Purple tinge on new growths.

[MateoinLosAngeles]

I always understood that purple tinge or spotting on new Cattleya growths indicated the plant was getting enough light. Perhaps "up there," but not enough for the plant to burn, sulk, desiccate, and all that not-good stuff.

My Catts get A LOT of light and receive direct sunlight for about two to three hours daily in Summer. As a result, some have purple spotting on new growths, some don't, they all look pretty "light" green, and I have many of them growing thick fat roots like crazy.

However, I was reading an article (I WISH I could find it!) that suggested the purple spotting indicated the plant was receiving too much light, not "up there," but more than it can process. Thus blocking the effective distribution of calcium in the tissue, which causes purple spotting.

I have heard everything regarding plant coloration and nutritional deficiencies. Everything except for definitive evidence or effective ways to know that the coloration isn't caused by something else. So I'm having a hard time assuming this Calcium thing isn't a myth (or if accurate, relevant to the growth) since so many growers have purple-spotted cattleyas and grow them without issue.

What do y'all think?

[estación seca]

Some Catts make purple spots and some don't. In some it's related to light and in others it isn't.

You might have read this in some notes I took in a talk by Alan Koch:
Alan Koch: Cattleyas 365, 24/7 June 18 2020 - Orchid Board - Most Complete Orchid Forum on the web !

He said Cattleya aclandiae flowers best in lower light than is preferred by other bifoliates. He suggested reducing the light until they stop making spots on vegetative parts. He also mentioned other Cattleya species that flower better in much lower light. He said the effort the plant spends making the anthocyanins diverts energy from flowering.

This information is mentioned in another thread devoted to growing under lights: Light Requirements Amongst Cattleya Alliance - Orchid Board - Most Complete Orchid Forum on the web !

Over the last few years I've seen many instances of people pushing light levels very high for many different kinds of plants. This wasn't as possible before LEDs because such light levels led to very excessive heat levels. Too much light is harmful to plants even in the absence of heat. Chlorophyll is eventually degraded by light exposure and the plant needs to synthesize more. That takes energy away from producing vegetative growth and flowers. The process of converting photons to energy always produces some free radicals that can be damaging to cellular organelles. Plants have mechanisms for dealing with this, but when getting far more light than they ever would in their native situations they may become overwhelmed, and tissue damage may occur.

The right amount of light is the best. Too much doesn't help.

[Dimples]

I give my phals very high light during much of the year compared to what is suggested in the literature. It’s a situational compromise because I don’t have anywhere else in the house for them, and my other houseplants would suffer if I further reduced the incoming light.

Summer has the lowest light intensity with the longest duration and most closely matches phal cultivation guidelines. Mid-fall and mid-spring are the highest direct intensity with moderate day length. Sheer curtains diffuse the light all year, but it’s a southern exposure. The phals in my collection that can produce purple coloration do (not to excess) but I’m aware that the purple pigment indicates the plants are beginning to protect themselves from the possibility of cellular damage.

My phals that don’t have the ability to produce purple coloration don’t show any obvious signs of stress (not overly pale, no burns, growth is normal, etc.) so my anecdotal assumption is that the anthocyanins can be preemptive and don’t necessarily indicate damage is occurring, but ideal growth likely happens right below the threshold where purple starts showing up on the plants that can produce it.

I think the purple tinge is pretty, my plants are happy, so I’m not going to change anything until (if) we buy a house.

[isurus79]

My goal is to get purple on the leaves. If its a plant that has the ability to turn purple and there's no color change, I consider the light insufficient for the plant.

[Louis_W]

Originally Posted by isurus79

My goal is to get purple on the leaves. If its a plant that has the ability to turn purple and there's no color change, I consider the light insufficient for the plant.

I feel exacrly the same!

Mateo, one thing to remember is that very dark colored flowers generally correlate to darker pigments in the leaves so dont try to push albas or coeruleas to turn purple, because they dont have thos pigments. They would probably fry because they cant make their sunscreen

Ps i grow catts so im not sure how well this works for other genera.

[SG in CR]

Not directly Catt specific, but, there are a few species fo orchid in my area that I've seen growing in everything from full sun to fairly deep shade. Notably Trichcentrum ascendens, Trichocentrum crispiflora and various Encyclias. The biggest healthiest plants are never the ones fully exposed to mid-day sun. The Trichocentrums get almost entirely purple foliage and all three of them never reach the size that they do when they are in a spot that gets plenty of light but not fully exposed to the noon sun. Though full sun plants tend to bloom pretty well even when the plant seems stressed. When they don't get enough light they get long narrow leaves and bloom far less.
The exceptions that I know prefer full sun are species like Catasetum maculatum and Myrmecophila tibicinis, but they don't purple up in the sun and really suffer in the shade. I have a Catt. maxima that I've been keeping in the full sun because I was told that's what they prefer, but the plant sort of reminds me of the sun stresses orchids. I think I'm gonna put it under shade cloth next dry season.
My 2¢, Orchids that can tolerate full sun but get purple in response probably do best when they have enough light to just barely have some purple tinge to the foliage, but beyond that they would probably do better with less light.

[Roberta]

Just a note when increasing the light on a cultivated plant... do it gradually, over several weeks so that it can acclimate. Just like it's unwise (and rather painful) for a light-skinned person who has been indoors all winter to hit the beach on vacation without lots of sunscreen. (You can tell who made that mistake by noting who resembles a boiled lobster) Plants are similar - after gradually increasing the light until it's quite bright, the plants are fine. Do it suddenly and they toast. Spring is a good time to do that (like now in the northern hemisphere), get them ready for summer.

[smweaver]

Originally Posted by isurus79

My goal is to get purple on the leaves. If its a plant that has the ability to turn purple and there's no color change, I consider the light insufficient for the plant.

Same here. And some cattleyas--especially amethystoglossa and bicolor, in my experience--get lots of purple spots and blotches all over their new leaves without showing any sign of burning (the spots eventually fade once the plants come back indoors in the late fall). I think the spots are just the new growths' version of suntan lotion.