Watering

The closed terrarium normally will not need water for 4 to 6 months, or when fogging on the sides stops, or when plants wilt.
Open terrariums need watering occasionally, but not as frequently as other houseplants.
A dish garden, unless it is the desert type, will need frequent watering.
It is important that waterings always be light. Excess water is almost impossible to remove; better a little too dry than too wet.

Light

A terrarium, open or closed, should not receive direct sunlight.
The dish garden, however, which contains plants needing bright light, may be placed in direct sun.
If there is low light, add artificial light. A 100-watt bulb placed close to the terrarium or fluorescent tubes placed over the terrarium up to 16 or 18 hours each day.
Plants receiving light from a window gradually will face that direction. To keep the terrarium attractive from the desired view, turn it occasionally to keep the plants growing normally.

Pruning

Many plants in a terrarium will gradually outgrow their limited space.
Pinching out tips before plants become too tall results in better growth than severe cutbacks.
Be sure to remove all vegetation trimmed from the terrarium.

Fertilization

Since plants in terrariums should not grow rapidly, terrariums seldom need fertilizer.
If after the first year the plants are yellowish and seem to lack vigor, change out the top layer of soil.