Light Requirements Amongst Cattleya Alliance

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People have successfully flowered Cattleyas under almost every kind of electric light invented. I think most people at this point starting from scratch would go with LEDs, and not older technology that uses more electricity for less light output.

[SouthPark]

Originally Posted by Subrosa

In PA I keep aclandiae, dowiana, and trianae in as much sun as I can give them.

I confirm that aclandiae and dowiana can handle quite a lot of sun. Once sun-hardened, aclandiae and dowiana and lots of other catts can take quite a lot of direct sunlight for sure. I have some nice natural air-movement in my growing area - that probably helps a little bit. But not sure how much.

[Steve83]

Pdxtyler, do you mean you're thinking of using an 8 bulb t5, or 8 bulb t5-led conversion?

t5 led conversions will fool you because they don't generate as much heat, but they are more powerful than the t5 tubes, and an 8 bulb t5 conversion covers a 4x8 canopy from a distance of about 2ft., maybe a bit more.

This experience is based upon indoor hydroponic and organic gardening. But light is light. If you're looking to flower, photoperiod is usually the first thing to research, then intensity.

Be prepared for opening pandora's box though. Increased intensity creates a need for more food, and water (humidity). If you have a local hydro shop, pay them a visit and tell them exactly what you're trying to accomplish.

I myself just purchased a small evap humidifier to keep humidity bumped up in my ceramic metal halide tent. Muffin fans are next... lol

[Fairorchids]

While a few species prefer less, most Cattleyas can handle more light than you expect.

For years I have grown my Laelia anceps in full sun here in NJ. If weather patterns allow, I bring them outside in late April (I have to be prepared to bring them back in if we get a late frost), ideally on the first of a 2-3 overcast days forecast. If I bring them out later, then I have to harden them in light shade for a few days. They stay outside till at least early Oct.

If there is no rain, then I water 3 times a week, and fertilize every 2 weeks.

Several years ago, I also grabbed a couple of Lc (both half anceps) by mistake. Not only did they do just fine, they both grew and flowered much better than they did when summering inside the greenhouse.

This photo shows Lc. Miss Wonderful 'Imperialis' after that first season outdoors. You can see the 'floppy' older growths, and the strong growth produced outdoors in full sun.

Based on this, and other experiences, it was my intention to experiment with C. (L.) purpurata the next season. Unfortunately, all the purps were victims of the freeze in the greenhouse, so I have been unable to test this species. However, I have a bunch of purpurata and tenebrosa seedlings coming along, so I will experiment further in the next couple of years.

[thefish1337]

I get that you "can" put your Cattleya in more light however I'm hard pressed to believe that excess sun is beneficial. From a plant physiology perspective its unlikely that your orchid can utilize full sun or excess light and put it to use. Cattleya do well with a daily light integral of 12-16 maybe a bit higher if you want to "push" them. Full sun produces 900-2000 μMol/m2/s and if we generate DLI values from a low end estimate of about ~1000 PAR you will find that in 4 hours the orchid has all the light they really need. If we look at that on the high end (blistering hot full sun) it would take half the time to receive enough photons needed by the plant. Furthermore because most cattleya utilize CAM photosynthetic pathways, utilization of light is limited by how much CO2 your orchid can fix during the night. Another caveat is that if leaf temperature starts to exceed 95 degrees plants will begin to shut down their photosystems and stop photosynthesis all together, I'm sure there are exceptions but most of the time super high light is accompanied by lots of radiant heat. Many people mistake "this plant can survive in these conditions" with "this plant is enjoying these conditions". It's far more likely, in my opinion, that reports of Cattleya doing better outside in the summer under high light conditions is more due to improvements in the environment that allow for more carbon to be fixed at night. Keep in mind daily light integral is assuming that photosynthesis can occur at the given light intensity and I've outlined multiple reasons why photosynthesis might not be occurring in full sun situations.

[SouthPark]

fishy ------ it is true that 'excess' sun can/will indeed destroy an orchid. A blazing sun and hot day - and a leaf not able to cool down ------ overheat in portions or whole leaf --- can certainly destroy the orchid. Leaf, bulbs and all.

During the year - in some or many places, the yearly maximum sun light intensity can scorch the living (and not-living) daylights out of many orchids.

So while catts are sun-hardened, the long-time growers know (or likely know already) roughly what conditions those particular orchids can handle (as in keep surviving and growing and flowering - year after year).

