Understanding soil health for tree planting

Soil serves as the foundation of your woodlands, supporting trees, plants, fungi and other organisms. In fact, it can be considered an entire ecosystem of its own, as it provides habitat for thousands of species of microbes. These microbes transform nutrients in the soil into a form that is accessible for trees and plants to use, a process essential for tree health and growth. 

Soils vary in their chemical and physical composition across an individual site and the state, and the soil health directly influences the health of trees and the forest as a whole. Like in agricultural settings, understanding the fertility of the soils in your backyard woods and woodlands is important for selecting, planting, and growing trees that will be healthy in the long-term. 

However, soil health is not often as large of a focus in forested settings compared to agricultural settings, where soil testing is a common practice. It can be helpful for small woodland owners to understand the state of their soil prior to tree planting since tree species vary in their preferred pH, nutrient profile, and moisture availability for optimal growth. For example, most trees in northern hardwood communities prefer moist, richer soils, while jack pine can thrive on nutrient-poor, dry, sandy soils.

By learning more about the soil on your land through soil testing and the Web Soil Survey, you can be confident that you have a clear representation of the capacity of your soil to grow healthy trees.  

How to test your soil

The University of Minnesota Soil Testing Laboratory makes it easy to test your soil with step-by-step instructions for sample collection and several available tests, some of which include recommendations for potential fertilizer application. Soil testing may be more feasible for smaller woodlands and backyard woodlots, as the effort required for sample collection increases with the size of the woodland.

Soil sample forms can be printed or picked up from your local Extension office. Soil samples can then be either dropped off in-person at the Soil Testing Laboratory in St. Paul or sent via mail in a sealed container. Detailed guidance for sample collection can be found on the laboratory’s page for lawns and gardens, which includes tree planting. In short, collecting soil samples to submit for testing includes the following steps: 

1. Fill out a soil analysis request sheet for each soil sample. 
2. Take a soil sample to a depth of 12 inches (the recommended sampling depth for trees) using a trowel, auger, spade, or other tool. Make sure to remove grass and litter from the surface of the soil before taking the sample. 
   1. If the sampling area is uniform (terrain is level and there are no expected differences in fertility), take five samples from the area and combine the samples in a bucket, making sure to mix the soil well. Take a pint of soil from the well-mixed composite sample and send it to the Soil Test Laboratory in a spill-proof container. 
   2. If the sample area is not uniform (major differences in condition and fertility across the area), take one sample from each area and keep the samples separate (do not combine the samples). 
3. Label each sample container with your name, address, and sample ID, consisting of 4 numbers or letters of your choosing. 
4. Mail or drop off samples at the Laboratory in a sealed container using the lab's recommended guidance for submitting samples. 

More detailed information on sample collection (including a video), sample submission, and prices can be found on the Soil Testing Laboratory website. All specific questions related to soil testing can be directed to Laboratory staff using the contact information on their website.

Once you receive your soil test report, you can refer to Extension resources for help with interpreting your soil test report. Soil testing reports provide you with valuable information that can help you to select trees that will be best suited for your property.