The more I garden, the more in awe I am of the soil that helps it grow.
This is a great time of year to dig into- yes even under the snow- and get a soil sample. You’ll be digging up a better understanding how to help your garden grow!
A deeper understanding of the earth that grows our food leads to a deeper respect for it. And I believe the earth could use a little more respect right now!
There are two main options out there for soil testing. Home tests and Laboratory Testing Services. Both of the soil tests check for the basics: Nitrogen, Phosphorus, Potassium/Potash and Soil pH levels. From there things diverge. Let’s take a look at which test might be right for you.
The Home Test
For years my kids have looked forward to doing the home version of testing our soil in early spring, mostly because they get to be ‘soil scientists’ 😊. Letting them dig up the dirt and pour it and the chemicals into the ‘chemistry tubes’ went a long way to getting my kids into gardening. We bought a version just like This One which cost $15 and has lasted three years.
The simple DIY way of buying a soil test kit will only ever give you limited results, maybe telling you if anything is WAY off.
PS: they also sell slick digital soil pH testers if that’s what you really care about.
Laboratory Soil Test
The U of MN, through CFANS, College of Food, Agriculture and Natural Resource Sciences, has a simple online test submission process, and **if you get in before the rush** a quick two week turn-around time. Use the Lawn & Garden form, I checked for “Vegetable Garden”.
Most University/ extension services provide a few different levels of testing, and recommendations. If you plan on planting near a road that gets lots of winter salt plowed up on it, you can check for the “soluble salts test” and you can even test for lead if suspected. They have all the instructions and options laid out on their
online forms. The basic soil test costs $21, soluble salts test costs $9, and lead costs $22 (updated 2025).
I recommend taking two or more samples from different parts of the yard, front and back gardens for example, to compare different growing spaces spots in your yard.
Soil Science Notes
Disclaimer: Soil is unfathomably intricate and in constant flux. So, starting to understand it can seem daunting.
For example, “there are at minimum 1 billion microbes and yards of fungal strands in a teaspoon of average soil”.
Yup, daunting.
But, like with all things worth understanding in the garden and in life; when we take small steps, we can eventually cover a lot of ground. You’ll soon ‘get it’ enough to make a real difference in our gardens, and on our plates – and quite honestly, the world.
Soil is where our food starts, and the soil in use for commercial farming is simply not growing food as well as it used to. We now understand that we’ve been poisoning it plus the animals that eat the food grown this way- from microscopic to the noticeable insects, the birds that eat them… and all the way up to us humans.
Understanding a little about soil science helps you sort fact from fiction. You’ll be able to sniff out the false advertising proposing your purchase fertilizers, pesticides and herbicides. My hope is this overview will get more people comfortable growing 100% organic!
The Soil Nutrients
Plants need lots of things to grow well, but we can boil it down to three basic necessities: Sunlight, Water, Nutrients – let’s dive into those nutrients! Think of soil as the stomach of the plant can help when thinking about taking up these nutrients.
Most soil tests look at amounts of a few very specific chemical nutrients. These results simply can’t take into account the vast soil food web relationships that are required to be in decent proportion for plants to able to access the minerals and nutrients in the soil. But they give us a place to start, a foothold. The elements that are most often looked at are N-P-K; nitrogen, phosphorus and potassium/potash.
N- Nitrogen
Nitrogen gets a lot of press, so I bet you know a fair share about this chemical powerhouse. All plants need nitrogen to make amino acids, proteins and DNA. Nitrogen is also a big component of chlorophyll production and photosynthesis. Plants obtain nitrogen through when bacteria in the soil convert the nitrogen to ammonium and nitrate, which is then taken up by the plants by a process of nitrogen fixation.
The Organic Way to Add more Nitrogen:
Composted manure, Blood Meal, fish emulsion or Worm Castings.
P – Phosphorus
Phosphorus is a vital component of ATP (get your HS chemistry class hats on) which is the ‘energy unit’ of plants. Without enough P, plant stems are usually weak and leaves can turn a blueish-green tint. P is needed right after germination to help lift the plant out of the ground.
