New greenhouse nightmares

[Raqsharqi]

I'm a newbie and this is my first post...other than my introduction.

I put up a new greenhouse primarily so I can grow vegetables without having the creatures of the night eat them before I can get to them myself, but I have a corner to set up for orchids. I know that's somewhat of a problem because of the different requirements of the orchids, but I suspect most of them will find one corner or another suitable in terms of light, and I have to try to keep the temperature inside to 85 or lower so as not to stew the tomatoes! I have to use misters to do this, so humidity may be a little lower than what is ideal for orchids, but even so, it will probably be higher than anything we have outside or even inside the house. Outside humidity today, for example, is about 20% and it is 93 degrees.

The big question I have now, though, is whether the glass, which is really opaque 6mm twin-wall polycarbonate, provides what is considered filtered light. Do I need an extra layer of sunshade or anything to protect the orchids from direct sun, or does the polycarbonate already do that?

I get readings of between 25k-50k lux in the area where the tomatoes are growing now, with the somewhat milder October sun. That seems like it would be the range for my Cattleyas, but I'm afraid of cremating them! Arizona sun is pretty brutal.

Advice?

[ollypolly]

First of all YUCK! to your whether. Where I am in Oz it's 28deg C (82F) and about 50% humidity (Still too dry for my tastes). I say yes you need some shade cloth, maybe not so much coming into winter but when spring arrives you probably will need it . That's just my opinion from living somewhere with really intense sunlight. Also do you have good ventilation and air flow through your greenhouse? Stagnant air breeds disease.

[Raqsharqi]

The greenhouse is 8x8....just a hobby greenhouse. It has two vents on top that open automatically when it warms up. There are two side louvers as well, and a fan to get whatever moisture we have circulating.
Normally, when gardening outdoors, I don't need shadecloth this time of year. I MUST use it once temps are over 100 or the tomatoes crisp up. I had hoped the same rules might apply to the greenhouse. If I use the aluminum cloth the manufacturer sold us, the light (lux) drops quite a lot. I could try to drape something on the inside, though that can also trap the heat inside the greenhouse.
Normally at this time of year we should be about 83 degrees. We're running a good 10 degrees above normal. On the bright side, this gives us a little practice dealing with what the summer will bring.

[ollypolly]

Sounds like no air flow problems then. Hmm... maybe leave the orchids as they are but keep an eye out for red leaves (a sign of sunburn). Maybe get some tiered shelving and put the light hungry orchids on top and the lesser ones on the lower shelves using the orchids themselves to create the right light conditions.

[katrina]

Most orchids aren't going to appreciate the same level of sun intensity that tomatoes love and thrive under. The term crispy critters comes to mind.

What cattleyas are you growing? Some will burn up in more than 2000 fcs and others, like the rupiculous types, can take full on direct sun.

[Raqsharqi]

I have the kind of eclectic collection only a newbie would assemble. I picked orchids I liked that sounded relatively easy! I have three cat types: Aristocrat glauca, Picotee Passion, and my rescue plant...Achung Ruby. The Picotee has been with me the longest and is in sheath. I think it looks great in the shady area of our little courtyard...the leaves are apple green. The Ruby is a very new addition, so I don't really know how it's doing yet other than it seems okay. I attempted a "little direct morning sun" with an Oncidium and badly sun scalded the leaves, so I'm afraid of trying sun exposure to anything but maybe the Ruby as I'm not so emotionally invested in it!

All my orchids are growing more or less happily against a shaded wall in my courtyard where they get perhaps the minimum lux required for a phalaenopsis. It's hard to gauge exactly because there are 4 sides to the courtyard and the sun no longer passes directly overhead. I would only get direct exposure if I put the orchids against the north wall where light would reach as the sun moves in a slightly southwestern trajectory. Fortunately, my orchids haven't been reading any manuals and don't know that they shouldn't be able to grow in our hot, dry desert environment. I'm sure the fact that I put them outside during the rainy season helped some, but the fact that they adapted to our hostile environment gives me hope!