I have taken cuttings of my Rose of Sharons, Weigela and Hydrangea shrubs in a clear plastic container with 2 inches of potting soil sitting below 2 inches of sand..the container has been covered with a white plastic bag and has been in a bright(non direct sunlight) cool sopt behind/underneath my evergreen cedars. I am fairly confident of root growth…it is 12 July 2019..After rooting should I leave them where they are theough winter until spring /March/April 2020?? or should I place them in pots and keep them indoors in the basement with artificial lighting until Spring 2020?
Thank you for contacting Toronto Master Gardeners.
You do not mention if you did soft or hard wood cuttings. Hard wood is usually done in the winter so I will assume soft wood.
If you have a significant root system by September it would be good to get them into the ground in a sheltered area so they can establish when it is not so dry and hot. If they do not have a good root system you could continue growing them indoors for the winter.
One concern I do have is having sand over the potting soil. Osmosis and capillary action in the soil has difficulty spreading water between different density mediums. It could cause you to have a layer in your pot between mediums that is perpetually moist and cause damage to your roots. Water does not necessarily follow gravity. It is always recommended to use one medium throughout a pot .
I am including the link below as it is an informative article on soft wood propagation.
https://hortnews.extension.iastate.edu/2003/6-6-2003/softwood.html
Good luck!