Artificial lighting

[mrellen]

I have florescent lights in my greenhouse in Olympia, WA. Does anybody have any recommendations on regulating the length of lighting throughout the year? One source suggested 12 hours in Sep and Oct and then 18 hrs in Nov and Dec to increase flowering for the holidays. Any thoughts?

[DavidCampen]

I don't have any answers for you. I just wanted to comment that this is a subject that I am also interested in e.g. the effect of day length on orchid flowering.

I wonder if a species endemic to equatorial regions would be less affected by daylength that a species from northern Mexico.

[raybark]

There certainly is no set answer that applies universally.

This may seem more knowledgeable than I truly am on the subject, so take this only as a series of potentially-pertinent comments to act as a "jumping off point" for further thought and inquiries.

•Not all plants react to photoperiod for the initiation of blooming. Many phalaenopsis, for example, are triggered by changes in average temperature.
•In some cattleyas that do respond to photoperiod, it is a reduction in day length that triggers blooming, not extension of it.
•A lack of sufficient light is often a significant contributor to plants not blooming, so if your latitude results in short days, supplemental lighting might be the key.
•Plants need a certain amount of "down time" from light exposure, so that biological processes other than photosynthesis can take precedence. I'd bet that David's supposition about geographic origin as it relates to day length is appropriate.
•You also need to consider the lights themselves - wattage, age, and distance from the plants. Most fluorescent tubes should be replaced annually, and often need to be closer than we may think. I have a 200W CFL in my greenhouse, situated in the center, about 6 feet from the closest plants, and it adds very little to the light flux even those plants see; probably nothing to most of the GH (it's fine for working out there though). I'll measure what it adds and repost later.

With all that to think about, what I have usually read is 12-14 hours on.

[jean2]

First of all you must find out what orchid you are growing and gather all the details of its requirements. This information is necessary in evaluating the amount of light and shade of your particular orchid. Light intensity is measured in foot candles (fc). On a bright sunny day in summer, the intensity outside may be as high as 10,000 fc. While the light indoors furnished by a window may have an intensity of just 100fc, well insufficient for growing orchids. In low light, the intensity should be 1200-2000 fc, medium light - 2000 - 3000 fc and in high light the intensity should be 3000 and more fc. So the minimum light is 1200 fc which is 10 times more than 100 fc provided by a window alone in the home.

[timed]

Foot candle measurement is impractical for most people. What it seems you are saying is that orchids can't be grown in windows. Many would disagree with that.

[jean2]

I never mean that. So many different orchid varieties that thrive in so many different growing conditions, it is relatively easy to find an orchid that is well suited to the conditions that you can provide light whether it is a kitchen window or a full-size greenhouse. Some are almost impossible to keep alive, much less bring into bloom—even for professional growers. But there are dozens of varieties of orchids, and hundreds of hybrids, that are perfectly happy growing on a sunny windowsill or under lights. Orchids native to the humid tropics, such as phalaenopsis and paphiopedilum, prefer daytime temperatures of 73° to 85°F, with 80 to 90 percent humidity. They are happiest in an east or southeast window where the light is not too intense.

[PortlandRed]

It depends on what you're growing. Phals can respond fairly readily to longer day lengths while other orchids are less photo-sensitive. Because this varies with species, suggest you check photosensitivity references for each of the types you grow. I know Orchids magazine has run article(s) about artificially inducing blooming in phals through longer light periods but since my memory isn't what it used to be, I can't recall just when. You might check the archives on line. As with most things related to orchids, there's just not one general rule. Good luck.

[jean2]

First of all, we should know difference between artificial grow lighting and sunlight. The difference is – most artificial light doesn't emit as much energy in the red and blue region of the light spectrum as sunlight does. The sun, a torch, and a light bulb all emit energy in the form of particles called photons. The photons from the sun are a product of thermonuclear fusion. A torch uses a chemical reaction to burn. A light bulb converts electricity to photons. But a photon is a photon – and light is light – whether it comes from the sun or a flashlight. Researchers can successfully grow plants using only artificial light in growth chambers.