Confused about light requirements - max vs average etc - Orchid Board

Benno · #1 10-20-2018, 05:08 AM

I'm trying to make sure my recently growing orchid collection is getting the correct amount of light. I have one several year old mini phal that has dark green leaves as it was inside on an East facing window ledge but with a patio outside, in a position that was definitely too dark - yet it still bloomed! The rest of my phals are newish. I've moved that first phal to the brighter patio but have started adding to our collection of Orchids!

Anyway my question is around the general requirement that phals not get more than 1000-1500fc. Does that have to be sustained most of the day? Or is it that it should peak daily in this range but most of the time be lower than this (like a bell curve)? My only easily suitable place is an east facing patio. The roof is about 3-4 meters high and it's about 7x4.5 meters in size with the house blocking off most of the north and west faces. (I'm in Aus so north for us is like northern hemisphere south when it comes to the sun's angle). I can place orchids so they never get full sun on the patio.

Using a phone light meter (which I somewhat calibrated using a DSLR camera) I can place orchids on the patio to receive a peak of 1500 ish fc in the mid morning due to lots of light bouncing off the patio tiles and white patio ceiling, but much of the day is much lower. Eg this afternoon at 2-3pm it was about 300fc. It was a cloudless.day.

I found that even standing outside in the shade from a small tree, with an open sky above at 3pm only gave about 500fc anyway! The only way to get more light seems to be to go in the full sun and use shade cloth, but to limit this to 1500fc at midday means it will be getting much less light in other parts of the day anyway...

Thanks for your help in advance!

Ray · #2 10-20-2018, 08:13 AM

First let me say that phalaenopsis tend to be "deep shade" plants in the first place, and that plants can adjust to changes in light levels. I will add that the best grown phals I've ever seen were in an algae-covered greenhouse that was so dark, it took my eyes a couple of minutes to adjust when entering.

The light level recommendations published tend to be "peak" levels that they plants might be exposed to a noon.

If you look at the progression of light from zero at dawn to the peak at noon to zero at dusk, it resembles a triangle. The area inside that triangle represents the "volume" of light the plant is absorbing, and the area is calculated as 1/2 base (hours dawn to dusk) x height (max intensity). Therefore - and this is most useful for folks growing under 100% artificial light - the average intensity is about 1/2 of the maximum recommendation.

estación seca · #3 10-21-2018, 01:48 AM

Phals grow and bloom fine with no direct sun ever hitting their leaves. This can be so little light there is no shadow cast whatsoever - one definition of full shade. I have been told by a commercial grower that they flower better in lower light rather than higher light.

Benno · #4 10-21-2018, 02:13 AM

Thanks for your feedback. I think you're right they should be ok there. Most of the morning they get >500 fc. After posting I also eventually found Ray had further information here: Light Level Recommendations >> First Rays LLC

But I've just added my first 3 Cattleyas to the collection

Went to a show today (first time I've been to one) and it was fascinating.

Edit: For any sciencey people, look up the "DLI" (daily light integral, measured in mol∙m-2∙d-1).

estación seca · #5 10-21-2018, 03:24 AM

This isn't science class, but you mean moles (of photons) per square meter per day, and the caret is needed to indicate an exponential: mol • m^-2 • d^-1

Benno · #6 10-21-2018, 03:29 AM

Quote:

Originally Posted by estación seca

This isn't science class, but you mean moles (of photons) per square meter per day, and the caret is needed to indicate an exponential: mol • m^-2 • d^-1

Sure do, sorry its just the way I pasted it in

cythaenopsis · #7 10-30-2018, 12:15 PM

Quote:

Originally Posted by estación seca

Phals grow and bloom fine with no direct sun ever hitting their leaves. This can be so little light there is no shadow cast whatsoever - one definition of full shade. I have been told by a commercial grower that they flower better in lower light rather than higher light.

Thanks! This is good to know.

I have a mini-Phal that is now 3 years old, and is growing a new shoot for its 5th bloom (it usually blooms twice a year and skipped once). I've kept this on an East facing window, so it gets a couple hours of direct sunlight, then ambient light for the rest of the day. It had a stunning bloom earlier this year -- two stalks and 18 flowers overall. Over the course of the leaf growing season, the leaves grew enormously (compared to previous years) so I'm hoping it'll do well this winter.

On a side note, I inherited a very large phal, two plants in one pot. After the blooms fell off, it is growing new leaves despite each plant having 4 very large healthy leaves. But the stems aren't "retreating" as I've experienced on my mini-phal. Meaning, the plant sucking back nutrients and causing the stem to shrivel and die. At this point, should I cut back the stems, even though they're still healthy?

aliceinwl · #8 10-31-2018, 01:52 AM

Cutting of green stems is your call. I've left them on some plants and they produced a really unimpressive flowering display from the old stems. On other plants, blooms from the old stems were just as, if not more, spectacular than the originals.

I don't do partial cuts to try to force a second bloom: I just let nature take its course or cut above the first node to do a complete removal.

cythaenopsis · #9 11-01-2018, 12:28 PM

Quote:

Originally Posted by aliceinwl

Cutting of green stems is your call. I've left them on some plants and they produced a really unimpressive flowering display from the old stems. On other plants, blooms from the old stems were just as, if not more, spectacular than the originals.

I don't do partial cuts to try to force a second bloom: I just let nature take its course or cut above the first node to do a complete removal.

Thank you, Alice. I think in this case, I'll let nature take its course. It has been a month now since the phal ejected all of its blooms and the stems are holding up well. They're so nicely formed with ample support... just thought it would be a shame to snip them off. In the past, all of my phals have usually sucked the nutrients out of the old stems, so I didn't have to think about this.