First we need a definition of terms. Do you mean Cedrus or Thuja or Juniperus?

tj

the common name cedar can mean various conifers.. so it would be best to ID exactly what you are thinking about ...

conifers are trees.. and as such.. never really stop growing ... especially at some magical height ... you either pay big for dwarfs that grow at a reduced annual growth rate [which take a longer time to get to height] ... or you start shearing them ... to maintain the size you want ... the only other alternative is bonsai .. in the sense that you root prune them every year.. to make them grow slower ...

there is a container forum ....

the media... is the most important thing in the pot... trees prefer a sip of water.. and then high drainage ... so you dont want the usual media for annuals and perens that are water hogs.. you can start with that.. but then you add things to create what you need... im sure al will roll thru and boggle your mind all about that ... of course.. being in most likely full sun.. and higher winds.. you probably need to hone the media to account for such .... dont forget hot sun on a black pot.. heats the pot.. and roots dont like to be hot.. and it can change watering needs ....

you are about the 3rd little momma to roll thru over the years with plans like this.. all the power to ya.. but i often wonder how it all works out ... creating a garden that will require vast long term care.. might be akin to walking in the door with a puppy and saying good luck for the next 16 years ... lol .. make sure your son wants what you are offering.. before you invest in such ... this isnt going to be a plant/pot them up.. and forget about them forever ... it wont be a big burden.. but he just might not be as excited about it as you ...

ken

ps: ive never gardened on the roof... but i always wondered about water damage possibilities.. and how peeps deal with such ... im sure its not a big deal.. but it is a non-gardening variable to think about ...

ken

On the west coast, the term 'cedar' will most often be applied to Thujas/arborvitae (if not true cedars/Cedrus species, none of which would be appropriate for container culture). Arborvitaes are rather common container plants here but with 5' as a height limit, I'd focus on dwarf selections........ Thuja occidentalis 'Teddy' comes to mind as being nearly ideal for the OP's purposes, provided local availability.

There is an excellent, long running post in the Container Gardening forum about growing trees in containers that is worth reading in some detail: https://www.gardenweb.com/discussions/1389927/trees-in-containers-iii#n=230

Hi Garden Mist!

Here's a link to the American Conifer Society article on 'Rooftop Gardens'. It might help you get some ideas. :-)

https://conifersociety.org/conifers/articles/rooftop-garden-conifers/

Thank you everyone for all your wonderful advice. After doing some research, I think one kind that might work would be emerald cedar. Not sure though, I'll keep looking. All I know is that he wants 3 cedars in pots. lol

Thanks Gardengal, hmm...wondering about a dwarf type cedar or spruce?