We know that many orchids that grow in full sun get burned in the wild too ..... leaf scorch. They can generally tolerate some leaves getting scorched.

For home-growers, just being aware of what peak yearly sun intensity can do, and being aware roughly what the orchids can handle is certainly beneficial. For orchids that obviously have/get issues in full sun after substantial sun-hardening periods of time ----- we just better move those ones to different spots.

[thefish1337]

Originally Posted by SouthPark

fishy ------ it is true that 'excess' sun can/will indeed destroy an orchid. A blazing sun and hot day - and a leaf not able to cool down ------ overheat in portions or whole leaf --- can certainly destroy the orchid. Leaf, bulbs and all.

During the year - in some or many places, the yearly maximum sun light intensity can scorch the living (and not-living) daylights out of many orchids.

So while catts are sun-hardened, the long-time growers know (or likely know already) roughly what conditions those particular orchids can handle (as in keep surviving and growing and flowering - year after year).

We know that many orchids that grow in full sun get burned in the wild too ..... leaf scorch. They can generally tolerate some leaves getting scorched.

For home-growers, just being aware of what peak yearly sun intensity can do, and being aware roughly what the orchids can handle is certainly beneficial. For orchids that obviously have/get issues in full sun after substantial sun-hardening periods of time ----- we just better move those ones to different spots.

I'm just challenging the suggestion to give your cattleya as much light as they can take just because they can "take" a lot. They can tolerate a lot more light than they actually can use. Doesn't mean that sun is actually doing anything for you for the reasons I stated above.

You can use a cell phone Lux app to easily calculate/estimate PAR from sunlight. You can measure it throughout the day and estimate DLI. If you know your DLI you can decide to increase it or decrease it depending on how your plant is responding. It's unfortunate that in 2020 we're using subjective terms and archaic measures like footcandles (nearly every AOS guide) to assist people with orchid culture. Even worse, playing guess and check with your precious orchids in the sun.

These measures are not scientifically perfect but they should be reproducible and reliable and get you close enough. I would shoot for a DLI of 15 for most Cattleya and adjust up or down from there. Your cell phone and a bit of simple math and you're golden.

Measure Lux
Lux Meter for Your Phone

Calculate PPFD from Lux




Estimates for artificial lights

DLI from PPFD

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Different phone CCD chips (charge capture device, the camera chip) have different parameters. Unless the software was written for the specific CCD in a specific phone it will not be accurate.

[SouthPark]

Originally Posted by thefish1337

I'm just challenging the suggestion to give your cattleya as much light as they can take just because they can "take" a lot. They can tolerate a lot more light than they actually can use. Doesn't mean that sun is actually doing anything for you for the reasons I stated above.

There will be uncertainty in the light levels (intensity) for outdoors. We know there are going to be catts that won't handle peak intensities, or intensities above some rough level - regardless of sun hardening. Not just peak intensity - but exposure to those intensities for some amount of time. This is considering environment temperature and other conditions too.

I don't grow my orchids under really well controlled lighting conditions. The main inputs I put in - has been observing the daily and yearly conditions (through-out the year) and sun-hardening - and deciding on where to put particular orchids, so that they don't get scorched. Or if they do, then not scorched badly. And the other input is just watering the orchids (and fertiliser, and mag-cal).

As much light as they can handle will still require the important aspects ----- like still grow well, flower well, and survive - year in and year out ..... indefinitely.

I agree ------ using sensors and logging devices can definitely help us look at the conditions in a convenient and effective way. That will go nicely towards determining nice spots for orchids to be placed - outdoor or semi-outdoor ones that is. I think I will get around to doing some measurements using various sensors for summer seasons - out of interest! It will be nice info to have.

I like the idea of using sensors to provide a better picture of the lighting levels/intensity. This, combined with temperature and other data could be very handy.

[SouthPark]

Originally Posted by thefish1337

I get that you "can" put your Cattleya in more light however I'm hard pressed to believe that excess sun is beneficial.

That is true. Systems have some region (aka sweet spot region) where something like growing is best - or optimum. There will be considerations like light level, and temperature, and nutrients, elements input, etc.

For the regular home grower, just putting the orchids in a spot where the conditions stay satisfactory is a good start. Doing extra - like optimising or tweaking things can come later - as options only.