Where to Source Organic Soil
Hello. I'm demolishing a tiny house next door (St Paul) enlarging my yard. I will have quite the large yard now and know I will be doing more gardening with the space. The 15 x 45 foot hole is about 5 feet deep so I will be using some 'fill' but I wonder how deep my garden soil should be, what to use and where to source it. Any suggestions? I am concerned about chemical contaminants such as fertilizer and herbicides if the dirt portion has come from a farm. Tough to know what's in a bulk load of 'garden mix' ordered from one of the local suppliers. Thanks.
Ramsey County Minnesota
Thank you for the question. What an exciting opportunity to expand your gardens! It is great that you are thinking ahead to a proper garden foundation. While we don't recommend specific suppliers for your project, we can provide information so that you can make an informed decision on what resources to use.
Your top layer of garden soil should be about 8-10 inches deep for most typical gardening but depending on what you plant, it might need to be much deeper. Many perennial native plants have roots extending much deeper than the plant is tall.
Please read this excellent publication by Purdue Extension on "Dealing with Landscape Soils" https://ag.purdue.edu/hla/Documents/Mickelbart/other/INLN%202010%2070%202026-28.pdf
We will paste some information from the publication here for you. It is specific to Indiana but the concepts apply for us in Minnesota as well: "Before you purchase topsoil, it is important to visually inspect the soil . . . it’s time for a field trip to the site where the 28 Indiana nursery & Landscape association • www.inla1.org soil is stockpiled! The soil that you select should be free of large stones and foreign materials such as broken glass, paint chips, and plastic. Gravel content should be less than 10%. Ask about any herbicides that may have been applied to the soil source and when. Herbicides have a wide range of active residue time and have the potential to negatively impact plant growth long after the application date. It is important to know that the soil you select is actually that which is loaded and ultimately delivered and unloaded at your site. This comes with developing a relationship with your topsoil supplier. Check the topsoil for plant debris. If there are large pieces of plant material that have not broken down, this may lead to a nitrogen deficiency because microbes that will break down this plant material will take nitrogen from the soil (known as nitrogen immobilization—see the Science Review in this issue). Check for living roots that may be from perennial weeds such as morning glory".
Good luck and thank you for contacting Extension.