Laura Stegeman, PHC is the owner of Gardens by Laura. After spending far too many years in the rat race, she came to her senses and obtained the Prairie Horticulture Certificate in Landscaping & Arboriculture from Olds College. Laura now designs, installs, and maintains prairie hardy gardens in Calgary, AB. Visit her website at www.gardensbylaura.com for more details and to follow her blog.
Soil is the foundation of all gardens. This medium is required for providing plants with nutrients and water, as well as physical support. Depending upon your geographic region, soil content varies. Its basic components are mineral, organic matter, and pore space of water and air.
The mineral component in soil are sand, silt, and clay particles. Each particle type has different properties which in turn affect the type of plants that thrive in that soil. The largest particles are sand particles. Sandy soils tend to be porous and loosely packed. This allows water and nutrients to flow through rapidly. As a result, this type of soil is best suited for plants that don’t prefer a moist environment such as succulents. More frequent application of fertilizers are usually required, and soil erosion can be a problem.
Silt are the medium-sized particles found in soil. Water and nutrient flow through this soil type is moderate.
Clay particles are the smallest of the three minerals providing more pore space in the soil. Therefore this soil has the potential for holding the greatest amount of nutrients and water available for plants. On the downside, if this soil becomes compacted, the pore space will not have enough water and air available for the plants resulting in their demise.
Another component of soil is organic matter. This acts as the nutrient storehouse for plants as well as improving the structure of the soil. Nutrients are present in the soil, either from adding fertilizer or naturally occurring predominately in the organic matter phase. As organic matter is decomposed by microorganisms, nutrients are released in a format available for plant utilization. A continuous supply of nutrients becomes available for plants by maintaining a healthy organic matter component in the soil. In addition, the organic matter acts as a glue to hold the mineral particles together into aggregates. This soil structure improves root growth, emergence of seedlings, movement of water and nutrients, and aeration of soil.
About half of the volume of soil is comprised of pore space; equally divided between air and water. When gardens receive too much water the soil becomes water-logged which will displace soil air. The roots cannot respire and the plant may die. Conversely, lack of water results in drought, and if plants reach their permanent wilting point, they will not survive.
Loam is the ideal garden soil which has characteristics of sand, silt, and clay. The preferable mineral portion of loam is 45% sand, 35% silt, and 20% clay. This combination will give your garden the best chance of growing the healthiest and largest variety of plants.
Testing Your Soil:
- Add about one cup of garden soil to a mason jar.
- Add 1 tsp. dish detergent and fill with water. Shake well.
- Let the solution settle for several days. Sand will settle at the bottom; silt in the middle, and clay at the top. The clay layer make take several days to settle.
- Measure each mineral layer and compare to the whole. e.g. if bottom layer is 1/2” deep and the total soil depth is 3”, the soil contains 17% sand.
If you don’t happen to have a garden with an ideal loam soil, work with what you have and utilize plants that thrive in your particular soil type. Gardening books and internet resources will provide you with information regarding what type of soil various plants need. If your garden has sandy soil, don’t choose plants that grow well in clay soil. If you region has high rainfall, don’t select plants that prefer a dry environment.
Finally, the addition of organic matter to your soil will add nutrients and improve structure. Remember that ideal soil contains up to 10% organic matter so more is not necessarily better. By adding a layer of compost to your garden of 2-3”, the compost will serve as a mulch as well. Alternatively, the compost can be tilled into the existing soil as you are preparing your garden beds. Organic matter does decompose with time so your garden will require periodic additions, otherwise it will become depleted.