them, as well as space to see them from outside the container. Avoid overcrowding.
Caring For Your Terrarium
Ongoing care is fairly easy. Water it every week or two, depending upon how humid your home is, and how much water you put in. Don't be afraid to stick your finger into the soil. You don't want it to get too wet---it should be slightly damp. You can also look through the glass at the bottom layer and see if there is a lot of water accumulated there. Do not fertilize your terrarium---you do not want the plants to grow too fast. If you have a closed terrarium, you will need to take the lid off every few weeks to let it air out, as well as if you see condensation on the glass. If leaves turn yellow or brown, pinch them off. That is a good time to closely inspect your terrarium to make sure it has not been over watered, under watered, or invaded by common houseplant pests such as gnats. If there are bugs, gently spray with insecticidal soap. 
