Re: cult:Cutting Fans /Yellow leaves

John--not "jump all over you" but there is a good physiological reason for
cutting back fans when transplanting (the "more energy to the roots" stuff
is total nonsense).  When any plant is moved, it loses much of the working
portions of its roots.  These are the fine root hairs at the very tips;
only these absorb water.  The capacity of bare-root transplanted iris
rhizome to absorb water from  the soil is initially about zero, because
nearly all of these hairs have been lost.  The plant can again take up
water when the roots start to grow (usually within a week, but full
capacity may not be restored for a month or more).  Meanwhile, water is
being steadily lost by the leaves, through tiny pores called stomata.
These pores must stay open to allow the plant to exchange oxygen and carbon
dioxide with the air, but as a consequence, they lose water at a great
rate.  This has been measured at gallons per day in a corn plant in summer.
The amount lost depends on the temperature and the humidity.  We often
transplant iris when it is hot and rather dry.  Though the rhizome contains
a great deal of water, the plants are definitely set back by this water
loss.

The bottom line-- if you cut off 2/3 of the foliage, you also get rid of
2/3 of the stomata and reduce water loss until the roots can re-establish
themselves.

One might argue that having more leaves will result in more photosynthesis,
but remember the equation:

6CO2 + 6H2O -------> C6H12O6 + 6O2

Water is required for photosynthesis; without water the plant will not be
making much food anyhow.

Cutting leaves on established plants is generally not a good practice
unless the leaves have become very unsightly through disease or drought.
Old leaves should be pulled off, not cut, and burned or disposed of away
from the garden.  I've found that leaf spot can be controlled by a single
early spraying of a fungicide and then by careful cleanup. particularly in
fall.  Fungal leaf spot spores winter over on old iris leaves.

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(804)223-6172
FAX (804)223-6374
email<bills@tiger.hsc.edu>
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