photoperiod in orchids, PLEASE COMMENT

[professor plant]

I recently read an article that said that most orchids do not require a specific photoperiod to grow or bloom. It was suggested that most orchids can grow and bloom under lights that run 24 hours a day. I am interested to know...
Does anyone know which do and which do not?

What is the difference in these plants scientifically?

How can one tell the difference?

Does anyone actually grow and bloom orchids under 24 hours of light?

[Connie Star]

My understanding is that most of the orchids we enthusiasts grow are from the tropics, which means there's very little change in day length thru the year. I grow most of my 'chids (about 80, various genera) in a south facing window wall in the Northeast. I have some under lights, and I set timers for 11 hours during the winter and ramp up to 16 around the solstice. I also put most of them outside, under shade cloth during the summer. Of course since they are in living space the room lights are on/off at various times, too.
I think they do need time in the dark and I don't think you can "force" them by leaving lights on 24/7.
Where do you live? I'm in western Massachusetts.

[orchidsarefun]

why you would want to grow orchids under 24/7 lighting ? More growth, more flowers ?
I think that many hybrids may withstand conditions that are not close to the natural conditions of the species but there is a reason why many orchids flower in summer ( higher temps ) or in fall/winter ( diurnal impact ). Obviously commercial growers "trick" orchids to flower all year round, but having rescued orchids from big box retailers I have noticed that there is a definite extended acclimatisation ( sp ?) period for these to get back to "normal" growth and flowering.

[Call_Me_Bob]

dont plants have stomata that close at night to conserve water? or something like that.

i would think its best to replicate nature

i have my lights on 13 hours about and once it gets warm enough they go outside

[BruceP]

Originally Posted by professor plant

I recently read an article that said that most orchids do not require a specific photoperiod to grow or bloom. It was suggested that most orchids can grow and bloom under lights that run 24 hours a day. I am interested to know...
Does anyone know which do and which do not?

This topic was discussed in a previous thread:
24 hour photo period?
I don't think that I could do any better than Undergrounder in summarizing the basic science behind it. Note that it is not just the day length, but also light intensity, temperature, quantity and types of water nutrients available, and CO2 concentration that must be considered.

Originally Posted by professor plant

What is the difference in these plants scientifically?

The difference is in the type of photosynthesis employed by the plant (C3, C4, CAM). Most orchids will be either C3 or CAM - terrestrial and thin-leafed epiphytic varieties will generally be C3 and the thicker-leaved types CAM.

[Vanda lover]

I remember reading that outside lights such as street lights can prevent blooming. I don't know why someone would use the extra hydro when plants bloom fine without it. I know that I prefer darkness for sleeping and I assume my plants do too. It's only natural.

[professor plant]

I agree with much that has been said. I know from my growing experience that orchids fair better when 'comfortable'. To have lights running all day or for a large proportion of it, would be stressful. I am now growing in a terrarium setup and have had great results with the light running at 14 to 11 hours, with more light in the summer.

I have just been trying to think outside the box. I know other non-orchid growers who have a great amount of success running long periods of daylight, but to induce flowering, that has to be lowered. To increase my seedlings growth rate can I apply the same principle?

So again, my question is, what determines a plant to have a photoperiod? How is this established by the plant itself in its makeup? And what is the difference between a plant that has this, and one that does not?

Thanks
Chad

[BruceP]

Originally Posted by professor plant

So again, my question is, what determines a plant to have a photoperiod? How is this established by the plant itself in its makeup? And what is the difference between a plant that has this, and one that does not?

This is a complicated and not well understood issue having to do with the creation of, and the interaction between, the various plant hormones that regulate the initiation of the reproductive processes. It is somewhat analogous to asking why two species of goat - one from a temperate region and one from a tropical region, say - go into estrus at different times of the year. The "difference" you're looking for is going to be found deep in its DNA resulting from long-term evolutionary adaptations to improve overall reproductive success within prevailing environmental conditions. One can use exactly the same hormone treatment to induce estrus artificially in either species. The 'why?' is much better understood than the 'how?' in both plants and animals.
A couple of basic takeaways:
Photoperiodism does seem to be genetically fixed at the species level and is carried forward in predictable ways in hybrids.
The dark period is more important than the light period in initiating flower development. Both long and short day plants will flower with equal periods of light and darkness.
The 'dark process' can be easily be disrupted by even short periods of light.
Other factors, such as temperature, also play a role in these processes.

Here is a fairly concise and easy-to-understand discussion of photoperiodism.

Originally Posted by professor plant

I have just been trying to think outside the box. I know other non-orchid growers who have a great amount of success running long periods of daylight, but to induce flowering, that has to be lowered. To increase my seedlings growth rate can I apply the same principle?

In a word, yes (with some qualifications). In this case, you're working with the much better understood processes associated with photosynthesis and vegetative growth. Be aware that your "non-orchid grower" friends may be working with a homogeneous crop rather than something like a mixed collection of orchids and can 'fine-tune' all of the the cultural elements related to that specific crop.

[Discus]

Has anyone come across a fairly comprehensive list of what orchids are day-length sensitive? I'm starting to think the super-bright street lights just outside my growing area might be putting some of my plants off

[Connie Star]

Quoting:
Here is a fairly concise and easy-to-understand discussion of photoperiodism.

Interesting article.