Greenhouse positioning

Question

When building a greenhouse, we can all reckon that it should get as much light as possible (with proper heat ventilation).

BUT, let's talk about when a greenhouse must be built near shade. Consider a south-facing 8'Wx6'Lx6.5'H greenhouse that must be positioned to get shade either in the morning or evening (from east or west), due to 8' structures/trees on each side. It cannot be positioned in the middle with equal shading morning vs night.
Which is more important: morning or evening sun?

Mostly vegetables will be grown. Tomatoes, peppers, beans, squash, etc.

Yes; similar questions have been asked here, but I'm specifically referring to greenhouses because they hold heat and have other different variables.

My presumption is that evening outside air will already be warmer, so getting evening sun might be "less useful" than morning sun because the greenhouse will have lots of stored heat later in the day. Thus I'm guessing that it would be best to have the greenhouse more toward the west, so as to soak up more morning sun and sacrifice evening sun.

Answer 1

In my opinion you should determine which position has the longest photo period throughout the year. The variations between the morning and evening positions are affected by the shape, location and size of the surrounding shade-producers, height of the sun, etc. You may decide you like morning sun better and find that the morning sun position is completely shaded for 3 months in winter.

I don't think morning or evening makes a lot of difference for your plants from just a time of day standpoint.

Looking at the situation mid-summer won't give you an accurate picture of what fall/winter/spring will look like. If you are going to grow all year, the winter photo period may be more important or there may be more variance between the photo periods in winter.

In my situation, I grow cactus in AZ, so if I had to pick I'd take morning sun. The plants and air are cooler in the morning and less likely to sunburn. But, I am in a pretty extreme environment, so YMMV. If I had the option for full sun all day I'd take that and attenuate the light levels with shade cloth.

Bottom line, figure out which position provides the most sun during the times of the year that are most important to you.

Good luck!