Greetings, Ted!
Your plants want bright indirect light. They sunburn,just like we do. I would keep them in the shade, but with some sort of semireflectivesurface nearby that reflects sunlight to them without the direct burning raystouching their fair skin. I do this with many of my hardier plants.
Happy days,
D.Christopher Rogers
SeniorInvertebrate Ecologist/ Taxonomist
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-----Original Message-----
From: aroid-l-bounces@gizmoworks.com [mailto:aroid-l-bounces@gizmoworks.com] OnBehalf Of Theodore Held
Sent: Tuesday, June 16, 2009 11:42 AM
To: aroid-l@gizmoworks.com
Subject: [Aroid-l] Chlorophyll and Sunlight
Dear List,
I am always tempted to move certain of my plants outdoorsfor the
summer. My wife refers to this as having my plants go tosummer camp.
Here in the North (Michigan) many plants weaken if theylive for years
on a window ledge. My typical thinking is that a shortseason bathed
in sunlight in a natural setting will re-invigorate aplant. This
theory is sort of correct. The plants do derive a dose ofvigor once
they overcome the shock of the change.
The problem comes with the transition from one to anothercondition,
especially going from indoors to out. I see thisoccasionally
described as =E2=80=9Csun scald=E2=80=9D, which entails a kind ofsunburn, perhaps
coupled with desiccation. What this means in practice isa loss in
appearance, often including the functional killing of theexisting
foliage. While this is usually overcome by the growth ofnew, tougher
leaves, there is no doubt that sun scald is a setback.
Some experimentation will show that sun scald is morethan simple
overexposure to intense sun. It will also happen if theplants are set
out in shady areas, even in what is known as =E2=80=9Cdeep=E2=80=9Dshade. One can
also mitigate water loss as a cause by sheltering andapplication of
frequent mist. Scalding still occurs.
What is it about the outdoors that causes sun scald?
Here is an example of one of the most severe cases. Forthe past few
years I have rejuvenated my Pistia (aroids) with a summervacation
every year. By September, helped by additions offertilizer, my Pistia
are big and bountiful, harboring an abundance of smallflowers, which
indicate horticultural contentment. Over the winter therefreshed
individuals regress anew and are ready for summer camp onceagain.
When the plants are moved outside, they turn white withina day or two
of the new harshness. This is sun scald with a vengeance.To be sure,
tiny kernels of life remain at the plants=E2=80=99 centers andnew growth
starts at once. But the bulk of the leaves have not onlybeen scalded,
they have been bleached white. Within a week the formergreen leaves
have been converted to a minor remnant of white mush. Theloss of
color indicates to me that the chlorophyll has beendestroyed. It is
always surprising that the plants are not killed and thatthey are
bigger and more vigorous than ever within a month.
I have heard the theory that summer leaves grown outdoorshave a
tougher =E2=80=9Ccuticle=E2=80=9D, referring to a transparent layer thatshields the
inner goodies from harshness. I have also heard thetheory that the
leaves arising in outdoor conditions have fewer stomataon the leaf
undersides. It seems there are hardened leaves producedoutside and
=E2=80=9Chothouse=E2=80=9D leaves produced under protected conditions, presumably
allowing readier access to what little light there isindoors compared
with what is received from nature directly.
But is also seems as though the hardened leaves also havea degree of
screening power against ultraviolet (UV) rays. I assumehere that UV
is what attacks the chlorophyll.
Do we have any authorities on these maters tuning intothe list that
could comment and clear up these matters for me? I holdout hope that
there are one or two.
Best regards,
Ted Held
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