by Sara Williams
Saskatchewan Perennial Society
If you’ve recently purchased a new home, you’re probably anxious to begin landscaping. But before planting, check out your soil. New homes in new developments may or may not include topsoil: it could either have been sold, covered, or moved in the process of grading, developing infrastructure (roads, sewers, etc.) or building the house itself. Even if your ‘new’ home is in a mature neighbourhood, it is still worth the time and effort to evaluate your soil.
The first step is to identify your soil’s texture or the proportion of sand, silt and clay. This can be done through a time-honoured method called “manual texturing”. Simply place a bit of soil in the palm of your hand along with enough water to wet it. Then rub the mixture between your thumb and forefinger.
If it’s gritty and you can feel individual particles, the soil is predominantly sand. If slippery and sticky, it’s predominantly clay. If it’s soapy or silky, it’s predominantly silt. If you can’t figure it out, it’s probably somewhere in between these extremes – and that’s a good thing. A soil that has equal proportions of sand, silt and clay is called “loam” and is the preferred type for most gardening activities. Note: The word “loam” describes soil particle size, not organic matter content.
The next step is to figure out how much, if any, organic matter the soil contains. This is straightforward. Regardless of texture, the darker the colour, the more organic matter is present – and the more the better. Black soils are high in organic matter; grey soils are low.
Step three is determining drainage. Few plants tolerate seasonally or permanently waterlogged soils. Drainage will likely be a problem if your lot is in a low area of a development with other lots draining toward it, or if your subsoil is predominantly clay.
If you find yourself in either of these situations, and water sits for a while in spring or after a heavy rain, there are solutions. You can build “dry stream beds” that act as drainage channels, carrying excess water away from your landscape. These can lead to a back lane or across a front sidewalk into storm sewers. Check with your town or city authorities for information about drainage bylaws.
A second solution is to plant flowers, bulbs, and small shrubs on raised berms so their root systems are not sitting in seasonally standing water. A berm is a mounded planting bed up to 60 cm (2 ft.) in height and 2 to 3 m (6-9 ft.) in width, with sides that slope gently down to the original grade. Besides keeping plants out of waterlogged soil, it makes for a more interesting backyard topography in our flat prairies. When developing a berm, add a generous amount of organic matter so it doesn’t dry out in the prairie wind. Berms that are gently curved to fit the space they occupy are more pleasing than rigidly geometric ones.
Prior to purchasing and spreading topsoil or soil amendments, cultivate the existing soil to a depth of about 15 cm (6 in.). This can be done by hand digging (which is said to build character) or tilling.
It’s critical that this step be carried out to improve drainage. Avoid creating distinct layers of different types of soil. By first loosening the existing soil, it becomes much easier to thoroughly incorporate any topsoil or amendments that are added later. If good quality topsoil is simply dumped on top of poor soil, you’ll find that many plants will root into the first layer, but then tend to root laterally or sideways once they reach the “poor” soil below.
This results in shallowly rooted plants that are vulnerable to environmental stress such as heat, cold, strong winds, drought or flooding. As well, the upper layer (the good soil) will become saturated with rain or irrigation water before any water begins to percolate into the different type of soil texture below. Again, the final result is shallowly rooted plants.
Next week: Purchasing top soil and soil amendments.
Sara Williams is the author and coauthor of many books including Creating the Prairie Xeriscape, Gardening Naturally with Hugh Skinner and, with Bob Bors, the recently published Growing Fruit in Northern Gardens. She continues to give workshops on a wide range of gardening topics throughout the prairies.
This column is provided courtesy of the Saskatchewan Perennial Society (SPS; firstname.lastname@example.org ). Check our website (www.saskperennial.ca) or Facebook page (www.facebook.com/saskperennial) for a list of upcoming gardening events