Greenhouse blues

[Raqsharqi]

I have an 8'x8' greenhouse with 6mm twin-wall polycarbonate panels. It sits with the doors facing east. I have tomato plants at the west wall, the cooler and a plant stand/work cart with dendrobiums and some catt type orchids on top. In the southeast corner I have oncidiums, mostly, and a miltonia. There are other vegetable plants along the bottom of the south wall. I have my phals in the shade of the other vegetable plants. I put double shadecloth on the eastern half (the shade runs north to south) to protect the orchids. There is a little shade cloth hanging down about halfway on the south wall, because when the sun tracked lower, the light was too intense on that wall. And that was mostly okay until now.

I now have some sunburn on an oncidium and the cochleanthes (which was with the dendrobiums) has a crispy leaf. If I put that aluminum type shade cloth on top of the entire greenhouse, the light levels drop way too much, IMHO. When I take the light meter out there, the phals mostly get the right amount of light until midday, and then it is too bright/hot. The oncidiums, which have been growing well, but not flowering, are really in too little light now, according to the meter. But since I've had leaf burn there, I'm afraid of giving them more light. I have a dendrobium superbum and a maxilaria tennefolia hanging in a spot without a sun screen, and they seem content, as does the baby vanda.

What should I do for the summer? If I cover the whole thing, the high light plants don't get enough. In fact, the phals are about the only ones that are in the sweet spot. The oncidiums would be in even less light than they are in now.

8x8 is really too small for me to have comfortable zones, and since the greenhouse was originally meant for the tomatoes, I can't sacrifice them. Normally, I'd go out there every afternoon and move the phals around a little, but we'll be on a long vacation and no one will be around to do that. Yes, someone will water twice a week, the cooler is on a temperature timer, and we have an automatic mister, but light...ah, that's a problem. And heat, as we have already hit 95 in there, though Andy of Andy's orchids assures me that the orchids can handle the heat if I can give them some humidity...kind of a tricky thing here in Arizona.

Help? Anyone?