Mature rhododendrons can grow quite large and take up a lot of space in one's garden. Some varieties, like "English Roseum," can grow up to 8 feet tall and 8 feet wide. Transplanting mature rhododendrons can be done as long as you can handle a little hard labor. Rhododendrons do not have deep root balls, but they are wide. Also, mature rhododendrons are quite heavy to lift up and move so you will need a little help.
Choose a new spot in your yard for the transplanted rhododendrons. Rhododendrons need partial shade and acidic, well drained soil.
Prune back the mature rhododendrons before you transplant them. Cut away all extraneous growth around the sides and base of the rhododendrons, leaving only the main branches. Cut off 2 feet of top growth as well.
Dig holes around the mature rhododendrons with a diameter of 6 feet and a depth of 1 foot. Loosen the soil until you can position the spade under the mature rhododendrons. Lift up the mature rhododendrons and place them in the wheelbarrow. Loosen the mature rhododendrons root balls.
Dig new holes for the mature rhododendrons. Dig holes as deep as the root ball and twice as wide. Add a mixture of equal parts compost and peat moss to the hole and work it into the soil. Add 2 to 3 tbsp. transplant fertilizer to the holes and water them until the holes are full. Allow the water to drain.
Place the mature rhododendrons in the holes and water them until the holes are full. Allow the water to drain and cover the mature rhododendrons' roots with soil until the holes are full.
Apply a 2-inch layer of mulch on top of the soil.