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Testing Garden Soil: Proven Ways to Get the Best Crops

Man Testing Soil

Are you wondering why you’re having trouble growing plants?  Are your beefsteak tomatoes more like meatballs?  One possible solution could be discovering how to test the garden soil. Once we know the conditions, we can improve the garden soil.

A sad farmer who didn't know how to test soil.
Did the soil harm his plants? He won’t know until he tests it.

Soil Testing:  DIY or Professional?

Professional help is always an option when testing soil for the vegetable garden.  The local cooperative extension office or testing lab will be glad to help.

Testing a soil sample at a lab is the best way to find and correct issues. They’ll give you a full report on the soil test results with recommendations for solving any problems.  To avoid the expense, you can also do many tests yourself.

I’ve used labs several times in my professional career.  They were always valuable partners when trying to solve unknown chemical problems.

But I always test my garden soil at home.  The home tests are simple and fun to do.  I also have an insatiable curiosity, so doing soil tests helps to please that compulsion!

Some of the options mentioned in these articles aren’t one-shot solutions. It may take several times to correct the soil.  It all depends on how bad the problem is.

Let’s “dig into” these interesting soil problems and see what we can do to solve them.

A beautiful harvest of fresh vegetables in a wooden box.
When the soil is healthy, the harvest is healthy.

Soil pH Tests:  Like a “mood ring” for your garden

Testing the pH level is one of the easiest things to do. Many digital soil pH testers and kits that give quick results are available.  Soil pH determines how well roots can absorb nutrients.

The pH test measures whether the soil is alkaline, neutral, or acidic.  Healthy plants prefer neutral pH to slightly acidic soil.  If the soil is too acidic or alkaline, your plant growth will suffer.  That’s what makes the pH test like a mood ring for the soil.

Here are the basics for pH:

  • The pH scale ranges from 0 to 14.
  • Neutral soil has a pH of 7, so that soil is neither alkaline nor acidic.
  • A reading below 7 indicates acidity.
  • A reading above 7 indicates alkalinity.
  • The letters “pH” stand for “power of hydrogen” or “potential of hydrogen.”
  • For acids, pH is the relative amount of free hydrogen ions (H+). For alkalis, it’s the free hydroxyl ions (OH).

You can find the recommended plant pH on the seed packet, in gardening catalogs, books, or online.  Most plants can withstand a pH range from slightly acidic to alkaline.

One exception is blueberries.  They need acidic soil with a pH between 4.5 and 5.5.  Blueberry bushes in any other soil get yellow leaves and have poor production.

A handy Guide to Testing Garden Soil pH is on the Hanna Instruments website.

Besides pH, many soil test kits can test for nutrient levels. These nutrients mainly include nitrogen, phosphorus, and potassium (NPK). Click here if you’d like to see some of the Best Soil Test Kits and Meters.

Video: Testing Garden Soil pH at Home

How to do a Quick-Check for Acidic, Alkaline, or Neutral Soil

You’ll need some vinegar, baking soda, distilled water, and about ½ cup of soil to do these tests. Distilled water is necessary because it won’t affect the test results.

These tests won’t give you the exact pH, but they’ll tell you where it’s pointing.

  • Put a couple of tablespoons of soil in a bowl and add ¼ cup of vinegar.  If you see bubbles, the soil is alkaline.
  • Put a couple of tablespoons of fresh soil in a bowl.  Moisten the soil with distilled water and then sprinkle it with baking soda.  If you see bubbles now, the soil is acidic.
  • If you don’t see any bubbles either way, the soil is neutral.  That would be a definite pH of 7.0.

Video: Raising and Lowering pH Values Based on a Soil Test

How to Correct Soil pH

Soil That’s Too Acidic

Anything that’s too acidic needs an alkaline material to neutralize the acid.  That swings the pH toward the neutral or alkaline side of the scale.  For gardens, the preferred alkaline material is limestone.

The three most popular types of limestone are:

  • Calcitic limestone is calcium carbonate.  This is the limestone that gardeners and farmers use most often.
  • Dolomitic limestone is calcium-magnesium carbonate.  Use this only if your soil also has a magnesium deficiency.  A soil testing service can check this for you.
  • Hydrated lime is calcium hydroxide. It quickly changes the pH, but the effects are short-lived. Handle it with care because it can irritate mucus membranes.

The best to apply lime is in the fall. That will give it time to act on the soil’s pH before the next growing season.  Five pounds of lime per 100 square feet of soil should raise the pH by one point.  This can vary depending on the soil type and the initial pH.

A Personal Story About Lime

I had a bad experience with lime when I was about six years old.  My grandfather kept lime near his garden to dust vegetables like cabbages.  It must have worked to keep the bugs off because he always grew beautiful produce.

My cousin and I were playing near the garden, and he got the brilliant idea to dust my cabbage head with it.  Have you ever had lime in your eyes?  Please don’t do it because it burns like hell.

Mom and my aunts flushed my eyes out with water in time for me to see my cousin disciplined in classic 1958 style.  No harm done; my cousin and I have been close all our lives.

Raising pH With Wood Ash

Another way to raise pH is by using wood ash or grass clippings as a soil amendment.  Wood ash acts faster than limestone since the particles are much smaller.

