if a plant is growing in a pot then you can plant it into the ground any time providing the ground isn't frozen. dig the hole bigger than the pot it is coming out of. loosen up the excavated soil adding a bit of compost to it to help break it up and give the plant an in between soil. plant and water well for several weeks. if the roots are taking the shape of the pot then losen them a little to help the plant grow out into the soil.

Do you mean sorberia? If so be warned it runs and will need either containing or regular removal of suckers. If there is a sobia plant I apologise!