Washington Hawthorn trees thrive in full sun, which includes at least 6 hours of direct sunlight a day. They like well-drained soil but can grow in clay, loam or sand with care. Water frequently until young trees are established after that apply the least water necessary, especially during periods of drought. Mulching around the base will help to keep soil moist and prevent weeds from growing. Pruning to open up branches and remove damaged or crowded branches can stimulate healthy growth and promote better air movement through the tree.