I'm looking where to put a bunch of seedlings, but there is a power company street light there that goes on at dusk and off at dawn.

Do daylilies need darkness at nights?
(Think I've read about plants that do need darkness at night.)

Pat, you are correct, some plants need full darkness for a certain number of hours in order to bloom. For example, poinsettia growers have to use black cloth to insure longer nights to get them to bloom for Christmas by simulating shorter days than naturally occur at that time.

I have only ever heard of this being an issue to get them to bloom, and not to grow. Many daylily growers using artificial lights and timers give their plants extra long days to get more growth and more compact growth in seedlings.

Some plants don't use day length to determine when to bloom in season, but wait on soil/air temps to reach a certain point for a length of time, or cold weather for a certain period of time. This is how many spring flowering trees 'know' when to bloom. If you read a quality fruit nursery catalogue, you'll see 'chill hours' given for peaches. This tells how many 'hours' below a certain temperature they need to bloom out. If you plant a northern peach in the south, it will never get enough chill hours and won't bloom properly.

Bottom line...different plants have different ways of deciding when to bloom. To the best of my knowledge, daylilies bloom when they reach a certain maturity level and the soil and air temps are consistently warm. This is why they bloom early in the south and progressively later in the north as the season gets warmer.

We have a dawn-to-dusk street light across from the house and it has had no effect on bloom. I think your seedlings will do fine, even with a light on them at night.

Other opinions?

Thanks, Bob.

I would have to say no to that question. I live on a corner that has a streetlight. I have daylilies planted in my front yard that are exposed to that streetlight and I have never had any problems with them blooming.

There are different types of street lamps and they affect plants differently. I have two street lamps near my house. One by the road and one on the side of the yard. I have noticed the crape myrtles seems to be affected but have not really noticed the daylilies near them being affected.

I have a street light in the back yard and have not bad any problems with blooming. The light intensity near the ground doesn't seem like it would be enough to really was with the photoperiod of the plants. Certainly isn't enough to coax pollen sacs open.

Xenacrockett said:I'm looking where to put a bunch of seedlings, but there is a power company street light there that goes on at dusk and off at dawn.

Do daylilies need darkness at nights?
(Think I've read about plants that do need darkness at night.)

My totally uneducated thought is that daylilies, like all plants, need light from a certain spectrum - a spectrum not given off by streetlights of any kind. FWIW

Pat is correct that some plants (e.g. tomato) are damaged by continuous light. However, some people keep their daylily seedlings under 24 hour lighting and don't report any problems. As far as flowering initiation is concerned, daylilies are considered day-neutral and therefore not affected by daylength aka photoperiod. Daylilies are popular in commercial landscaping such as around parking lots and other areas with night street lighting and that doesn't seem to bother them.

As far as other plants are concerned, yes some are affected by street lighting but it depends on the plant and the type of lighting. It's more likely to affect photoperiod responses, which primarily react to red light (such as from an incandescent bulb or high pressure sodium). The light intensity to affect photoperiod response doesn't have to be anywhere near as high as for photosynthesis, in fact it can be quite low, as little as 10 foot candles.

Edited to add BTW the wavelength range for PAR (photosynthetically active radiation) is around 400 to 700 nanometers).

Ut oh, now I have an itch to learn about those things and understand! @sooby

-- Photoperiod is day length of light ... got that, I think

-- Daylilies are not impacted much by how long or short they are exposed to daylight (photoperiod), so that is not a primary way that they know what season it is, or when to flower.

-- other plants that are sensitive to amount of daylight for knowing season and when to flower (like tomatoes?), can be impacted by lights from sources that produce light in the red range of the spectrum. That can include incandescent and high pressure sodium lights. Incandescent examples might include (high intensity?) household lamp lights (old or new compact bulb versions), and high pressure sodium lights may be found, for example, near streets or parking areas and used as flood lights, security lights, and also in plant grow lights.

-- The amount of light that would impact plants that are sensitive to daylight for season/bloom can be as little as 10 foot candles. Very roughly, equivalent to 10 candles burning at the center of a circle that is one foot in radius wide? So those sensitive plants, like tomatoes, can be impacted even with low levels of incandescent or high pressure sodium lights.

-- Photosynthesis that plants need for energy takes more than those 10 foot candles. The full range of light that produces photosynthesis (PAR) is 400 to 700 nanometers, which includes all light visible to the human eye, and that must be stronger than the 10 candles in the one-foot-radius circle to enable photosynthesis to take place.

I am sure I've got some of it wrong, but I love to learn new words, try to sharpen understanding of familiar words, and then see if I can say back what I think I learned.

I think you've got most of it Because daylilies are day-neutral for flowering doesn't necessarily mean they don't respond to photoperiod for other things, though. I'm thinking of things like dormancy, which may involve temperature, photoperiod, or a combination of factors, but daylily dormancy isn't well understood.

Tomatoes are also day-neutral for flowering. What I meant by continuous light damage was physical injury, such as chlorosis, stunting, necrosis (in those plants like tomato that are sensitive to continuous light).

Plants that are not day-neutral for flowering are either long-day or short-day plants. While the terminology suggests length of day, the plants actually measure the length of darkness. Ten foot candles is the minimum you would want to supply artificially from an incandescent bulb to influence photoperiod.

For maximum photosynthesis you'd be looking at somewhere between 500 and 3,000 foot candles, depending on the particular plant's tolerance. Bright sunlight can give much higher intensity than this but going above the plant's upper limit (light saturation point) won't further increase photosynthesis.

Thank you so much!

I sense a whole new area of exploration catching me up into learning about daylilies (and other plants) with regard to dormancy and photoperiod, as well as photosynthesis, sunlight intensity and light saturation point (if there might be some injury impact at some level similar to that of continuous light damage).

I'm off to explore with Mr. G!