How to Make a Cactus Terarrium

Choose a terrarium style suited to growing cacti. Select one with a wide open top and straight sides to allow for maximum evaporation. Avoid fishbowl-style containers or those with lids since both styles inhibit evaporation and will make the environment too moist to effectively grow cacti.

Acquire the right species of cacti for terrarium cultivation. Select species such as button cactus (Epithelantha spp.), sea urchin cactus (Astrophytum asterias), chin cactus (Gymnocalycium spp.) or pincushion cactus (Mammillaria spp.) since are all small, slow-growing and require little water, which will keep the terrarium from becoming too crowded and lessen the likelihood of rot from overwatering.

Fill the bottom 1/10 of the terrarium with a thoroughly combined mixture of crushed charcoal and pea gravel, which will provide drainage and keep the growing medium from souring. Make the surface of the charcoal and pea gravel mixture as even as possible.

Combine equal measures of potting soil and sharp sand, which is a type of horticultural sand characterized by coarse grains. Spread a layer of the soil and sand mixture across the top of the charcoal and pea gravel mixture. Make the two layers of equal thickness.

Remove the cacti from their original pots. Remove half the original growing medium from around the roots. Try not to break the roots when removing the soil.

Grip the cactus by the rootball using a pair of tongs. Position the cactus on the soil. Work the roots halfway into the soil by applying pressure with the tongs.

Space the cacti 1 to 2 inches apart. Position cacti of the same species closer together to give an established, filled-in look. Place taller species in the center of the terrarium.

Fill in around the cacti with the potting soil and sharp sand mixture created in Step 4. Pour the mixture through a funnel to better direct its flow. Completely cover the roots and fill in between the individual specimens.

Shake the terrarium gently to settle the soil among the roots of the cacti. Add more soil mixture if there are uneven spots.

Add decorative stones or gravel to the terrarium to give it a more organic look. Avoid placing large stones directly up against the cacti since the weight of the stone might damage the roots.

Place the terrarium where it will receive bright, indirect light such as near a sunny, curtained window or under a fluorescent lamp. Avoid very strong, direct sunlight for longer than three hours each day since it might scorch the cacti.

Water the terrarium no more than once a week. Apply 3 to 4 tbsp. of water around the base of each cactus to slightly dampen the soil. Allow the soil to dry out thoroughly before watering again.