Grow lightscan they stay on 24 hours?

I'm starting my seeds under lights, and I'm inexperienced. Can I leave the grow lights on for 24 hours, or do I need to mimic the usual daylight/night-time pattern by using a timer? I've followed the directions as best I could regarding sowing some seeds on top of the medium, and some under it.

use the timer.

Yes, they need the darkness. If you keep them on 24 hrs. you will alter their natural growth process and they will be weaker. They need to rest, plus plants still 'respirate' at night. 14-18 hrs. will be fine. (I actually have mine on 12)

Thank you for the information! It seems logical that I should use a timer to replicate nature. . . . but I didn't really know why. I appreciate the advice!

I also have mine on for 14hrs, but the plants, flowers under the street light out side look to be doing very well ? ?

Yes, plants do need darkness to grow.

In the photosynthesis process, there is a reaction known as 'dark reaction' or sometimes known as 'carbon reaction', a very important process to release oxygen into the air. This happens in the dark or at night.

Darkness is also necessary to induce the plant to initiate the flowering process. This is known as photoperiod, and is based on the ratio of the day length to night length over 24 hours. Plants use the photoperiod to determine the time of year. The changing day/night ratio synchronizes plants to their environment. In this way they progress with their life cycle in coordination with the seasons.

Most plants cannot properly mature without the proper environmental cues, and they become confused. Plants often use dark time to build up florins which are hormones plants use to bloom. This is why light is reduced to 16 - 18 hours for day neutral plants. Short-day and long-day plants are much more specific in their dark period requirements to flower properly.

Plants reaction to photoperiod can be divided into 4 groups.

a. Day-neutral plants - the plants has no effect on photoperiod. They will flower when the plant reach physiological maturity.

b. Short day plants - plants will only flowering when day length is shorter than night length. This group of plants will only flower in late summer or fall or very early spring, when day length is shorter than the night period. e.g. strawberries, potatoes, chrysanthemums etc.

c. Long day plants - Plant that flower in spring or early summer. Flower initiation will begin when the day length is getting longer than the dark period.

d. Intermediate day plants - These group of plants will grow vegetatively when day length is too long or too short. However, they will only flower when the day length is about 12 hrs of daylight and 12 hrs of darkness.

All of this is just a little background on why plants DO need a period of darkness, and most of it the average gardener doesn't need to be too concerned with when it comes to starting seedlings. If you give them about 8 hours of darkness to start off, they should be fine and will acclimate once they are planted outside.

But Joan, how about the plants under the street lights.
I know street lights are not the same as daylight,
But you can read a newspaper under them.
So I believe plants can adjust to the light they have.

Don't know. Maybe the streetlight beam is indirect and low enough that it doesn't affect the process. Nothing I have says that it has to be pitch dark, but I can't find anything that says really how dark it needs to be.

I suspect most times the outdoor lights are far enough away from the plants that they don't do much harm. But indoors for seedlings, if you've got your lights at the proper distance from your plants (no more than a few inches above the tops of the plants) then the seedlings are getting a higher intensity light than they would from a street light that's many feet above them. Some plants are also more adaptable than others but I'm a big believer in mimicking nature when you can (plus you'll save on your electric bill if the lights aren't on 24-7)

Daylight is the best, I've put my (to be) transplants outside for the last two days, they love 'Sun Bathing' ^_^

The lenght of time to leave plant lights on depends upon the variety of plants you are trying to grow. Plants that are sun lovers (Geraniums) require 16 hours of light/day. Low light plants such as (African Violet, Hostas) can do well under 12 to 14 hours.

Thanks for all the good advice. Blomma, I appreciate the distinction you made between sun-lovers and shade seedlings. Most of the seeds I'm starting are for sun-lovers.
This has really helped! Thanks, everyone.