In extreme cases, you may have to install a drain tile to help carry water off the site. In shaping the final grade, avoid leaving dips or pockets where water is likely to stand. Shape beds so that excess water will be carried off the site and away from buildings. Water also can be directed to unplanted areas. Few ornamental plants, with the exception of pond plants, can tolerate long periods of standing water.
Good drainage is critical for most ornamental plants.
If you are planting around new construction, remove any debris left on the site that may cause plant growth problems. Chunks of concrete, roofing shingles, globs of tar, oil spills and sheetrock are a few of the hazards of new construction sites. These can result in long-term growth problems. In addition to examining the physical properties of the soil and taking corrective measures on poorly drained soils, a soil test will determine which nutrients need to be applied and whether you need to adjust the pH. A soil sample is best taken several weeks before planting so you will know how to treat the soil at planting time. However, if new soil is brought onto the site at planting time or if soil is moved around during the final grading, it is best to wait until all the soil is in place before sampling.