Date: Fri, 05 Jul 1996 22:14:16 -0700
From: Franc Hancock <franc@pnc.com.au>
Subject: [9441] Re: Onc. splendidum

webbjl wrote:
> Welcome to the group. I was pleased to note your interest in Onc.
> splendidum. This plant is difficult to grow here in upstate New York. I
> wondered if you could offer any cultural tips on how to best grow it? Any
> information will be appreciated. My direct email address is;
>  webbjl@crd.ge.com
>
> Thanks in advance,  Jim Webb

Hello Jim,
Here is some info which I have sent to California hope it helps

Oncidium splendidum

This plant belongs to a section of Oncidium which is characterised by
reduced pseudobulbs and leaves which have taken on great substance and in
a way taken over the storage role of the bulb. Leaves are
characteristically 'V' shaped which gives them rigidity and provides
shade..  The 'V' fold in the leaf ensures that as the sun travels through
the sky one edge of the leaf is usually casting a shadow over the leaf
surface. It needs this because it lives in hot, dry situations and must
guard all the water that it can store during the good times.  Its
environment gives the clues to its cultivation.

 The 'Mule Ear' Oncidiums and the terete leafed Oncidiums come from hot
savannas and semi-arid deserts where they grow on rocky hills and ridges.
Oncidium splendidum is from rain shadow areas of Honduras and Guatemala.
To enable them to survive these hard conditions they have modified their
structure and metabolism.  The outer layer of the leaves has developed a
hard layer of cutin to retain moisture. The leaves have also become
fleshy with water storage organs.  To add to this they have changed their
method of photosynthesis as well.   Most plants absorb carbon dioxide
from the air during the day for photosynthesis and rest at night.  In hot
arid environments this day time respiration would cause moisture loss
which could be fatal.  These orchids have modified this process enabling
them to absorb carbon dioxide from the atmosphere during the lower
temperatures of the night and to fix it in another form in the leaf cells
where it is used for photosynthesis during the day.  These plants must
experience a marked temperature variation between night and day.  They
also dislike humidity which causes the leaves to rot.  In my own
observations fungal attacks on the leaves in humid situations appeared as
blackened circles on the back of the leaf starting around the tip.  These
slowly spread down the leaf turning it a reddish maroon colour.
I grow this plant now on mounts that I make specially for it.  In the
past I have grown it in very chunky bark (about the size used for Vanda).
I would pot it with its roots exposed for about an inch this would leave
the plant looking like it was standing on stilts.  This enabled me to
lightly mist the exposed roots once a week in the dormant season and to
observe the new root growth initiating when the plant became active. 
When the plants roots are not active I only apply a light misting to
simulate early morning condensation once/twice a week.  When the new
growth starts to produce roots I increase the frequency of this misting
until the roots reach the growing medium, I then start proper watering. 
I water once every three days if the weather is sunny.  If the weather is
cloudy leave it longer till the next watering. I apply different
fertilisers at each watering at about 10% of recommended strength with
just straight water about every fourth watering.  When I water  I dunk
the plant (mix only)briefly into a bucket of water (2 gal) then take it
out to let it drain for an hour before pouring a watering can  (2 pints)
full of fertilizer/water through the mix. I grow it in half day full
sun in my glasshouse ( sun from 11 to 4.) being in the mountains I get
reguar mists and fogs outdoors, but when I was living in Sydney I grew it
outdoors all summer in full morning sun from sunrise till about 1. It
only had protection from rain.
      It hates high humidity and loves air movement.  I've achieved this
at present by placing the plant in an airstream from my fan heater through
a plenum (plenum-long polythene tube attached to end of fan heater, tube
has smaller holes along its side through which the heated air flows).  It
is winter now so the sun is low in the North(southern hemisphere), I have
a position against the side wall of the glasshouse where the sun shines
in unimpeded by the shadecloth on the roof. This position is near the
electrical control panels so is a no water area also this wall of the
house has no thermal film over it so the night temp drops lowest here.

In short give your plant less water, more air, more sun, low night temp,
low humidity.

Franc