How do I plant a Forsythia shrub?
Certified GKH Gardening Expert
You can plant a Forsythia any time of year that the ground is not frozen or freezing temperatures are not an issue.
Choose a full sun location with well draining soil.
Dig the planting hole at least two times wider then the root ball.
and the same depth.
Place the root ball and plant at the ground level or slightly above.
Backfill the planting hole and water.
Water new plantings well the first couple of weeks and then you can cut back.
Here is an article with more information.