Seeds need a reserve of P to accomplish this, so there needs to be enough P throughout the lifecycle of a plant for the seed to hold enough to grow on in its next generation.
The Organic Way to Add more Phosphorus:
with bone meal or kelp meal
K- Potassium/Potash
Potash is a potassium-based product that is often bonded to other chemicals. Plants use most of their available potash for keeping water levels up in their plant cells, and so is added to fertilizers to help with water retention. Plants also use K to activate protein and sugar synthesis, which is basically how plants grow. Often adding
You know how bananas are a good source of potassium- well, only if they grow in soil with available potassium…in the form of potash stored in the soil in various salt forms- from nitrates, sulfates etc- which have gotten a bad wrap as of late- but with all things it’s the form of thing that matters… and these little nutrients are important for all kinds of veggies.
The Organic Way to Add More Potassium/ Potash:
wood ash (slightly raises pH levels), green sand
pH – Acidic to Alkaline
I think this is one of the most anti-intuitive readings out there (anyone else?!). I always have to remind myself that the numbers mean the opposite of what I think. A lower pH level means the soil is more acidic (good for blueberries, those blue hydrangea) and higher pH means the soil is more alkaline (also called ‘sweet’ soil). A pH level of 6.5 is considered ideal for most vegetables, but anything between 6 and 7 will grow good food.
Soil acidity levels have huge impacts on what nutrients are bio-available in the soil. So (and this is another one of those amazing relationships in our soil) even though you have lots of Phosphors in your soil, if your pH is below 6.5 your plants could have trouble absorbing it.
My Soil Test Report
I had two tests done, because I wanted to compare my front yard soil with my vegetable garden soil. We haven’t done anything to our front yard except mow (leaving the mulched grass clippings in place) and throw some fertilizer on a few years back. In comparison, I’ve been amending our backyard vegetable garden soil for years, adding our own compost, leaf mold and building a few “lasagna garden beds” (Read more about No Dig Gardening HERE).
I was curious if all my work was paying off…
Well, it has!
The biggest difference was the % of organic matter. Only 2.8% in the front yard, compared to 9.8% in the veggie patch! Wow! I’m impressed.
Nutrients in higher % organic matter soils (like compost) don’t wash away. They stay put, as long as the soil is relatively undisturbed, another reason I’m a proponent of No Dig Gardening!
The organic matter helps keeps ‘on tap’ more of the nutrients rather than spraying them on only to get washed away.
My pH varied greatly between my front and backyard spaces as well. A pH of 6.0 in the front yard, compared to 7.1 in the back. With just over a 7.0 reading, the Iron and Manganese in my soil might be a little harder for my veggie plants to absorb in the back, which is why I’m looking into adding some more Humic acid to my veggie beds. This is a good article that goes over the basics and drills down about Humic acid (even covers the electronegativity factor).
The report also goes over the levels of Phosphorus and Potassium. But even though Nitrogen is a major building block, it is not included in the Regular Test package because “correlations between the soil nitrate test and plant growth have only been established in some areas of Minnesota, and only for a limited number of crops. One reason for the difficulty in establishing uniform fertilizer recommendations based upon soil test nitrate is that nitrate is easily leached out of the soil by rain-water and so precipitation can significantly change the nitrate test result,” states the U of MN Soil testing laboratory.
I feel like I’m one step closer to digging in to the garden season armed with my soil test results! And what really matters is how we use this information to help grow good food for ourselves and our families. A deeper understanding of the earth that grows our food leads to a deeper respect for it. And I believe the earth could use a little more respect right now!
Congratulations to making it through this science heavy article- you deserve a high five! If you want to dig a little deeper, Dr. Elaine Ingham is one of the most respected soil scientists and was recently interviewed by Joe L’ampl on his Jo Gardener Show podcast, worth every second!
So go ahead and test your soil this season- whichever way you chose your eyes will be opened to some of the life that is being lived just under the surface that helps feed you every day!
Can’t wait to dig in!
Michelle
