Photoperiod - what is the appropriate 'winter'?
 

Growing under lights, it is feasible to control intensity and duration (and, of course, temperature and humidity, as well as nutrient supplies). One can reduce winter (cooler, dryer, shorter days) to the minimum needed to initiate bud formation or dormancy requirements for those orchids with seasonal cycles. AOS publications suggest a 'several month' duration of shorter photoperiod for mixed collections or sensitive plants. My question is: what is the minimum time for this winter break? I'd rather see my plants growing fast, rather than idling in the cold and dark. Has anyone reduced winter to one month with success (for photoperiod sensitive orchids)?

There is no single correct answer. It depends a lot on what you are growing. What genera do you have now? Intend to acquire soon?

I am growing Cattleya, Phalaenopsis, Paphiopedalum, Phragmites, Dendrobium - and some others. As with most of us, it is a mixed collection.
I read that a period of reduced temperature may substitute for shorter photoperiod in initiating bud formation, but I have the same question about this - how short a cool period would do the job?

A general rule of thumb is to follow the seasons, so time the lights to seasonal lighting. My windowsill orchids don't get supplemental lighting and do well. I think that my under lights orchids roughly get about an hour more than those on the racks at the windows.

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But - since we can play 'Master of the World' in the totally artificial environment of a grow room, I'd like to supply conditions for maximizing growth without inhibiting flowering. Growing epiphytic orchids on a Chicago windowsill is artificial, you're just letting the sun (at that latitude) call the shots.

Look at the latitude where the specific orchid in question is found. The photo period each day of the year is easy to determine for a given latitude.

I think if you are looking for a general answer I would try about a two months period. I only gauge that by how long a Den nobile type orchid needs to rest before bud initiation


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Not so easy for multi-generic hybrids! Still, that's good guidance in general, but is rather conservative. Plants can respond to an early Spring by leafing out early, although they may get caught by a late frost. Similarly, orchids should be able to carry out dormancy and bud initiation in response to cooling temperatures and/or shorter photoperiods, in less than the full winter season. This might not serve them in a natural environment with variable weather, but that risk doesn't occur in a grow room. So, I still want to know how short the chilling and short day period needs to be.

Photoperiod - what is the appropriate 'winter'?
 

Before I grew my orchids out doors I set my grow room temp to min 60 and 12 hr grow light between Dec and Feb.
In that condition, all my nobile type dens initiated buds every year without issues.
Nobile type dens are highly seasonal growers and will only respond to a dry cool winter rest. I therefore used that as a guide line


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Two months sounds reasonable. I read that 4-5 weeks of cooling served to initiate flowering in Phalaenopsis, regardless of photoperiod. Any other bits of information out there?

A good published study by Lopez and Runkle concerning Miltoniopsis showed best blooming with 4-8 weeks of short days followed by 8 weeks of cooling. In my indoor plant room in which I have control of day length and temperature, a do one month of shortening days and then bring in the cooler days and nights for 2 months during which the days are still shorter. Then I lengthen the days and increase the temperatures.


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With my 6500 k daylight T8 fluorescent lights and s somewhat similar collection I provide 12 hours of light while indoors. At times, I have provided more, or less, artificial day length. Growth seems better with longer day length.

Different orchid genera require different conditions to initiate blooming. For example, Cattleya labiata initiates blooming in response to short days. However, most Phalaenopsis aren't affected by day length very much, but do require an important drop in temperature to initiate blooming. The Miltoniopsis study I noted showed that day length and temperature mattered for this genera. Orchids that naturally grow close to the equator don't have much variation in day length and maybe range from 11.5 to 12.5 hours throughout the year.

Unless you have multiple indoor rooms or multiple greenhouses, you can't give different day lengths and temperatures to different orchids very easily. Since I am growing Cattleyas, Phalaenopsis, Paphs, Phrags, and Miltoniopsis, I need to give a period of both short days (for me this is 11 hours) AND cooler temperatures (for me this is 55F - 70F) during a 2-3 month period in late fall to meet the requirements for everything. Some of my plants wouldn't need the shorter days and some wouldn't need the cooler conditions, but they have to put up with it so that some others will flower.


