“Have you done a soil test?” is one of the first questions Extension Master Gardeners ask if you’re starting a new gardening project. Do you know what a soil test can tell you—and what it can’t?
Useful information from soil tests:
- Nutrients your plants need to grow
- Primary macronutrients: Nitrogen (N), Phosphorus (P), and Potassium (K)
- Secondary macronutrients: Calcium (Ca), Magnesium (Mg), and Sulfur (S)
- Minor nutrients: boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc
- Soil acidity level (pH)
Your soil test will tell you the amount and type of fertilizer to use to provide the nutrients your plants need and how to adjust the soil pH to the appropriate level. It can also tell you if you have too much of certain nutrients! Overfertilizing can be as detrimental to your plants’ growth as too little fertilizer.
Your soil test won’t tell you if you have:
- Poorly structured soils
- Plants may have difficulty getting established on sites where topsoil was stripped away, or soil layers were disturbed and/or compacted during construction.
- Heavy clay soils, in particular, are difficult for roots to penetrate.
- Too much or too little soil moisture
- Poorly drained soils may prevent plant roots from getting enough oxygen.
- Drought or fast-draining soils may lead to root damage/death from too little soil moisture.
- Watering too frequently or not deeply enough can create moisture problems for plants in good soils.
- Plant competition
- Shallow tree roots or the roots of plants spaced too closely may compete for soil nutrients.
- Allelopathic plants—such as walnut trees—may act as herbicides and keep nearby plants from thriving.
- Shade from other plants may inhibit growth of sun-lovers.
So, knowing the proper nutrients and soil pH is a start, but having your plants thrive means making sure your soil has appropriate soil structure and moisture, and providing them with appropriate space and plant companions.
Article by Debbie Green Buncombe County Extension Master GardenerSM Volunteer
For more information:
Soil testing in North Carolina:
“What a Soil Test Does Not Tell You” (scroll down to last article in this newsletter):
Allelopathy in walnut trees: