A common misconception about Bonsai trees is that they should be kept indoors. Most trees should be placed outside, exposed to the four seasons, with temperature changes and a relatively high humidity.
Outdoor Bonsai care
You have a garden or a balcony and can keep your Bonsai tree outside, so you want an outdoor tree. Which one?
The most important thing to consider is which conditions you can offer the tree and which species can live under these conditions. If you choose a native tree this is always a good idea, but keep in mind that many frost-hardy species need frost protection when they are planted in shallow containers.
Your local climate
If you live in a region with subtropical or mediterranean climate, you can grow many species outside which cannot endure frost, but some species must be protected from the heat and intensive sunlight.
Olive (Olea europea), pomegranate (Punica granatum), fuchsia, Chinese elm (Ulmus parvifolia), mulberry (Morus), corkbark oak (Quercus suber), Chinese privet (Ligustrum sinensis) are well suited. The Japanese maple (Acer palmatum) and trident maples (Acer buergerianum) can grow well if the winters are cool enough that they can go into winter dormancy. Asian hackberry (Celtis sinensis), Japanese black pine (Pinus thunbergii), bald cypress (Taxodium distichum) and some mediterranean juniper Bonsai species can also thrive in a subtropical and mediterranean climate. Cherries (Prunus), apples (Malus) and other species which need a cooler climate will most likely not grow well.
Regions with a temperate climate are good for many species, especially most of the nice imported Japanese species can be grown successfully. Subtropical and mediterranean trees can also be chosen if they can be protected from frost, in a greenhouse for example.
In a maritime climate with moist summers you might need very well-draining soil and some species which need full sunlight might not be perfectly happy.
In a continental climate with hot summers and cold winters you will have to provide semi-shade in the summer and good protection against frost if you don't want to be limited to a few very hardy native tree species.
Outdoor Bonsai trees; a Juniper, Pine tree and Japanese maple.
Conditions specific to your balcony / garden
It is important to also consider the special conditions in your garden or on your balcony. If you have full sun all day you can choose from a lot of species, but you might need some shade nets for sensitive species, especially if the Bonsai trees stand in a paved place surrounded by walls. A garden with grass, shrubs and hedges can make a big difference because the air humidity is much higher most of the time.
If you live in a region with constant winds your trees need more water but will not so easily be infected by pests and fungal diseases.
Should you have a very shady garden or a balcony facing north or east there are only very few options. You could try a yew or a false cypress but although they might survive they won't be perfectly happy. Maybe you can do something to get more sunlight into your garden (chop down some large trees or shorten tall hedges) or move somewhere else...
Your personal taste is also an important thing to consider, of course!
Some people love flowering trees like the azalea or dream of an apple Bonsai with tiny fruit in autumn, others like junipers or pines best. If you want to acquire a very special species, please get well informed first if it can live in your climate and in your garden or what you need to provide the conditions they need, like a greenhouse for winter, shade nets or an especially sunny corner. Should this be impossible, please don't buy the desired tree. It is no fun at all to watch it get weak and sick and finally die.
Outdoor Bonsai tree care
Caring for an outdoor Bonsai tree is different from that of normal potted plants. The main reason is that Bonsai trees are planted in small pots and therefore have limited storage for nutrients and water. More important is that Bonsai trees from temperate climates need their period of winter dormancy, but most species need some protection from frost and strong winds during that time.
Specific care of outdoor Bonsai species:
Most outdoor Bonsai trees need sunlight for at least a few hours a day. Their internodes and leaves will grow too large otherwise and they get prone to pests and diseases then. Most conifers should be placed in full sun for healthy growth.
On hot days and in a paved place surrounded by walls the trees can suffer from low humidity. You can increase humidity near your Bonsai tree by placing it on a humidity tray filled with water and by misting your tree a few times a day. What also helps is to wet the shelves, floors and walls around the trees.
3. Watering and fertilizing
The most important rule is; never water on a routine. Monitor your tree and only water when needed. This can be once in three days or several times a day, depending on the weather, species and size. Please read the Bonsai watering and fertilizing pages for more detailed information.
Outdoor trees can endure high temperatures as well as very cold weather if they are cared for properly. It is important for most species to provide protection from strong frost in winter. In spring, when the new leaves emerge, take care that the trees are protected even from light night frost.
To summarize, make sure to select the right tree species and take into account the specific care guidelines for outdoor trees, and you will do just fine!