The title of this Blog could just be me trying to get as many search terms in the title as possible as the water movement is the same through all plants, large and small. Crafty Blogging! The only difference could be that some plants do adapt to either get rid of excess water and others adapt to try and hold on to as much water as possible. Examples of these in the Bonsai world could be conifers that have needles and scaly leaves instead of large, flat leaves. This is in part to stop water loss, but also for snow to easily glide of the leaves and branches in nature. The smaller surface area means less stomata through which water can be lost.
Plants with larger leaves (not really appreciated in Bonsai) do have a larger surface area and more stomata through which water can escape. Escaping water creates a cooling effect as these plants could grow in warmer climates like the tropics where humidity is high as well. Plants actually have to find a fine balance when it comes to the opening and closing of
stomata. These little structures have a dual function. Not only is it there for water to escape from the plant, a process called transpiration, but they are also in place for respiration to take place. That is the exchange of gasses in (Carbon dioxide) and out (Oxygen) of plants. Both of these processes are crucial for the survival of plants.
For water to move through a plant, there are two main processes taking place. The one has already been mentioned. This is transpiration and it is a pulling force. As water is lost through the leaves, more water is pulled up through the fibres (Xylem). The other process is root pressure. This is a process through which water enters the epidermal cells of the roots, move through the cells and into the endodermis layer. These layers of cells work like a “water pump”. From here the water is pushed into the Xylem. This action takes place against the force of gravity. It is helped by a process called capillarity. This is where water rises up a thin tube due to the adhesion and cohesion forces between water particles. This process can be seen when you place a thin straw in a glass of water. The water level inside the straw will be higher than that of the water in the glass.
It is important to know about these processes when applied to Bonsai. We do a few things to Bonsai that can interrupt these processes and disturb the flow of water through a plant. Also remember that the water also contains minerals and nutrients for the plant. Nutrition will also be interrupted if these processes cannot take place normally.
The first thing we do is root pruning. Not only does this reduce the surface area for water uptake, but it also reduces the root pressure to provide the initial push of water into the plant. This can also interrupt the flow of water and nutrients to a whole branch. The second thing we do is normal branch pruning. This has the effect of cutting off the water flow. Not
necessarily a problem if the whole branch is removed, but it can restrict water flow to parts further up the water channel. The third thing we do is to leaf prune or defoliate. See an earlier Blog on Defoliation. This obviously interferes greatly with the process of transpirational pull. It weakens the plant and should only be done with healthy plants.
These are things (pruning) that must be done if you want to cultivate healthy, good looking Bonsai. I make the call here to think before we do. Questions that must be asked is whether the tree is healthy, is it the right season, am I doing it for the right reasons, what am I trying to achieve and is it the right thing to do for the specific species? If you can answer these questions positively, then go ahead and cut. To maximise success however, ensure that the tree is placed in the shade afterwards and that watering is increased. Just be careful with the watering when you have partially or fully defoliated the tree. It means that there are fewer leaves to get rid of the excess water. Misting is always an option as well.
Let’s bring Science and Creativity together to create even better Bonsai with a great chance of survival.