At 09:14 PM 6/30/04 +1000, Andrew wrote:
Hi everyone.
New to the Newsgroup, and been into Bonsai for about 5yrs.
But recent reading has left me a little confused.
Some books state that when root pruning at end of winter/start of spring, to
also top prune once you have repotted. Equalising the top to the bottom.
However other readings have said to allow a month between root pruning, and
top pruning. With root pruning being first, and doing them too close
together can stress the plant.

Andrew

So much for the books. This situation points out the dangers of using 'cook
book' solutions rather than understanding the physiology involved. Since
the writers of most books are artists first and horticulturists second, the
latter often gets short shrift.

Thus it is for the 'rule' that you should top prune the same amount as you
root prune. This practice is only for actively growing plants with foliage.
The reason is to balance the transpiration to the diminished uptake of
water by the impaired (pruned) root system. It doesn't work in dormant root
pruning and in fact is counterproductive.

When a deciduous plant is dormant, transpiration is practically zero, so
there is no need to 'balance the transpiration'. By removing top growth,
you are simply removing the mechanism that the plant needs to grow and form
new roots. All those existing buds, especially the terminal buds, just need
water to open and form a leaf or set of leaves. They already contain all
the food they need. Since this process of bud breaking is occuring at a
cool time of the year, once the leaves have formed, transpiration is low,
but the plant should still be protected from heat stress until the root
system is regenerated.

The terminal bud will not form a shoot until the roots are established
again, so the leaves just sit there working away to supply the roots. If
you cut off all these buds, you remove this little photosynthesizing
factory and force the plant to find food from other tissues to break
DORMANT buds, an energy costly process, further weakening the plant.

It's a similar situation for evergreen plants, but you must be aware that
there is always more transpiration from evergreens at low temperatures than
deciduous plants because of the existence of the leaves, so you have to
more careful about protecting them from heat stresses while the roots are
growing out. But the principle is the same, it is primarily the leaves (or
foliage) that supply the food to grow the roots.


Brent in Northern California
Evergreen Gardenworks USDA Zone 8 Sunset Zone 14

http://www.EvergreenGardenworks.com

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