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Light - heat requirements for starting seeds & maintaining seedlings?

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by Patty S on February 27, 2006 06:40 AM
I'm a bit confused about light/temperature requirements when starting seeds. Which thing is most important for germinating seeds? I know about Columbine, Bells of Ireland & a few other seeds needing light to germinate, but other than those types of seeds, is there a light (or heat) requirement for germinating seeds? ...and how about after they sprout? I bought "Grow Lights" for my mini greenhouse yesterday, just because regular fluorescents don't seem to be adequate & the seedlings get spindly & die off before they have a chance to turn into "real" plants... but at the same time, fluorescent lights don't throw off much heat!

My greenhouse is outside. Do I need to put a regular light in it at night, to try to maintain an even temperature? (I also wonder whether it gets too much heat during the day when the sun is shining on it... should I move it to a shady spot, where the temperature can be controlled better?) [dunno]

Does what ever the Sun do for plants (UV rays or something [nutz] ) penetrate the opaque plastic cover of the greenhouses? I open it up during the day when the Sun is shining, but mostly so things don't bake in there! I'm lost on this issue (or maybe its NOT an issue!) [dunno]

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by markr on February 27, 2006 07:12 AM
so many things there to cover!
i think the most important thing is temperature,
keeping and maintaining it for germination,
once it is germinated, then the temp is not so important i find, most plants can be grown at lower temps.
i think most seed packs tell you what temps they need.
some need extra heat from a propagator or heat mat,(peppers tomatoes) some germ at lower like (leeks) same for flowers! light i trie to give mine as much as possible at this time of year, ive never given mine any lights yet! but they can be an advantage in low light conditions! hope this helps a little

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by dodge on February 27, 2006 08:08 AM

UV rays from the sun is what makes everything grow.......Without sun, we would all be dead..

Outdoor green houses have to be watched very carefully. Your on the right track, open the doors for ventilation.. They will cook..

Only on cold nights one might need lights.

GOod luck

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''''Those who live in the Lord Never See Each Other For The Last Time!''''
by tkhooper on February 27, 2006 10:44 AM
I was recently reading the page Bill wrote about seedlings and was amazed to find out that most seeds are not started in direct sun. Just one of may things that I do wrong lol. As I think I've mentioned I'm a beginner with a very poor memory. But if you google starting seeds or something like that within the site you should find the page.

Although it's the most expensive solution when it comes to heat I think the mats are probably the best idea. I think they have an internal themometer that keeps them from over or under heating the seeds. I'm very curious to hear about which plants you are trying to grow. I do mine in my windows and they have all done well except for a woodrose that is tropical and requires 80 degrees F for germination.

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by rozy221 on February 27, 2006 11:38 AM
Hi Patty! I'm only a novice gardener, but so far I've been having pretty good luck with my seeds.
As far as light, I would think that you would only maybe need some supplemental lighting in the evening for a few hours after the sun has gone down.
Your main concern would be the heat-what are the temps during various parts of the day/night? I know that for vegies, the lowest nighttime temps are anywhere from 45-60. Flowers I would guess would be about the same, maybe a little bit lower.
That's for already sprouted plants. To germinate, I put my vegies on a heating pad, but not my flowers, although they're above a radiator, so the coldest they ever get is about 60 degrees.
As far as individual seed requirements, it really varies depending on the seed. Most vegies do NOT need light to germinate. Lettuce, on the other hand, does, as do many flowers. Again, in a greenhouse, this shouldn't be a problem for you.
So, I think you should closely monitor the temps in your greenhouse-see where you're at and where you need to be and then find a reasonable solution, probably no more than a heater for a few hours every day.
Good luck and let us know how you make out!
by Patty S on March 01, 2006 03:17 PM
Thanks everybody, for your posts here. I think you've got me on the right track now!

So far, I've managed to keep the temp in my mini greenhouse above 50* F. I have a a clip-on light at the bottom of it & since it's not freezing at night now, I've replaced the 60 Watt bulb with a 40 Watt, which I turn on at dusk.

I have some seeds starting in Peat pots & have those sitting in a tray (lined with wet paper toweling) on the bottom shelf, closer to the light, where it gets about 5* warmer. (Because of the things on the upper shelves, they don't get any light from the Grow Light at the top of the enclosure, but they won't need that anyway, until they sprout.)

We've had scattered showers lately, with the outside temperature at 50-70* F, and the Sun peeks through the clouds now & then, so I unzip the enclosure during the day.

With a Cottage cheese container of water at the bottom, near the light, plus a daily misting of the seedlings, I'm able to keep the humidity fairly high so nothing can dry out. Plant starts on the upper shelves seem to be doing fine & aren't growing too fast/getting spindly, which was one of my concerns.

So far, I'm liking this arrangement. Thanks again!

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