Why Test Soil: Avoiding Toxicity and Maintain Healthy Growing

  • Difficulty Rating: Beginner
Why Test Soil: Avoiding Toxicity and Maintain Healthy Growing

The soil beneath our feet is quite often the most ignored area of the garden. This occurs despite the fact that plants rely on it to grow and thrive.

It is from the soil that plants draw much of the water and nutrients they need to stay healthy and complete the process of creating their own food. If toxins exist in the soil, plants may absorb them. If nutrients are out of balance, plants may fail. And, if soil pH is outside the optimal range, our plants may struggle – even if we provide them with sufficient compost, fertilizers, water and sunlight.

Fertilizer does not actually feed plants. When we amend our soils with compost and other fertilizers, we aren’t actually providing plants with food sources. Instead, these materials are components of the food factories that are plants.


When plant roots encounter the various elemental materials found in garden soils, they absorb some of them, use some in their processes, store some in their roots, and pass on some from their various expiration systems. Because plants may absorb and then store unusable toxins like lead and arsenic, we may end up consuming them when we munch on an innocuous looking carrot or beet.

As well, some nutrients plants need deplete from the soil more rapidly than others. For instance, Nitrogen, which is critical to the green growth of plants, quite often needs to be replenished more often than key nutrients such as Phosphorus, which may build up in the soil. Then, if nutrients build up in excess, they can further inhibit a plant’s ability to draw out others they need. For example, if we have excessive Potassium in our soils, nutrients like Nitrogen and Calcium are blocked from our plants, which can lead to yellowing and blossom end rot in tomatoes. Adding more costly Nitrogen or Calcium to fix the problem won’t help until the imbalance is corrected.

And, making matters even more troublesome is the question of balanced pH in the soil. Most plants perform best when the soil pH is between 6.2 - 6.5. When pH is outside this range, plants can struggle significantly even if nutrient availability is sufficient.

Although soil is very complex and may seem daunting, it is easy and inexpensive to get a handle on it through soil testing. For around $10-$20, a soil lab will evaluate your soil for pH, micro and macro-nutrient status, and toxic element levels. Then they will help you understand how best to amend your soil. If your soil is too acidic, they will suggest type, timing and ratio of lime applications to 'sweeten' the soil for optimal growth. They will suggest which type of fertilizer to apply to provide missing nutrients without adding more of others that you may already have. And, they will provide you the peace of mind that you’re growing food in a space that is lead-free and healthy for you and your children.

To create and maintain healthy garden soil, plants and food crops, consider gathering and sending in some soil samples. It’s a fun project with kids, and it will give you some very powerful knowledge toward being a better, healthier gardener. Plus, you’ll likely save money and improve the environment in the long run by reducing over-applying costly fertilizers!


Here’s how to gather and prepare your home soil samples for testing:

Select a garden bed to test. (Ideally, samples are taken on a bed-by-bed basis rather than from all over the garden. This way, if a problem does show up in the lab, it is easier to isolate a problem area.)

  • Gather a bucket for storing and drying soil and a digging tool like a Big Grip Trowel.
  • Take a few scoops of soil from your chosen bed, digging down about 12-18î into the bed to get a good mixture of soil deeper than just the surface. Mix and spread the soil in your box (gather about a total of 5 cups of soil).
  • Place the bucket of soil somewhere it can remain undisturbed for few days as it dries.
  • Label a sealable bag with your soil sample name, your address, name, and phone number.
  • Give your dried soil a good mix. Then, scoop about 1 cup of the dried soil into your labeled bag. Seal the bag, and mail it to the soil lab of your choosing, following any additional directions they may provide.
  • Within just a few weeks, you should receive a packet in the mail, a tweet or an email advising you on your soil test results and how to adjust your soil for optimal growing results.

There are a number of soil labs providing a range of testing options and prices. Some agricultural extension offices will even provide basic testing for free, but they often don’t provide details on how to adjust the garden based on the facts they find.

Following are a few testing options available in the United States:

Umass Soil Testing: Amherst offers several different tests including a basic soil nutrient and composition test for about $10-15 and a separate texture (% of sand, silt, clay) test for around $50.

  • Midwest Labs: Offers a huge array of testing options from simple nutrient details to nematode levels to nitrate concentrations to much, much more.
  • Woods End Research Lab: Woods End offers a soil test for microbial content levels.
  • Home soil test kits: To get basic pH and/or NPK values, a home kit can be fun. They can also be inaccurate and don’t help you understand what to do with the results.