Air, Humidity, and Temperature

Fresh air and sufficient humidity are as important for small trees as they are for all other plants, as well as for people and for furniture made from wood. This presents no problem during the summer; plants can be brought outside, to a terrace, a balcony, or the garden. Just make sure that they have a chance to adjust slowly to the light, air, and sun. The best way is to bring them out in small steps. Start with a few hours on somewhat cloudy days in early spring when the sun has not yet reached the intensity it has in the summer. Bonsai can be placed outside or inside, depending on the weather.

During the winter months when we turn on the heating system, bonsai need some help: 40% to 50% humidity is ideal. If you don't like electric humidifiers, put pottery trays filled with water near bonsai and on top of the heat registers. Either way, this is also very beneficial for human respiratory passages.

Another possibility for providing the necessary humidity is to place your bonsai on a tray filled with sand or gravel. Keep the sand or gravel damp at all times. Such a setup works well for plants on a windowsill that has a radiator or heat register underneath.

Humid air is very important for your bonsai because it reduces water loss by transpiration, by which might lose more water than it is able to take up through its roots if the air is too dry. If the plant loses too much water, stomates, located on the underside of the leaves, close up; the exchange of gases necessary for photosynthesis is interrupted; and the growing process is disturbed. Something similar happens when the stomates are clogged by dust. That is why giving your bonsai a gentle shower in the bathtub once a month is recommended.

Keep in mind, when buying a bonsai, that your house may be particularly dry in winter and perhaps somewhat dusty-depending on the type and the amount of heat and the type of insulation - so choose accordingly. Some bonsai plants are more sensitive than others to dry conditions; those with thick, somewhat leathery leaves lose moisture less easily and are more suitable to conditions where the humidity is low. A good example is the Ficus buxifolia. Its large, soft leaves are a sign that a great deal of transpiration takes place; such a plant needs a high degree of humidity. Lantana is another example. For this reason, anyone who has indoor plants should also have a hygrometer.

Another factor to keep in mind in many regions during the winter months is drafts. Tropical plants are particularly sensitive to them. The lower the outside temperature, the more risky it is to open the window-even for just a moment. If it is very cold outside, bonsai gardeners recommend removing plants from the windowsill before opening the window. For those of you who can't take your bonsai outside in summer, there is an advice: during the summer months, air out your house often.

When you think about the requirements necessary for your bonsai, remember that no plant was created for indoor living. The climate in the plant's native habitat must be your guide for creating a suitable environment indoors. This is particularly important when it comes to temperature. Depending on where you want to create your "green island" in your home, choose bonsai that are subtropical (cold house) or tropical (heated greenhouse).

Subtropical trees and bushes are accustomed to warm summers and cool winters in their natural habitat. When outside, they like to be in an area that is protected from the wind (get them used to the outdoors slowly). Indoors, during the winter months, they like cool locations, ideally, with temperatures from 41° to 59°F (5° to 15°C) during the day and somewhat lower during the night. A smart and sensible bonsai gardener will place subtropical bonsai on a balcony or terrace, or in the bedroom or hallway, or the staircase, all depending on the time of year.

Tropical plants should be kept warm throughout the year, because in their natural habitat they grow almost without a dormant period. They are most comfortable with daytime temperatures from 64° to 75°F (18° to 24°C), and 57°F (14°C) to 61°F (16°C) at night, the normal temperature ranges in many modern homes during the winter. Tropical bonsai, therefore, can be placed directly over a heating source during the winter without losing too much moisture if the proper air humidity is provided. What your tropical bonsai do not like are "cold feet," which happens when the area around the roots is colder than the surrounding air. This can occur if you have a stone or a marble windowsill or when cold air penetrates through small cracks.