When it comes to successfully growing shrubs, trees, perennials and many other types of plants in the landscape or garden, there's perhaps nothing more important as soil drainage. You can do everything right in terms of after-care, however, if the soil drainage doesn't meet the requirements of a specific type of plant there could be problems. Too much or too little water can cause injury and even death to certain types of plants. Before planting, it's always best to know the soil drainage requirements of any plant or tree.
Types of Soil Drainage
(Scroll below for soil drainage testing instructions)
Before planting any type of plant in your landscape or gardens make sure to know the soil drainage requirements for that type of plant.
There are 7 basic types of soil drainage. of which most mesophytic plants can be grown. What does "mesophytic" mean? Mesophytes are terrestrial plants which are adapted to neither a particularly dry nor particularly wet environment. That being said, mesophytic plants often have specific soil drainage requirements that fall between 3 to 5 in the list of descriptions below. Non-mesophytic plants, such as some types of succulents or aquatic plants will require soil drainage at the extremes; either excessively to somewhat excessively drained to poorly or very poorly drained.
Excessively Drained soil allows water to drain through very rapidly. Excessively drained soils are commonly very coarse textured, rocky, or shallow. Some are steep. Excesively drained soil is free of wetness almost immediately after any amount of rainfall or irrigation.
Somewhat Excessively Drained soil allows water to drain from the soil rapidly. Many somewhat excessively drained soils are sandy and rapidly pervious. Some are shallow. Some are so steep that much of the water they receive is lost as runoff. These soil drain within 6 hours after heavy rain or deep-soaking irrigation.
Well Drained soil allows water to drain from the soil readily. Well drained soils are commonly medium textured and typically hold water for no more than 24 hours after a heavy rain or deep-soaking.
Moderately Drained soil allows water to drain from the soil somewhat slowly during some periods. Moderately well drained soils are wet for only a short times after a heavy rain or deep soaking irrigation. They commonly contain enough organic matter to hold moisture evenly for over a period of 24 to 48 hours after a heavy rain or deep-soaking irrigation.
Somewhat Poorly Drained soil allows water to be removed slowly enough that the soil is wet for significant periods during the growing season. Wetness markedly restricts the growth of many types of plants unless artificial drainage is provided. Somewhat poorly drained soils commonly have a high water table, additional water from seepage, nearly continuous rainfall, or a combination of these. Somewhat poorly drained soil remains soggy or wet for 48 to 72 hours or more after a heavy rainfall.
Poorly Drained soil drains so slowly that the soil is saturated periodically during the growing season or remains wet for long periods. Free water is commonly at or near the surface for long enough during the growing season that most plants, with the exception of bog or aquatic plants, cannot be grown unless the soil is artificially drained. Poor drainage results from a high water table, seepage, nearly continuous rainfall, or a combination of these. Poorly drained soil is almost always saturated, soggy or wet.
Very Poorly Drained soil does not allow water to drain naturally which results in standing pools or bodies of water. These soils rarely if ever dry out, even during periods of drought. Water is removed from the soil so slowly that free water remains at or on the surface during most of the growing season. Unless the soil is artificially drained, most plants, with the exception of aquatic plants, cannot be grown.
How to Test For Soil Drainage
A test I often use to check soil drainage starts by digging a hole 12 by 12 inches square and about 12 to 18 inches deep. After digging the hole fill it with water and let it drain. Then, after it drains, fill it with water again, but this time clock how long it takes to drain. In well-drained soil the water level will go down at a rate of about 1 inch an hour. A faster rate, such as in sandy soil, may signal potentially dry site conditions; a slower rate is a caution that you either need to provide drainage or look for a species tolerant of wet conditions.
Though many plants and trees grow best in a deep, moist, well-drained soil, each plant species has a different level of tolerance to moisture in the soil. Of course, other site factors such as USDA Cold Hardiness Zone, soil pH, soil type and sun exposure are also important considerations.
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