If you don't keep your home very warm (< 20C?) I think it will be ok inside.
They grow fairly fast for a pine so you might as well plant it outside in early spring.

I don't think they are typically seen in the "zone 7" parts of France. (They are very common in the milder parts...zn 8, 9 & 10) So that's something to think about...if you get unlikely and have a cold winter before it establishes fully, it may not make it. Perhaps helped by our very hot summers, they have generally proven to be hardier in the US SE than they are rated in Europe. One survived -22C in North Carolina. You should consider it experimental if you don't see them around. (S'ils ne sont pas trouvés dans votre ville, ils sont experimentales...c'etait un arbre tres populaire d'antan)

Yes - I think it would be highly experimental in Lorraine. They don't even grow well in most of the UK away from the South.

I don't see a lot of them near my "région" but I hope it will make it ! :D Thank you for your answer ! :D

So, will it be ok if I just keep them inside one-two months at 60-70% hygrometry at a temperature of 21-23°C during the day and 19-20°C during the night ? (just the time for the seedling to be stronger). (Just a little precision, they are in 65-70 % of perlite, 25 % of special sowing soil and 5% of coconut fibers.)

I was assuming you had a 1 or 2 year plant, as are sold by the millions for tiny Christmas trees.

If they are just-germinated seedlings, wait until later in spring to plant them out. And you should certainly consider waiting until the following year to plant all of them outside. In other words give them another winter or two inside to size up. A Pinus pinea that survived about -18C for me was already 1m tall and perhaps 3-5 cm trunk diameter. It was on a south facing brick wall; our winters are sunnier than almost anywhere in France. Forestfarm (US nursery) said at the time (early 1990s) those seeds came from a very hardy tree in Seattle, WA. Interestingly that winter outright killed a slightly smaller Quercus ilex; IIRC that oak is considered hardier in the UK than the umbrella pine.

Do these pines need a cold winter ord should they be ok at approximately 15-18°C under horticol LEDs ?

My thinking on the matter is they come from extreme southern Spain where winters are quite warm. And, the reason they are grown for pot plants by the millions must be that they don't mind being in a greenhouse for the entire lives. So overall I think compared to most non-tropical pines, no, they don't need much winter chilling and you should be ok. That being said I've never raised them myself and don't know what to expect.

Ok, thank you for your help ! :D

I hope it will work.

I'll update this topic with some pictures. :p

Any other answers or informations are still welcome.

Forestfarm (US nursery) said at the time (early 1990s) those seeds came from a very hardy tree in Seattle

Presumably the basis for this was the (coldest in 30 years) 1990 winter, during which scorching of Stone pine was general here (USDA 8). However I do not recall seeing any established trees die. So I have to wonder how any individual here was identified as being more hardy than usual.

One 50 ft. tall (ca. 2005) in the Seattle arboretum had an accession number indicating it was acquired in 1966. Eventually it lost a big branch, and I think was removed - the online University of Washington Botanic Garden database does not list the species as being in the collections at this time.

Thank you for your answer. ^^

So how many time should I keep them indoor ?

Sincerely,

Jack,

if you are keeping them indoors due to cold.. then they should stay inside.. until the cold is past ... dont you think ...??

how that all works out in your area... is left to you to figure out ...

and do keep in mind ... as spring warms ... they could go in a shed or garage ... if day temps are good.. but nights may not be ...

when they do go outside ... i would put them in bright full shade ... for most of the year ... though full sun plants ... trees in small pots .. or even trays ... can be very problematic to keep properly watered ...

proper watering is most likely .. your most important variable... IMHO ....

some pix would really help us understand your project ...

and finally ... if you have many .... then try different things ... odds are.. you will get lucky ... but if you do them all the same ... then you either win or lose on one throw of the dice ...

ken

I am having a punt on them. Got tiny seedlings in the greenhouse. I was going to keep mine in pots for a few years until big enough to survive an East Anglian winter. I have seen them on the east coast so think the relatively dry climate of eastern England might be OK.

I have had a labellng disaster with the others though - got a range of pinus growing (so cute) but owing to the collie's habit of removing labels from pots, I now have no clue what any of them are - will no doubt be posting pics on here.

Ah, I suspected as much...but never mind, whatever comes through the testing ground of my small garden, and inconsistent attention, will be proven survivors and definitely more likely to cope with the benign (by comparison) environment of the woods.

Thank you all for your help ! :D

I'll keep them near a sunny window with some artificial light.

I will bring them out in approx one month.

How many times should I water them ?

(Right now I water them 1-3 times per day with a water spray, only the surface is wet)

Sincerely,

Jack,

Well mine are in my cold greenhouse and I water them about once a month (if that) . ..but as they are only 3inches tall, it is not like there is much transpiration or evaporation going on. I have no clue as to your circumstances but watering everyday sounds wildly excessive, particularly since these pines are habituated to drought. I actually don't really see much point in wetting the surface - this tends to give me a false reassurance that all is well (and causes surface moulds and algae) but tipping out the pots shows total dessication around the root zone. I would suggest sitting the pots in a saucer until no more water is taken up, then drain and leave (making a rough note of the weight of the pot) - one of the ways i assess watering needs.

I really don't care for growing things under lights or using extra heat as the transitioning to outdoors can be fraught - hardening off process takes at least a week or so, sometimes more - I have played the in and out game with seedlings too many times in the past and now prefer to either treat them mean from the off or desist from temperamental types.

Ok, thank you for your help ! :D

I now water without spraying to avoid damping-off and I don't water until the soil dry.

And I will bring them outside in march.

Is that good ?

Will everything be alright if I do like this ?

Sincerely,

Jack,

(temperatures are between 18 and 20 degress during the night and between 21 to 24 degrees during the day)

Yes...but the bringing them outside can be critical - you might have to put them out in the day and bring them in at night and placing them in the right place (I put mine down the west side of the greenhouse). How old are yours, Jacky? Mine are a year old and between 1 and 3 inches tall (the lacebarks are the smallest). What are your plans for yours?

I plan to keep them in a pot for a few years and in 10-15 years I'd like to plant them outside.

Mine are à few days old ! :P

In how many days will they be adapted to the outside conditions if I bring them out in March (night and Day) ?

Usually, hardening off can be done in a couple of weeks (I have forgotten about mine though after only a few days) and it does depend on the plants themselves. Tomatoes, for example, can go through an endless 6 week period of night-time protection...but with trees and shrubs, the scouring outside sunlight can be more of a shock than night-temps. Anyway, yours are so little, you could be moving them in and out without much hassle - aim for a 2week hardening off process and keep an eye open for big temperature fluctuations. I dunno where you are - in the UK, the climate is generally temperate without massive changes across the seasons...and the vernal equinox acts as a handy time-frame that all hardies should be installed outside by then.