Some considerations before planting an oleander tree are if there is a good location for the tree with full sun, if it is a good time of year for planting and if there is sufficient room for growth. Because the tree is poisonous, avoid planting it where animals or children have access to it.
The best time to plant an oleander tree is either in the spring or fall in the evening. However, planting on an overcast day is the best option so that the direct sunlight doesn't add stress to the newly planted tree. Choose a location that receives either full or partial sun with between 6 to 12 feet of space. Work organic material or peat moss into the soil to help the soil remain moist.
When planting an oleander tree, dig a hole far larger than the root ball before exposing the plants roots so they don't dry out. Remove the plant from the pot, and place the roots in the hole. Fill the hole with soil, arranging the dirt in a berm around the plant to help hold the water.
Water the tree well immediately after planting at the soil level, and once a week thereafter so the plant gets a little less than 1 inch of moisture. Reduce watering during the winter. Lightly fertilize the plant with diluted nitrogen-based plant food once a year.