Plant in a site that gets plenty of sun. Rainer cherries should get about eight hours of strong sunlight daily.
Submerge the tree's roots in a bucket of water for a good soaking. Never allow the roots dry out before planting. Keep them very wet as they are planted. Trees roots that have dried out should be well-soaked with water and chilled in a refrigerator or a cold outdoor spot that is about 100 degrees Fahrenheit and kept there until they are planted.
Dig a hole that is deeper and wider than the spread-out size of the tree's roots. Loosen the soil inside of the hole so that the roots will be able to expand as they grow.
Remove damaged or dead roots. Also cut back any that are more than a few inches longer than the other roots. Set the tree in the hole and spread the roots out. The graft line should sit several inches above the surface of the soil. Fill the hole partway with soil, add several gallons of water, and finish filling with soil.
Prune the top of the tree back so that is about two-thirds of its original height. This helps to compensate for root loss in the planting process and begins to train the tree to produce more lateral branches.
Plant a companion tree simultaneously with dwarf Rainier cherry tree. The Rainier requires a pollinating tree such as Bing, Stella or Van for it to produce fruit.
Secure the tree with a strong stake to support it, especially while it is young. Dwarf trees often need the extra support that stakes provide, so use cloth or section of old garden hose to pad any wire or string that wraps around the trunk so that the bark isn't damaged.
Keep the tree well-watered during dry periods where the rainfall is less than 1 inch per week, especially once it begins to set fruit. A deep soaking once a week will help prevent stress and keep the Rainier cherry growing well. Make sure the ground immediately around the tree is saturated to a depth of several inches for best results.