East Window versus West Window

[Mountaineer370]

This is something that has been bothering me for a long time, and I have not found a satisfactory answer in any of my online searches. I hear all the time, on this board and from many other sources, that for the most part, an east-facing window is fine for most orchids, but beware of a west-facing window, as it may be too hot, the plants could get burned, etc.

This topic came up again in conversation with someone at an orchid show I attended yesterday, and that's what made me decide I was going to try to find the scientifically valid reason for the west-window warnings.

When the sun rises in the east and sets in the west, it is, for all intents and purposes, the same distance from our planet for the whole day. The temperature of the sun does not change from morning to evening. How can the sun coming through a west window possibly be "hotter" than that coming through an east window?

Yes, of course I know that the outdoor temperature generally gets warmer as the day goes on, but I'm talking about indoor growing here, and for most of us, that means a temperature-controlled interior environment.

I can see where differences may arise depending on the size of your respective windows, whether there are any porches or awnings, and whether the window is shaded by trees or structures. That could definitely make a difference. But I am having a hard time understanding the often-given reason that sun coming in a west window is hotter or somehow "stronger" than sun coming in an east window.

[Orchid Whisperer]

Depending on the situation, either an east or west window could be fine. But, the light is not the same.

In the morning, the east/morning sun is more likely to be cutting through more haze/fog/humidity than in the west/evening. Hence dew in the morning. That cuts down light intensity.

That lower morning temperature may be a factor too. Though I think it is more important for plants grown outdoors.

[Laticauda]

You can try an experiment.
Get a cold cup of milk and a heated cup of milk. Now add hot water to both and taste them. The milk is our atmosphere and the hot water is the sunshine.

[camille1585]

Sometimes information is repeated through the years because it's been said in the past and passed down, and the context has been lost.

But I suspect it has at least something to do with the fact that even indoors, it's usually warmer at the end of the day and combined with the light, sensitive plants can overheat or burn. Back when I had a few masdevallias I grew them in an east facing window because that room generally stayed cooler than the room that faced west.

I don't like these general sweeping comments because it depends too much on the type of orchid and also how far north or south you are located. I've grown many orchids in both east and west facing windows without seeing much of a difference, except for a few specific genera. And I'm so far north now that I grow everything (including Phals) in south facing windows.

[CJ Green]

I don't have any scientific answer, but anecdotally, I've found that maxim to be true. The afternoon sun coming through my west-facing windows is intense and lasts longer than the morning sun. And unless your windows are super-great at insulating (mine aren't) I think the temperature is a factor, especially if your plants are very close to the window itself. If you want, you could set a thermometer on your windowsill and record the temperature--I have an inexpensive thermometer/hygrometer that records the high/low for a 24-hour period. It's interesting to note the fluctuations.

[Mountaineer370]

Thanks to all of you who replied. The humidity often being heavier in the mornings is something I had overlooked. I'm sure tiny water droplets suspended in the air would reflect sunshine back, making what reaches the windows less intense. (I'm thinking the extreme example would be fog.)

I agree that everybody's house can be different. I'm sure that the type of windows you have makes a difference. Also, the distance from the window that you place the plants.

It was just one of those things that you hear repeated often, and there comes a time when you think to yourself, "Why does everybody say that?"

[Laticauda]

Cheri, it's better to question conventional wisdom, ask salt and fat!

[Ray]

The hydroxyl radicals within water (the O-H bonds) have a resonant frequency that is a close match to part of the infrared spectrum, which might attenuate some of the morning heat.

I learned that when working with Bell Labs in the early development of optical fiber waveguides, and it never occurred to me how that might apply to sunlight.

[malteseproverb]

I too have anecdotal evidence! I used to grow all of my orchids in west windows for several years, and 2 years ago I switched to east windows after a move. Every single one of my plants has improved in the east window set up. In the west windows, many plants suffered and struggled to put out good growth despite getting PLENTY of light, and I believe this was all due to temperature. You talk about climate controlled, and maybe that is true for you, but I don't run my AC when I'm at work. By 5pm those west-facing rooms are already sweltering in Philadelphia summers.

The way I see it, as a windowsill grower, you want to get as much of that summer sun as possible. If you grow in an east window, you can maximize your direct sunlight and keep plants closer to the window without worry.

[Mountaineer370]

I suspect it wouldn't make any difference in my house. A few years ago, we had all new well-insulated double-pane windows put in. We also have quite a few trees on both the east and west sides of our house. One of us is almost always home all day, so the AC stays on in the summer and the heat in the winter. The indoor temps don't vary much at all.

I think each of us has to look at the layout and construction of our own home, our own lifestyle, any outdoor landscaping or structures, etc., and make our own best judgment call as to where the orchids will be happiest. I only wish I had some available space by the windows on the east or west where I could try it out!