In Minnesota, it so often feels like springtime comes slowly, bolts into summer heat then fades into frost just as the tomato plants really get going. But with this year’s warmer El Niño winter, we might have a slightly longer growing season than usual (knock on wood). Take advantage of this to grow your best vegetables yet! You may know that veggies need full sun or partial shade and how much water or space they need. But if the condition of your soil isn’t optimal, you’ll have a much harder time keeping those veggies alive, let alone getting a great harvest. If you’ve had bad luck with certain vegetables in the past (for me, it’s spinach and cucumbers) don’t blame it on your gardening skills just yet. Instead, take a good look at your soil.
Why is soil testing important in Minnesota?
Soil nutrition is especially challenging here in Minnesota. There are multiple soil types and biomes across our state. And many of the vegetables we love did not evolve to grow here (e.g., tomatoes).
Plant life is vast and complex. In the same way that humans need support to survive in certain environments (e.g., tundra, desert, Minnesota) many of our plants need a helping hand. Take time to understand the conditions of your garden soil and amend the soil if needed for the vegetables you’re growing. Consider the three soil questions below when looking for ways to improve your harvest.
1. What soil texture are you working with?
Understanding soil texture is important because it can impact how your plants access nutrients and water. The image below shows the 12 major soil texture classifications (Minnesota Stormwater Manual).
Generally, our MN soil is on a spectrum between sand, silt and clay. Most vegetables want to be in loamy soil (i.e., an even balance of sand, silt and clay). If water often puddles on your soil and then bakes into hard, cracked plates, it’s probably clay. Clay soils are heavy and, in Minnesota, might be slightly red in color. If water drains fast in your garden and the soil looks and feels like sand, it’s likely sandy soil. If your soil is slippery when wet (as opposed to grainy or rocky) it likely contains more silt.
If your soil is on the heavy clay side, adding organic material (like compost) can loosen the texture and allow more air pockets and water flow for your vegetable plants. If your soil is on the sandy side, amending it to include stronger, water-retaining compounds (again, compost) will give your veggies more time to utilize water before it drains away.
Soil texture can also vary from place to place in your garden.
Amending Soil
The most common solution for soil texture problems is adding organic matter. This is why gardeners love compost. Its fluffy texture does wonders for most garden soil, even when it’s not nutrient-rich.
2. Is your soil basic or acidic?
Soil pH impacts how your plants’ roots absorb important nutrients for growth. See the chart below from the Memphis Master Gardeners. The spectrum is represented by numbers, typically 4.0–10.0. Lower numbers are more acidic and higher numbers are more basic. Most common vegetables prefer a soil pH between 6.0 and 7.0.
There are several ways to determine the pH of your soil. You can purchase a soil test kit, try a DIY soil test (try youtube.com for directions on this) or send a sample of your soil to the University of Minnesota Soil Testing Laboratory for testing (instructions are provided online). I do a soil test every few years, and I love how it helps me understand my garden.
Test your soil pH anywhere you plan to grow vegetables since the pH can vary throughout your garden. For example, my soil is a little more alkaline next to the sidewalk and boulevard than it is in other places.
Soil pH is also really important when it comes to growing other plants. Blueberries and azaleas are famous for preferring more acidic soil. This is why they grow so well in our northeastern coniferous biome—lucky you, Duluth!
Managing Soil pH
If your soil is too acidic, you can add lime. Check out Lime Needs in Minnesota. If your soil is too basic, you can acidify it by adding elemental sulfur. Check out Soil Acidification: How to Lower Soil pH. Adding compost is once again helpful here. Most finished composts will have a pH range from 6.0–8.0, pretty near the sweet spot for vegetable plants. (Though it can vary based on what you put in your compost.)
3. How’s your NPK?
If you’ve ever used a fertilizer, you’ve probably seen the “N-P-K” details. “N” stands for Nitrogen, “P” stands for Phosphorus and “K” stands for Potassium, three of the most important macronutrients for plant health.
Testing for NPK on your own is trickier than determining the soil’s pH. You can buy a kit and give it a try—or you can use the same soil test service at the U of M Soil Testing Laboratory. The soil lab’s test results include the NPK levels.
The most common way to add nutrients to your soil is through fertilizers. Use the soil test to choose the N-P-K ratio in the fertilizer that you buy. Another method to amend your soil is strategically planting nitrogen-fixing plants. When you plant pole beans, for example, their roots help add nitrogen to the soil. If you want more phosphorus, several green manure cover crops can add that over time.
Whether your MN soil is sandy or in need of drainage, deficient in important nutrients or not the optimal pH, you have strategies at your disposal to improve the structure of the soil and make it an environment where vegetables can thrive.
Author’s Bio
Brianna Flavin is a Ramsey County Master Gardener intern living on Saint Paul’s east side with her partner and two young children. She’s especially into berry plants and budget-friendly solutions for making small gardens productive, beautiful and beneficial.
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