Page 64 - Tài liệu cây cảnh Bonsai4me Bonsai Basics

Chapter 10 Why Repotting is Essential to Bonsai

As plants of all kinds grow, their root systems become larger and more
extensive in order that they can supply their ever-expanding canopy of foliage
with the necessary quantities of water and nutrients. Trees and shrubs grown in

the ground can have root systems that extend beyond the shadow of their own
foliage canopy in a search for water and nutrients.
On the other hand, containerised plants are limited by the size of their pot as
to how far they can extend. They need to be constantly supplied with food and
water on which to survive. Their root systems however, continue to grow in
tandem with their leaves and branches above the surface of the soil.
After a period of time that varies between different plants and plant species,
the root systems of all pot-grown plants fill their containers, and become 'pot-
bound'. Under these conditions, new fine feeder roots that are so essential to the
uptake of water and nutrients in a plant have little room to grow, the soil
structure deteriorates and the plant starts to suffer.
With an ordinary pot-plant, the solution is to put the plant into a larger
container which allows room for new, fresh soil around the rootball. With a

bonsai, the aim of repotting is the same, to allow fresh soil in and around the root
system so that it can continue to form fine feeder roots and so that fresh soil can
be introduced around the root system. However, with bonsai, the container, and
more specifically, the size of the container is not only part of the design but its
size is specially selected to suit the tree. For this reason, bonsai are rootpruned.
A side effect of rootpruning is that it increases the density of the root ball.
From every root that is trimmed, a number of new roots will emerge from the
root-tip that was removed. As the rootball is repeatedly pruned over the years,
the rootsystem becomes denser and denser. Within a well-developed rootball,
dozens of fine feeder roots can occupy the same volume of soil that one
unpruned root may ordinarily use. So though the size of the rootball is regularly
reduced, the actual volume of root within a certain amount of soil increases, and
sufficient to support the canopy of the tree.
Root pruning does not dwarf or stunt the tree in any way. The tree may lose a
little vigour for around 6 weeks after rootpruning, as it regenerates its root
system (this is more noticeable with evergreen tropicals such as Figs), but after

this short period of adjustment, the tree becomes more vigorous than before as
new feeder roots are able to develop in the new soil.