Many people are very surprised to learn that the answer is yes. While you can use PVC pipes or lightweight aluminum or PVC fittings to create a container, they do not provide good distribution of sunlight. Thus your plants will not receive the required light to grow properly. However, a good quality greenhouse can be designed with sufficient greenhouse beams and UV reflectors.
You should also consider the type of plant you intend to place in the terrarium. Will it be herbaceous plants such as herbs, such as oregano and Rosemary; composite ones such as nettle, fennel and alfalfa; aromatic and woody plants such as lavender, passion fruit and cleavers; or vegetables, such as carrots, spinach and cabbage. You will need to take this into account when planning your terrarium design.
You also need to think about how much water will be dispensed through the perforations in the sides of the terrarium. There are two types of terrariums – those that have free draining holes, and those that have solid surface drainage. The free-draining variety is usually made from glass and plastic and allows water to drain out freely. The solid surface variety has holes in the bottom and sides. Both types will be suitable for fish tanks containing freshwater plants.
How much sunlight will the plants get? Some species of tropical plants only need a little bit of sunlight to grow, so adding artificial lighting will not be necessary. If your terrarium is going to have plants that normally require more sunlight than your home gets then you will need to purchase an additional, larger terrarium. This will allow more plants to get the sunlight they require.
What temperature of water is needed? Water temperature will depend on the species of plants you are adding and how many are being kept inside the terrarium. Cold water will provide a lower level of light and oxygen and warm water will provide a higher level of light and an enriched environment for the plants. On warmer days the plants will be more sensitive to changes in temperature and may freeze or die if too much warmth is introduced. On very cold days, however, there will still be enough light and warmth for the plants to survive.
Do closed terrariums require sunlight to survive? It really depends upon which species of plants you are using. Some require very little light, while others are extremely sensitive to sunlight. Some plants grow better with the sun coming from the top, whereas other plants grow better at the bottom of the terrarium. The best way to answer the question, do closed terrariums require sunlight?, is to do a little research.
If you do not want to purchase special UV lamps or plan on keeping your terrarium in a location where there is no sunlight coming in, there are ways to simulate the natural sunlight. One way is to place a couple of six-inch wide pieces of cardboard on the bottom of the terrarium. You can also place some moss on top of the cardboard. These will act as additional insulation and will help keep the temperature regulated. Another way to heat the terrarium without going through the trouble of building an expensive glass greenhouse is to boil some water inside a pot. This method will not have immediate effects but over time will increase the temperature of the terrarium.
Once the terrarium has been established, as long as there is good water and the plants are receiving all of the nutrients they need, there is no real concern about the sunlight requirements of the terrarium. There will be no need for any additional heating, artificial lighting or greenhouse gases. However, it is a good idea to check the pH and acidity levels of the water regularly. These conditions can change over time due to exposure to various environmental conditions. This is particularly important when repotting your plants from time to time.