Making a Moat

• When planting trees, landscapers often erroneously will create a deep trench around a tree to hold water in it. This can be a great idea for freshly planted trees, but if the moat is not deconstructed fairly quickly, water will accumulate near the tree's base and can easily drown the tree's relatively small root system. Keeping water in such a concentrated area also discourages a tree from growing its root system outward. Using landscaping edging can have the exact same effect on water and plants. The plastic creates a very blatant barrier to excess water in a bed. That said, if the soil in the garden bed is not saturated, water should flow under and through the soil as opposed to outward above the soil. Usually if a plastic edging barrier is being used and is holding water in, the issue has more to do with over-watering or with an excessively clay soil medium.
  
  

Clay Soil

• Water does not flow easily or quickly through a clay soil. Though the first couple inches of your garden bed may be thick and loamy, if a hard clay soil exists underneath, you may find that water accumulates in your garden beds quickly. If landscaping edging were not put in place, the water would simply flow outward into your yard, causing another set of problems. However, with landscape edging in place, the water that is not sinking below the surface quickly will simply sit on the surface, threatening plants' well-being above and below the soil.
  
  

Soil Amendment

• A clay soil is usually at the root of any problems of water accumulation that occur as a result of the use of plastic landscape edging. Fortunately, soil can be amended fairly easily. By adding a significant amount of organic matter and sand to your garden bed seasonally, you can ensure that over time you will develop a well draining, healthy soil that will allow water to pass through it rather than collect on top of it. Mulch is a great way to amend your soil over time while creating a clean and well-defined look to your garden bed.
  
  

Plastic Edging as a Solution to Water Problems

• Though it can cause problems as a result of other garden issues, plastic landscape edging is typically used to fix water issues in gardens. By the very act of retaining water in a bed, landscape edging helps to prevent erosion and the loss of topsoil as well as the nutrients held in topsoil within garden beds. Aesthetically this also keeps the lines from garden and lawn from blurring, as erosion will cause topsoil to fall over lawns.