Talking Plants

Jillian Patrie | University of Minnesota Yard and Garden Extension

Planting season is right around the corner and many gardeners are gearing up.  Whether you are starting seeds indoors, direct seeding, growing in containers, raised beds or in the ground, there are a few things to keep in mind about soil health.
Testing the soil in a new and/or current garden area is an easy way to understand how the soil supports plant growth.  It is especially important for new garden areas and those that have had issues with plant health.  Soil tests can be done through the University of Minnesota soil testing lab, and will describe soil type, pH, organic matter, phosphorus and potassium levels.  Tests can also collect information about lead, soluble salts and micronutrients, for an additional fee.  Recommendations for amendments are provided with the result which can be forwarded to local county educators for further assistance.  Having a base understanding of soil supporting the plants in your landscape will guide fertilization, plant choice and overall decisions on how the space can be best utilized.  Fargo-Moorhead soil tests will generally report a pH between 7.5-8.5, which is on the basic side, meaning acid loving plants such as blueberries, azalea (rhododendron), blue hydrangea and many others will have nutrient issues in most cases.  Clay soil combined with high pH can also cause soil nutrients to become unavailable to certain plants.  Iron Chlorosis is caused by this combination in the FM area, causing yellowing leaves on maple trees (silver and/or red), apple trees, birch trees, spirea shrubs and many others.  High pH water can also cause issues in annual flowers too, petunias are most susceptible to iron chlorosis.  Fertilizing can remedy this issue in annual beds, and containers are commonly planted using a peat moss based potting soil, which has a neutral or slightly acidic pH.  In the case of trees that are experiencing iron deficiency, chelated iron supplements are commonly used or selecting plants that are less susceptible to iron chlorosis.
Potting soils are generally soilless, meaning they do not contain any traditional soil components.  Peat moss, coco coir, bark chips, vermiculite and perlite are standard ingredients in seedling and potting mixes.  These types of bagged mixes are best for containers, raised bed gardens (with a bottom) starting seeds and houseplants.  Peat moss and coco coir are great for retaining moisture and perlite offers extra help with air and water movement.  Garden and raised bed soil mixes will have a combination of the previously mentioned ingredients along with compost and/or a loam type soil mixture (sand/silt).  This type of soil mix is generally a bit heavier and is best for raised bed gardens that have open bottoms or are deep, as well as being used as an addition to native soil garden plots.  Heavier soils can become compact in containers, causing issues with air and water movement.  This is especially common when heavy garden soil is used in decorative pots, as there is usually less activity from worms and other soil microbes that create good air and water movement.  When selecting a bagged soil mix choose the right soil mix based on the application (containers, in the ground or raised beds).  Many bagged mixes come with added fertilizer, however in container situations this is not to be used as the only source of plant food.  Containers may need to be fertilized each time they are watered.  Moisture control soil mixes are available for most garden applications as well; however this technology should not be used as a means to plant and forget.  Containers and hanging baskets should be checked regularly for watering needs.  The type of plant, size of container and plants in the container and weather conditions all play a part in good watering habits.
***100% coco coir has caused poor seed germination in some vegetable plants.  Use a mix with both coco coir and peat moss to avoid potential issues.
Soil health is an important step for plant health!  For more information about soil and soil testing visit extension.umn.edu.
For questions about this article or local assistance please contact Clay County Extension Educator Jill Patrie at 218-299-7338 or by email at patri350@umn.edu.