In some foreign books you might have seen pictures of miniature gardens grown in completely closed bottles. How do the plants survive without fresh air? It is quite simple. When initially the plants are planted in a bottle, a small quantity of water is fed to them. Plants need air for photosynthesis and for respiration too. For these processes the air in the bottle provides the plants with necessary oxygen and carbon dioxide. Photosynthesis is a process by which plants manufacture food. For this, energy of sunlight is used to convert water and carbon dioxide in to sugars. In this process oxygen is liberated as a byproduct. This oxygen is trapped in to the bottle only. This oxygen in turn is used in process of respiration, in which carbon dioxide and water vapour are released as byproducts. Water vapour – which condenses into water again – and the carbon dioxide, are used in the process of photosynthesis. The cycle continues and thus the plants survive without fresh air and addition of extra water in a completely closed bottle.
The soil mixture for bottle gardens should be porous and friable. This helps in aeration of roots, which is most essential for healthy growth of plants. In an open container, we can easily loosen the soil at regular intervals to aerate the roots. It is not easy to do so in a bottle garden. Hence the porous soil is essential for bottle gardens. Prepare the soil mixture for bottle gardens as follows. 1 part red garden soil, 1 part brick pieces crushed to not more than 3 to 4 m.m. (in place of brick pcs. coarse sand, rice husk or vermiculite also can be used) and 1 part leaf mould. In case leaf mould is not available, ½ part of well decomposed farmyard manure may be used in the mixture. It is not necessary to sterilize the soil mixture as stated in many books. However, to take care of fungus and insects infection a small quantity of fungicide and insecticide should be added to the soil mixture. It is advisable that the insecticide and the fungicide be mixed in water in recommended proportions and added to the soil to make it just moist. Making the soil moist has certain advantages, First, while filling the soil in the bottle, the dust will not fly and will not settle on inside wall of the bottle to make it dirty. Secondly, to plant saplings in bottle small excavations are required to be made in the soil. If the soil mixture is dry, the soil crumbles back in to the excavated hole again and again. This is prevented if the soil is just moist.
If the bottle is big enough, a thin layer of brick pieces of about 10 m.m. dia should be laid at the bottom. This will help absorb accidental application of excess water. Soil mixture is then added into the bottle. Selected saplings are then planted in the bottle with the help of fork. (see the diagram of specially devised implements for this purpose). A small quantity of water is then fed into the bottle. After this, the bottle is closed airtight. The plants will start to grow in a closed bottle. No watering should be done again unless the plants show the signs of dry wilt.
Choose only those plants, which tolerate shade and humid atmosphere. The plants chosen also should be slow growing; as fast growing plants will need frequent pruning; for which opening of the bottle frequently will be needed. Keep the bottle near the window, where it will get bright diffused light. Hot sunlight must be avoided. If exposed to harsh sunlight, plants will literally get cooked inside the bottle.
Following plants are suitable for the bottle gardens. Fittonia, Episcia, Miniature varieties of Aglaonema, Ferns, Cryptanthus, Pilea, Pellionia and Peperomia.