1) Calcium ions cross-link the pectate/pectin molecules in cell walls,
thus stiffening them. Calcium deficiency results in weaker tissue
because of this (think soft over-ripe apple vs hard green apple). It
shows up at young tissue and can cause bud blast, cell collapse/death
at leaf tip etc.

2) Auxin (hormone) causes a change in pH that affects the calcium ions
unlinking them from the pectate chains. This makes the cell walls
softer so that the cells can grow/elongate more easily. Auxin is
progressively deactivated by light so with low light you get longer
weaker plant parts (leaves, stems, whatever). Uneven auxin
deactivation by light is responsible for your spikes turning toward
the window too.


3) Water availablility drives the cell expansion/elongation of the
individual cells. Low humidity/high water loss usually goes with high
light so you can get stunting even when there is plenty of water at
the roots.


Those are the primary interacting factors.


My spikes sometimes/often flop over when sunny weather is followed by
a couple of days of rain, especially if I have just fertilized. The
growth rate out paces the (reduced)calcium cross linking-stiffening
process even when the plant has enough calcium in it. Without the
sunny days preceding the rainy days the plant would not have the
energy for that high rate of growth. You can stake the spike easily
when it is floppy and it will eventually harden (you can also break it
off easily). That alternating weather pattern is great for leaf growth
but I cringe if a spike is forming.

The nitrate in calcium nitrate can give a short burst of soft growth
too. I accidentally-easily snapped offa maturing Cattleya bowringiana
pbulb a couple of days after applying calcium nitrate. Again, it was
after a couple of rainy days, and the plant had been growing in low
light.


hope this helps







"K Barrett" wrote in message news:KEmYc.64939$9d6.20844@attbi_s54...
Jerry,

Any idea what gives strength to catt flower stems? I've had nothing but
trouble getting them to emerge from the sheath and grow tall. Plants that
displayed well from the vendor now barely make it out of sheath, and when
they do immediately bend over an point to the ground. So its something I'm
not doing right. This year only my blues are producing nice stems (Sir
Jeremiah Coleman and Blue Boy) Everything else didn't.

I used to think it might be water pH. Before this year I used straight tap
water (8.5 - 9.0 pH) and infrequently fertilized. But this year I've been
very good about fertilizing and they are still weak.

Someone mentioned maybe too much light, so the stems don't emerge from the
sheath. Someone mentioned that commercially when catts begin to flower they
move them to a flowering table where light conditions change

So I'm puzzled. Any input from others?

K Barrett
"Clanorchid" wrote in message
...
Dear Group;

It seems that by adding calcium nitrate to your final rinse water when
cleaning CHC (or any coir product, for that matter), the ion-exchange
strips
the NaCl from the CHC much more thoroughly than does clear water.

FWIW, also gives leaf strength to Cats. and Phals. when used as a "Spring
Tonic", just as the orchids are going into their new growth cycle. We use
a
tsp. per gal spray, three times in the spring alternating with regular
fertilizing. Pretty much eliminates "black mush rot" in emerging Cat
psuedobulbs and Phal leaves.

Epsom Salts, in our experience, helps the plants deal with heat stress and
aids
in photosynthesis. Teaspoon per gallon spray, once a month. Spring (March
in SW
FL) to Fall (Late November in FL).

Jerry

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