Cold and sunlight

18 years ago

I have noticed that some of my bromeliads exposed to the morning sun get severely damaged during our cold winters and those of the same species that are shaded (but no overhead protection) will take it better. Today I came accross an old GW thread that explains it quite clearly. As I think it could be useful for others, I rewrite it here (the thread is of 2003 and has since been deleted). The author is JoeReal and he seems to understand his matter very well, the explanation only involves the basic mechanisms of the photosynthesis:

"When photosyntheticaly active light strikes the chloroplasts, it absorbs energy by exciting the electrons, these excited electrons in turn are passed on downhill through the complete photosynthetic pathway used to generate sugars and oxygen. Now for some tropical plants , the rest of the photosynthetic pathway is simply closed down or not fast enough because of low metabolic activities caused by low temperature, even if above freezing. Their specific metabolism are not best suited at low temperatures. Thus instead of the energy in the electrons being utilized to fuel the photosynthetic factory, the electrons instead create free radicals which are highly reactive and cause damages to the plant tissues. Simply put, it is short circuited because the receiver is fast asleep to pass on the burning torch and use it as fuel down the assembly.

Bring a cold-sensitive plant into the sunlight in the early winter cold morning of California. Bring also another cold sensitive plant outside but in the shaded area. The one exposed to full sunlight will surely have extensive damage such as leaf burns...."

The conclusion? It may be usefull to protect the plants from morning sun as long as it doesn't get warm enough. If it is not possible to move them, this may be achieved covering them with something that will provide shade or putting some screen between the sun and the plants.

I hope this was not too boring

Tomas

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Comments (12)

hotdiggetydam
18 years ago
The only time I have encountered a problem with this..is when the leaves are wet...otherwise mine have not suffered any damage.
Applies to any time of year
mike4284m
18 years ago
Sounds interesting but I'm not so sure. I think more tropical plants do better in shade when it's cold because they have some sort of protection. Measure temperatures with and without overhead protection and I think you'll find a measurable difference.
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avane_gw
18 years ago
Thanks Tomas, that was really helpful. I have a lot of tropical plants in my garden. Like some cold sensitive palms. And the only ones that survived the longest in my garden (we do not get frost here in Cape Town, but temperatures go down to as little as 5 degrees C, with the exceptional cases of down to 2) were the ones that does not get sun in the morning and that is the coldest part of my garden!

Japie
LisaCLV
18 years ago
That is very interesting, Tomas. I've never heard that before, and of course it's not an issue where I live, but it's good to know.
sander_s
18 years ago
My Vreisea Nova suuffered some burns last week. It is indoors behind a window that has some sunlight in the end of the afternoon.

Since it is winter over here that is very weak sunlight. It has burns at the edges of the new leafs anyway. I do not believe the elecron story somehow. Neo's in the same spot with young leafs show no damage. I will post some pics when I have the time.

Sander
tomas
Original Author
18 years ago
It of course doesn't want to explain any kind of leaf burn that may appear on bromeliads. It only says that if a plant gets the combination of cold and sunlight, some damage can be produced. I suppose it doesn't freeze inside your house :-)
Tomas
sander_s
18 years ago
LOL No frost in here Tomas!

But still my normaly in full sun Vriesea has burns. Not much but it is a shame this was a perfect plant.

{{gwi:437494}}

Weird huh? In the summer it bakes in full sun an nothing happens. And now in cooler conditions with just a bit of weak winter sun (behind glass though) I get this.

Sander
tomas
Original Author
18 years ago
It probably has nothing to do with sun. You may look at this, something similar was already discussed here and there are many good hints.
Tomas

Here is a link that might be useful: burnt vriesea
stanofh 10a Hayward,Ca S.F. bay area
18 years ago
I havent found the morning sun damage to be true.Like said above,a plant that doesnt get morning sun is most likey shaded by something that also fends of frosts.On my front porch my most tender shade plants are sheltered from light frosts AND get sunup,sunrise, sunshine.They so do best of all from the hours of direct winter sunlight for three hours or so. The same very same tenders in the shade and shelter of the backyard start to fall apart or show much stress from hours of cold shade untill noon. Quite a difference between a shade 48f and sun 48f on tropicals just to pick a temp that seems to be roughly,the turning point for tropicals.
winterlager
18 years ago
Do you let your plants dry out? Mine are mostly outdoor, in ground and hold lots of water in the cups year round. I was looking at a Blanchettiana today and it must be holding a gallon of water. My neo's never seem to flower since they are always flooded. I have some that should be ready to flower and I've tried to drain out some of the water, but it's futile. They seem to want to hold that water and unless they are in a pot, it's very hard to dump.

Anyway, the burn you show looks like dried out new leaves to me. Although, I've never seen that.
tomas
Original Author
18 years ago
Stanofh,

what I tried to explain was about leaf burn, if your plants fall apart, it looks more like rot.
Tomas
sander_s
18 years ago
That's not dried out. There is allways water in the cup.

I'm pretty sure it's sunburn, the burns are on the side the light comes from. And the plant is in a cold spot near a big cold window. 10-15 centigrade a night, maybe even colder during frost and there is a lot of water in that plant. I can imagine that stays pretty cold all day. At the end of the day that spot can get quite some winter sun.

The electron theory is an option I think.

Sander