We always tell people that apart from Jades and Ficus trees, Bonsai need to be kept outdoors. Even the Jade and Ficus respond to a period outside as the weather warms and the threat of frost passes. When asked why, we say that they are real trees on a small scale and need a natural outdoor environment to thrive. Today I decided to try and find out why this is true.
Transpiration:
According to Wiki, transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers.
In other words, water is absorbed by the roots from the soil and flows up the trunk to the stems and leaves. This water carries dissolved mineral nutrients essential for plant growth. Transpiration occurs when water vapour flows from leaves into the atmosphere. The leaves need this water in order to photosynthesise, converting light energy, usually from the Sun, into chemical energy that can be later released to feed the trees activities including growth. The sun and wind appear to be the main force behind transpiration.
Seasonal Changes:
Perhaps even more importantly is the need for the effects of seasonal changes on the trees. We all know that trees send out new leaves in the spring and some trees lose their leaves in the winter but why do they know how and when to do this?
Apparently trees (and other plants) respond to factors in their environment especially the length of daylight and the temperature .
In autumn as the days get shorter and cooler so trees prepare for the colder months ahead by producing a stress hormone called abscisic acid. Abscisic acid closes the connection between the leaves and stems, stopping the flow of water and nutrients. This is what causes trees to stop producing the green chlorophyll within their leaves and we see the beautiful red and gold leaves on our deciduous trees before they fall off.
In winter trees enter a period of dormancy. Deciduous trees drop their leaves and evergreen trees such as conifers slow down their growth and won’t produce new leaves or needles until spring. The trees rely on the sugars produced during spring and summer stored in their trunks.
In spring the daylight hours and the temperature increases. Trees “wake up” and produce new leaves and shoots.
In summer the temperatures rise further and growth starts to slow down. The process of photosynthesis cannot function as well during the day because of the heat. All the buds containing next year’s leaves are usually set by the mid-summer.
This is very simplified but the recurring theme is that the trees respond to daylight hours and temperature. Humans regulate the temperature of their home environment to suit themselves with air conditioning in the summer and heating in the winter. We also draw the blinds and curtains shutting out the dark at night. This disturbs the natural rhythm of the tree confusing its natural cycle. Without natural light the leaves will change to maximise the light it is getting and eventually look “messy”. Even light coming through a window is not as good as full exposure for the process of photosynthesis and transpiration. Without the change in temperature along with changing light a tree can’t tell and respond to the change of season. Without a period of dormancy a tree will slowly weaken and die. As stated at the beginning, Bonsai trees are living, growing normal trees and therefore need the natural environment the same as their larger counterparts.