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Thanks for the informative answers. Except for a few plants I keep at a window - which gives me the local short days and cool temperatures all day in winter, I have my collection under stricter control. In winter this has 58-60 degree nights and days running 72-78. I've been giving this lot 12 hour days for 3 months in winter but believe I could get better growth for most of the plants with longer days. I think I'll try the conditions used with Miltoniopsis (although I don't have this genus!), starting winter with 4 to 6 weeks of short days, then returning to longer days but with the low night temperatures I've been using.

My Phals just bloom reliably, and seemingly on their timetable. I don't do anything except water and feed.

just to add some thoughts/notes...

Orchids can be a bit mysterious so really there's no hard rules really... certain species and hybrids certainly need seasonal variation, I for one try to focus on plants that I grow indoors that do not need variations. Besides nobile dens and phals that flower better and reliably with some cooling (and even that can be minimal), many widely available hybrids and species don't absolutely require the variations.

Consequently, with looking over posts of various species/hybrids of blooming plants over various forums online, you can take note of date when someone posts and you can see that certain ones apparently bloom at all times of the year... on other hand you can also see when a certain species/hybrid appears to bloom at a certain say 3 month period for most people posting pictures of the plant... this suggests that with variation of conditions of culture the plant may be adaptable and bloom only when it then feels like it. In certain species, like rupiculous laelias and especially their hybrids or cattleya walkeriana for examples, seem to bloom around the clock and multiple times per year, this may be probably most possible with less seasonal variation, i.e. indoors... whereas outdoors it may be more "married" to the seasonal changes.

that said, another variable, sometimes but not always, a plant that doesn't bloom but is getting all cultural needs stably, playing with daylight hours and temp drops, and lesseninging water and such- something to sorta kick them in the butt for a second, can push a plant to flower, after all a little stress, as they say, pushes a plant to think it needs to procreate and thus flower...

This is a great discussion. This is the third year of growing orchids under lights for the winter and I have just begun growing other plants under lights as well. This year, I plan to continue to grow most of my plants under lights. I still have a few orchids and plants in the windows but I am thinking of putting lights over two of those windows for those sets of plants and just having the one window light free.

Looking over my list of orchids, I discovered that most of my orchids are in the Cattleya family with Bulbophyllum, Angraecums and 'Pleuros' making up another third. The rest are odds and ends, mostly with one or two of each group. The 'warm-growing' 'pleuro' group won't like to get too hot so I won't have them under lights for the summer. I have the cooler winters but it will be interesting to see which ones need changes in lighting to bloom.

With my other plants, most of them are fine with growing under lights. I will need to see about the figs.

Growing under lights is fun, especially in winter! Love to see growth when everything is gray and brown outdoors.

When we shorten days and cool things down, most growth slows so we need to be careful and water/feed somewhat less during this time period as well.

Other work by Lopez and Runkle with Phalaenopsis showed that keeping day time temperatures 70F or less was maybe the important variable for spike initiation. I know others have said that just lowering the temperature by 10 degrees might do it, but for me, I run 84F peak during my summer months and know I can't get my Dendrobium nobile or Miltoniopsis to bloom without 55 degree nights, so settled on 55-70F for the winter temperature range. There are many hybrids of things that are less fussy about temperature or day length and a person could build a collection with things that didn't care. I wanted to have a varied collection and tried to come up with a scheme that would bloom a variety of things without really hurting anything.


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Though I use supplemental lights, the seasons are what they are and so I follow them. The supplemental lighting is cut back a bit for winter, but I always keep it at about 13 hours + or -.

Yes, that's what I do too.
In winter my cool growers are at 12~15 ºC (54~59 F) most of the time. My warm growers are at 15 ºC (59 F) by night and 22 ºC (72 F) during the day.
In summer almost all the house is between 24~28 ºC (75~82 F) most of the time.
I guess people living in hot summer climates find it easier to have blooms since the diferential is more noticeable.

The seasons are what they are, but they don't have to be. Witness growing southern hemisphere plants in the north where they adapt to our seasons. Plants have capabilities to perform 'better' where environmental factors allow them to, and (under lights) we largely control that environment. The reliance of plants on seasonal triggers, such as lower temperatures and shorter days is adaptive to the suite of conditions associated with those triggers in the natural environment. But it's not adaptive to my grow room, where I will not freeze them or desiccate them. I want to reduce the low-growth circumstances to the minimum needed to trigger blooming or new growth.

