Drainage and grading problems are a common issue faced in every landscape. I have witnessed many situations where plantings failed, basements flooded or lawns turned into mud puddles due to improper grading or soil settlement. Correction of drainage and grading problems during the initial phases of landscaping is crucial for a successful garden.
Plants require air exchange within the soil for healthy root development. Soils which are waterlogged lack oxygen and can cause root-rot and the decline of otherwise healthy plantings. A common mistake is amending the soil within the planting pit and/or setting the plant too low in the planting pit. The planting pit will collect water and the roots can potentially rot. A better solution is to rototill soil and add compost and/or topsoil to raise the entire bed area four to six inches. This allows the roots to develop in a well-drained medium.
Poor grading around the house can be troublesome. Settlement around the foundation can cause water run-off to pool against the walls of the house. Over time, the water can make its way through the basement walls causing water damage and mildew to grow which is a source of allergic reaction for many of us. If puddling or erosion near the foundation walls are apparent, an inspection from the top down should be the first action. Are the gutters in disrepair? Bent, corroded or misaligned gutters can leak badly during rains. Gutters can pull away from the house trim and can allow water to runoff behind them. Downspouts can become blocked with leaves and debris causing water to fill up in the gutters and overflow into beds. If splash blocks are in use, are they sloping away from the house? Many times, I have seen settlement of splash blocks with turf or mulch damming the water and causing it to empty back against the house, read more here.
Next time it pours, get your umbrella and make an inspection of your gutter system. The results may surprise you. Having corrected gutter/downspout problems, the next line of defense may be to raise the soil level near the house. A good rule of thumb is to raise the soil to achieve a 5% slope away from the building line. Of course, soil should not be raised too near to siding to prevent termite problems. If serious water problems are present, a thorough inspection both inside and outside of the home is warranted. Waterproof membranes applied to the foundation, extensive drainage systems or major regrading may be required. Your professional landscape design consultant can offer solutions to most of your drainage and grading problems.