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 -.