That is a good way to think of it. I have a guava getting ready to bloom, am harvesting herbs and strawberries, I have some limes growing...in the middle of winter. :)

I found the first year, when I still had the large Cattleyas, that some of my species orchids that normally put out just one set of growths started a second round under the lights. My smaller Cattleyas tend to just keep pushing out new growth and bloom under the lights. However, I am not sure if these ones have an exact season. In the windows, everything tended to rest at this time due to the lack of proper light. For the window-growing plants, I see a slow-down in growth with everything except the passiflora (of course, I want this with the Venus fly trap and pitcher).

Basically you want to do what fruit producers already do, such as producing strawberries in winter and oranges and grapes in summer (for ex.).
The difference is that they already know what to do.
I think you should look genus by genus, specie by specie.

I'm skipping over most of the discussion and am addressing the OP's original question.
I grew orchids for over 10 years with no artificial lighting at 61°North.
That translates to 19-1/2 hour summer days and 4-1/2 hour nights. Winters were the opposite with 19-1/2 hour nights and 4-1/2 hour days [at the solstices].
Except for a Catt. maxima, I avoided hight light orchids like Vandas and Catts. Although, others didn't and were successful with them.

Some were very problematical.
Bamboo Orchids [Arundina] were very difficult to bloom.
But, I could do it.

I never had problems with Dendrobium, Oncidium, Phaius, and other species plants that supposedly needed high winter light. All I had to do was follow the cultural requirements for each of them while tweaking temps, water and feeding.

Very interesting. My original question was how short a time could I supply 'winter' light, and temperatures for that matter. Your far-north winter had very long nights, but these were still over a period of about 3 months, I presume. With supplemental light could you have had successful blooming, dormancy, and more rapid growth?

That's a one time acclimation. Once such plants are adapted to the seasons of the opposite hemisphere they completely "forget" about the seasons of their native hemisphere. And how great of an acclimation it is depends highly upon the seasonality of the specific plant. Acclimating tropical plants found near the equator to the opposite hemisphere is practically foolproof. Acclimating ones that seasonally die back to the roots is a completely different kettle of fish.

Double post

Light decreases from the autumn equinox [mid Sept.] where the day is split evenly at 12hr each for day and night.
Then, from the winter solstice [mid Dec.] where the day is split @ 19.5hrs/4.5hrs day/night, light increases the opposite from the winter solstice to the spring equinox [mid March].
At the mid point between the equinoxes and the solstices the day length is changing at 5 to 7 minutes a day, decreasing in the fall and increasing in the spring.
Tropical plants usually prefer a 12hr/12hr day/night cycle.
I think they might be considered light starved for as long as 4 months or more at that lattitude.
I was able to successfully grow and bloom regularly the cool dry rest type Dendrobiums that supposedly required high winter light to be able to bloom in the spring, February and March.

Many [several?] people in that area did use artificial lighting to good effect.
It made growing Vandas and Catts much easier.
Because I grew in my living room, I refused to use artificial lighting.
I wasn't going to have large HO fixtures or other high intensity lamps hanging all over the living room or have to wear sunglasses at night to watch TV or a computer monitor.
Some things I just will not do for the orchids.

Exactly; we grow orchids for our pleasure, not industrially. The lights I currently use are 100 watt equivalent LEDS, warm and cool white, so they are not blinding (especially since they are in reflectors), but nicely warm the grow room during daylight hours. I keep the TV and computer upstairs, where humidity is lower too.

I quite enjoy the fluorescents...our dim winter days now seem as bright as summer and it takes the chill out of the room. :)

As an after thought, I'd like to add the following:

I have grown a number of plants at one time or another where consideration for their reaction to photoperiodicity was required to carry them through their life cycle.

While not having explored this more than just mentally noting what seems to have been their reaction to changes in the photoperiod, my feeling is that, at least for most orchids, worrying about the photoperiod is a non sequitur.

Too much or too little light intensity is a primary concern.
Length of day is of little, if any, concern for orchid cultivation, at least for most orchids.

While orchids are found from the tropics to the Arctic, maybe even the Antarctic, day length seems to be of little concern to them.
With little doubt, they originated in the tropics under fairly consistent evenly split day/night periods.
All recommendations for orchid day length I've ever seen have suggested 12 hour days +/- an hour or so.

JMO and I am open to more knowledgeable opinions.