Plants differ in the amount of water they can tolerate in the soil on a constant basis. Saturated soil that is low-lying, waterlogged and swamp-like might be ideal for one plant and quickly kill another. Good drainage is important for most plants to prevent starving the soil of oxygen and preventing root rot. Drainage can be improved by physical placement of plants where moisture content in the soil can be controlled and by amending the existing soil to boost its draining ability.
Plant on high ground where irrigation and rainwater flows away and down from the plant and refrain from planting in low-lying areas where surface and underground water will naturally pool.
Create a high-ground planting site over moist soil where there is not one naturally. Add sufficient soil to raise a planting area by at least twice the depth of your plants root ball. Plant your tree, shrubs or other plants in the raised-soil area to control the amount of water the root are exposed to.
Amend the existing ground soil with several pounds of builder's sharp sand or very coarse sand to increase the flow of water through the soil. In heavy clay soil with drainage issues, the sand should be mixed with even amounts of coarse organic material such as peat moss, aged manure, shredded bark and compost to prevent a hard cement-like crust from being established in the soil between the clay and sand.