Plant an oleander tree in a warm location with plenty of direct sunlight either in the spring or the fall. Only plant an oleander tree outdoors in areas with a minimum temperature of 10 degrees Fahrenheit. Otherwise, plant the tree in a pot that can be moved indoors during the winter.
Select a planting site for an oleander tree that receives full sun and has plenty of room for the shrub to grow, as it can reach up to 20 feet tall. Although the plant thrives in a multitude of soil types, from sand to clay, it grows best in a soil pH of 6.5 to 7.5. Plant the tree in the evening, or on an overcast day without wind, to keep sunlight and wind from drying out the roots. To keep the roots moist, leave the root ball bundled in burlap until it's time for planting.
To plant the tree, dig a large hole that is three times wider than the root ball, and then remove the burlap from around the tree. Place the root ball in the hole, and fill in the soil. Build a small hill around the tree to hold in water. For a potted plant, combine one part sand, one part perlite and nine parts potting mix in a large container. Water the oleander at the base of the trunk immediately after planting.