Page 40 - Tài liệu cây cảnh Bonsai4me Bonsai Basics

More worryingly, the dead roots start to rot. Naturally occurring bacteria are

able to colonize the dead tissue and in very wet composts are able to thrive. As
the root system continues to die back from the effects of overwatering, the root-
rotting bacteria are able to spread throughout the root system and slow (if not
completely stop) the ability of the tree to seal the remaining live root-tips.
Gradually the live portion of the root system becomes smaller and as it does it is
able to support less of the visible top growth of the tree.
Foliage on the tree will start to yellow and drop; smaller branches will
shrivel and die back. As the live portion of the rootball becomes even smaller, it
is eventually unable to support the primary branches and the trunk, causing the
tree to die.
Rootrot is often only detected at repotting time in Spring. Rotted roots will
be found to be black and will disintegrate when touched. The only reliable way
of stopping rootrot is to cut away all dead areas of root.
How Often Should I Water?

As has already been discussed, it is important to avoid the effects of
underwatering and overwatering. So how do you water a bonsai correctly?
Firstly, NEVER water to a routine. Simply watering on a daily basis without
first observing the condition of the bonsai soil is often carried out by beginners
following the advice of well-meaning bonsai retailers. Bonsai can indeed require
water on a daily or even twice daily basis, particularly in hot weather or early
Spring. However, watering to a routine commonly leads to permanently wet
compost at other times. If the compost does not lose some of its moisture content
between each watering, it means it is permanently wet, leading to problems
associated with overwatering.

Instead, trees should be checked routinely (at least on a daily basis), so their
water requirements can be observed and they can then be watered when they
actually require it. The surface of nearly all bonsai composts change colour and
appearance when it starts to dry out. With careful observation, it is always
possible to tell whether or not the compost surface is dry or not. This can take
anything from 12 hours to a week or longer after watering, depending on a
variety of factors such as the surrounding ambient temperature, plant vigour, pot
size and whether it has rained or not. In the UK, trees tend to need watering daily
during the Summer but with lower temperatures and increased rainfall during
Autumn, Winter and early Spring, watering needs can change day by day. Never
assume that because it has rained your tree has received enough water
particularly during the Summer. Often, it only rains enough to wet the upper
layers of the compost.