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Does a seedling require the same temperature as before it germinated?

Posts: 55
Location: West London, UK
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Evening all,

I wish to prioritise the warmest highest levels in my polytunnel and I was wondering if it would be OK to drop a few levels the seedlings which have emerged and replace them with newly sown seeds?

I say this because I am wondering if the seedlings can handle slightly cooler conditions as I can recall reading a seed packet some time ago which stated different temps (highest required until germination) on it.

Does it relate to specific plants or is there a general consensus for a higher temp required for germination?

Thanks for your help (if you can understand what I am getting at!),

Posts: 2679
Location: Phoenix, AZ (9b)
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Hi Samuel:

I think you'd be ok to swap out the seedlings for a cooler spot as long as it's not a HUGE difference in temps - a few degrees isn't going to hurt them.
Posts: 3999
Location: Wellington, New Zealand. Temperate, coastal, sandy, windy,
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I'm not talking proper warm weather plants here, only tomatoes in my temperate climate.
I grow quite a few tomato seedlings for sale, and need to start them early to have them big enough on NZ's traditional planting weekend.
Nights are still pretty cold in early spring here-but we're talking NZ cold, so above freezing.
You shouldn't be too cold in the UK though...
I use a heating pad set around 18 Celsius/65 Fahrenheit to germinate, and as soon as they're up, they go in a cold frame.

In my experience, once a plant's above ground, the most important thing is having it in as much strong, direct light as possible.
Insufficient light and plants are always a bit pathetic, skinny and 'stretched', whereas if they're too cold, growth just slows till they warm.
Tomatoes are special: they grow 'adventitious' roots and it's generally encouraged to transplant them right to their top leaves.
A bit of stretching isn't the end of the world.
So in a really roundabout way, I'm saying if the plants aren't tropicals and there's really good light, I'd say you should be fine
Posts: 1528
Location: zone 7
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i germinate my plants in an unheated greenhouse. in this greenhouse is a smaller greenhouse type box. inside it is a heat cable. i use this to germinate my plants as higher constant temp gives a better germ rate and speed. once they are germinated they go into the cooler greenhouse where night temps that get low keep them from stretching and becoming lanky plants.

so the answer is yes as long as there getting good sun after germination.
Posts: 7422
Location: Ozarks zone 7 alluvial,black,deep clay/loam with few rocks, wonderful creek bottom!
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all good advice above
For awhile now I have been paying much more attention to optimum soil temperatures for seed germination...especially the things that I start in my living room.
As soon as they emerge and have their true leaves they are off to the the kitchen where the sun is and much cooler temperatures...we don't have a greenhouse.
I had a chart once that listed a lot of different seeds and the best temperature to germinate them...here is a link to one...here I do remember that many of the temperatures were much warmer than you would expect the plant to do well at...lettuce was 75 degrees F and several things were listed that you would consider cool weather plants but germinated best at warmer temperatures.

good luck!
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