But you must be careful with wood ash.  It contains about 70% calcium carbonate with potassium, phosphorus, and some trace minerals.

All these things can overlap with organic fertilizers. When they do, they cause severe soil imbalances.  To play it safe, limit applications to 25 pounds for every 1,000 square feet of soil and apply only every 2 or 3 years.

Soil That’s Too Alkaline

One common cause of alkaline soil is using hard water in the garden or raised bed.

You need to add acid to soil that’s too alkaline  If you already have acid-loving plants in the ground, mix two tablespoons of vinegar in a gallon of water.  Watering your plants with this mixture will lower the pH.  Be sure to water at the roots and not on the leaves.

Powdered elemental sulfur is the most common material to use.  Certain soil bacteria use sulfur to create sulfuric acid.  Adding 1 pound of sulfur per 100 square feet will lower the pH by 1 point.  Of course, this will depend on the soil type and the original pH.

Another way to make the soil more acidic is by using ferrous sulfate. It costs more than sulfur, and you need to use eight times more of it. The only positive thing you can say about it is that it acts quicker than sulfur.

Peat moss can also lower pH, but it suffers from excess harvesting.  That can make it too expensive for larger garden plots.

Peat moss is the best choice when you have a few acid-loving plants (like blueberries) or in container gardening.  Organic matter such as shredded leaves would be cheaper.

Good soil with a diagram of the major soil nutrients.

Testing the Nutrient Content in the Soil

Plants are like connoisseurs regarding their soil—they need the perfect balance of nutrients to thrive.  If you want to ensure that your greens have 5-star dining, you’ll need to test the nutrient levels.

The Importance of Nitrogen, Phosphorus, and Potassium (NPK) and Other Nutrients

According to the National Library of Medicine, plants need at least 14 nutrients.  The six macronutrients are:

  • Nitrogen is essential for leaf growth.
  • Phosphorus supports developing roots and flowers.
  • Potassium keeps the overall plant functions running smoothly.
  • Calcium builds cell walls.
  • Magnesium is at the heart of chlorophyll production.
  • Sulfur is a key player in some amino acids and vitamins.

Nitrogen (N), Phosphorus (P), and Potassium (K) are The Big Three for plant nutrition.  The three numbers on a bag of fertilizer (NPK) show the percentages of these nutrients.

Soil micronutrients include:

  • Chloride
  • Boron
  • Iron
  • Manganese
  • Copper
  • Zinc
  • Nickel
  • Molybdenum

Yes, you can have too much of a good thing.  Too much of any of the above soil minerals turns them from nutrients to toxins.

A Note About Chemical Fertilizers

Commercial farms all over the world use chemical fertilizers.  Even home gardeners use them, as evidenced by the vast quantities sold by home improvement and garden centers.

The soil will forgive occasional use, but continuous use comes with a trap.  Here’s what happens:

  • Farmers and gardeners who till the ground use NPK and other chemical fertilizers. Tilling destroys the soil’s structure and biome, killing the life in the soil.
  • With constant tilling, the soil becomes dirt – incapable of supporting life.
  • Chemicals now have to do the jobs once done by living soil.  Plants can’t survive without nutrients.
  • Destroying beneficial fungi and bacteria in the soil makes the plants more susceptible to diseases.
  • To protect against these diseases, farmers have to apply more chemicals.
  • Do you see the endless circle?  Since tilling killed the soil, artificial methods must replace nature’s way.  The solution is to give up tilling and nurture the soil with no-till gardening.
  • Besides destroying the soil, chemical fertilizers and pesticides also pollute groundwater.

Please always use organic fertilizers and pest control.  If your soil has had extensive exposure to chemical fertilizers, see our article about reviving dead soil.

An analog soil testing meter.
A sample of soil in a test tube.

Testing Soil Nutrients at Home

Soil test kits include several chemical tests.  They can be the best option for testing nutrient levels.  Digital meters that feature a “nutrient test” give an overall reading of the nutrient level.

Separate NPK readings require a meter for each nutrient.  Meters with separate readings for each nutrient are also available.  These meters have multiple special probes for each test.

See our page for some of the best soil testing kits and meters. Soil testing doesn’t require heavy digging since you have to collect soil samples only few inches deep.

How to Interpret Nutrient Levels in Test Results

Interpreting nutrient levels can sometimes feel like cracking an ancient code. Here’s a quick guide:

  • If the nitrogen level is low, your plants might show yellowing leaves and stunted growth.
  • Phosphorus is important for healthy roots and flowers.
  • Potassium shortages can result in weak stems and discolored leaves.

Improving your soil isn’t possible until you know what’s in it.  Acting on the soil test results will give you healthy soil and a flourishing garden.

Ready to continue uncovering the mysteries of soil testing?  You can continue with our articles on “Soil Texture” and “Restoring Life to Dead Soil.”

Bob Styer

As a child, I hated gardening. That was mainly because Dad expected us to work in the garden every so often even though we thought play was more important. Over the years, though, I've developed a real appreciation for growing things. Whether you're growing plants for food or to enjoy their beauty, gardening can make your life better. Seize the moment!

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