It is finally warming up in Humboldt County, after an extremely cold spring with snow flurries in April -- very unusual for us. My greenhouses are not heated in winter, and other than fans, there is no cooling system. One of the problems with our foggy climate is that temperatures in the greenhouses can swing more than 50 degrees F. in 24 hours, heating up on the sunny days, and cooling at night. This is a bit extreme, even for bulbs. Most of the bulbs I grow come from climates where the temperatures reach 100F at least, but growing them in black plastic pots is another thing entirely, since the soil temperature in a pot can get much higher than the soil temperature would be in their natural environment. In the wild, bulbs often grow at great depth, escaping the scorching temperatures on the surface. In a greenhouse, we have to take some steps to moderate the temperature.
I recently installed a product called Aluminet, a knitted aluminum coated shade fabric. Shading in a greenhouse is more effective if you can put the shade fabric on the outside of the structure, but in this windy climate this is impossible. Aluminet is more expensive than traditional shade fabric, but it has other attributes that make it worth the expense. It is feather light, and can be suspended by clips from the frame of the greenhouse. Because is is metallic and shiny, it reflects the light. I bought 40% shade fabric, and was worried about it reducing the light intensity, especially on our frequent foggy days. It doesn't seem to do that at all, in spite of the 40% rating. Another bonus is that the fabric itself doesn't heat up, unlike black plastic shade cloth, and you can place it directly on top of the pots, as I have done, on some seedling pots that are going dormant. The bulbs, at this stage, are tiny and are in the top one or two inches of potting mix, so they can desiccate if they get too hot. In their natural environment they would probably be shielded by drying grasses or adjacent vegetation.
The temperature reduction so far is about 15F on sunny days. I have not shielded the side walls, and intend to do that to reduce the temperature more.