How to Take a Soil Test

Soil Sampling and Testing

January 29, 2019
Soil Testing


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Do you test your soil? Here’s why it’s worth taking the time to lay the groundwork for a better garden next year.

You don’t have to dig too deeply to discover the secret of great gardening; it is your soil. Without healthy soil it is very difficult to have a successful garden and fall is the best time to evaluate your soil’s health.

Before you start dumping on the lime and fertilizers, your first step should be taking a soil sample to send off for testing. A good soil test will evaluate the basic texture of your soil—and, silt, or clay—and determine its acidity—the pH level. The available amounts of nutrients including magnesium, calcium, phosphorus, and potassium will be calculated and recommendations will be made for raising each to the correct levels for optimum plant growth. Armed with this knowledge, you can make the proper improvements. Too much of a good thing can be just as harmful as too little so let your soil test be your guide.


Where to get a Soil Test

Home test kits are available but they are not as accurate or thorough as professional testing.  Contact your county extension office for soil testing information and instructions. Most have websites; fees for soil testing, along with the proper forms, can be found there. Here’s a list of cooperative extension services by state.

How To Take a Soil Test

  • To take a representative sample, scrape away any surface litter, plant residues, leaves, etc.
  • Avoid sampling in a spot where ashes have been dumped, manure or compost stored, or brush burned.
  • Cut straight into the soil with a shovel or trowel 6 to 8 inches deep making a V-shaped hole.
  • Cut a 1 inch wide slice of soil the length of the hole from one side. Take a 1 inch strip from the center of this slice to use in your sample.


  • Repeat sampling randomly around the garden and mix the samples together in a clean glass jar or bucket. Since we use raised beds we take a slice from each bed and mix them all together.
  • Measure out a cupful of soil, dry it indoors for a few days, and seal in a plastic bag with your information on it.
  • Send it in with the proper forms and fees.


When you get your test results the fertilizer recommendations will be quite specific, and speak to three elements:  nitrogen, phorphorus, and potassium.


N stands for nitrogen which helps plants make leafy growth. For nitrogen they will tell you how much manure to use.


If you are using fresh manure, spread it on in the fall so it can break down over the winter and be safe for spring planting. If you prefer, dried blood, alfalfa, soybean, or cottonseed meals can be substituted. Nitrogen is released quickly from them so it is best to wait until spring to add it to your soil. 10 pounds of blood meal supplies the same amount of nitrogen as 10-20 bushels of manure but without the added benefit of all the organic matter that manure contains.


P stands for phosphorus which is necessary for germination, strong root growth, flowers, and fruit. It helps plants absorb minerals, grow strong stems, and withstand disease. Rock phosphate provides phosphorus, magnesium, and trace minerals. Rock powders are wonderful soil enhancements. They are slow acting but long lasting so they need to be applied only every 3-4 years. Bone meal and bone char are more readily available sources of phosphorus.


K stands for potassium or potash. It regulates the flow of water in plant cells and is necessary for flowering, fruiting, and disease resistance. A lack of potassium will cause plants to have weak stems and stunted growth. For added potassium you can use granite dust or greensand which is made from glauconite, an ocean mineral high in potassium and iron. Wood ashes are also high in potash.

Most gardens have room for improvement. Take the time now for a better garden next year!

See more about NPK Ratios And What This Means.

About This Blog

Get inspired by Robin Sweetser’s backyard gardening tips and tricks. Robin has been a contributor to The Old Farmer’s Almanac and the All-Seasons Garden Guide for many years. She and her partner Tom have a small greenhouse business and also sell plants, cut flowers, and vegetables at their local Farmer’s Market.

2019 Garden Guide

Reader Comments

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Sample Collecting

Thanks so much for your instructions regarding the proper method of collecting soil samples for testing. I am Master Gardener and one of my volunteer activities is performing the soil tests on samples that people bring into our local Extension Service office. All too often, I receive a sample that is mostly mulch or grass. You really need to collect your sample from the root zone which is about 6 to 8 inched below the surface for most garden plants.

Avoiding Genetically Modified Organisms in soil amendments

When I first started gardening in 1970, I amended my soil with blood meal, alfalfa, soybean, or cottonseed meal. But, now, they all contain GMOs thanks to Monsanto. I now use kelp meal, worm castings from red wigglers fed organic produce wastes, and composted leaves, unsprayed grass clippings, and a variety of animal manures from livestock not grown with GMO grains or grasses.

What goes into the soil comes out in food, so I am extremely careful with my supplements.
Can glacial till be used to add minerals OR will it put unwanted heavy metals like chromium 6, arsenic, lead, mercury, and other poisons?

From peer reviewed studies around the world, I'm learning that GMOs include high levels of herbicide and antibiotic resistant bacteria such as
Clostridium botulinum. C. botulism if found at poultry houses, it is also found if dairy livestock in Germany an the source IS animal feed sprayed with Glyphosate resistant herbicides and the pathogenic bacteria to which the feed is resistant. See M.Krueger et al, 2012, 2013, 2014, 2016. This highly resistant bacteria is killing dairy cows, is was found at farms, in farm house dust, and in the feces of the animals, humans, and human children with dire consequences!

Suggestions are wanted on other uncontaminated sources of soil amendments to add beneficial minerals to the soil.


Susan Snow

Glacial till can be naturally

Glacial till can be naturally high in some types of heavy metals, depending on its source. How do you feel about using other kinds of rock powders such as basalt or granite dust? They are good at re-mineralizing soil. The best thing you can do is to be aware of your sources. I always get my soil amendments from a trusted organic company. Check out the blog post on soil amendments for more information.

Growing Soil

Your plants Need 8 Macro-Nutrients and 12-19 Micro-Nutrients (Trace Minerals). The Macro-Ns are - from the air - Carbon (from CO2) and Oxygen (for the roots); The Macro-Ns from the Soil are Nitrogen, Phosphorous, Potassium, Calcium, Magnesium, and Sulphur. Important Micro-Ns are Iron, Manganese, NH3 compounds (Ammonia+), Sodium, Silicon, Zinc, Copper, Boron, and Molybdenum. The ONLY Fertilizers I use are Organic Bone Meal (for Calcium and Phosphorous), 1 year old horse manure, and 2 year old poultry manure. Potting, Planting, and Growing Soil is Always - 35% Silica Sand, 30-50% Humus (from COLD Compost), and 15 to 35% Screened Clay (no rocks) - for the Abundant Trace minerals. Soil pH is Maintained at 6.0 to 6.5 using Only Ferrous Sulfate (which works over 6-12 months). Remember: Hot Composting Produces Fine Mulch - and NO Humus. Bill - Master Gardener - 25 years.

had mode this year

To Ask what to put in the soil about the mod to kill it . I was told to put lime , what to know & DO FOR NEXT YEAR. Thank you ? Cecile & need to know how do you dried out gourd's ??? .

Lime will kill the mold by

Lime will kill the mold by changing the pH of the soil. Too much lime can cause that area to have too high a pH level though and render it unable to grow anything so be cautious when using it to kill mold. As for drying gourds, leave them on the vine until the plants are dead. Let the gourds stay outside in a sunny, well ventilated spot, turn them every few weeks and check for rot. It is okay for them to freeze. It can take months for large gourds to dry.

Soil testing

Thank you for your informative article, readers should also note that the N/Nitrogen P/ Phosphorus & K / potassium can be used in selecting fertilizers at your local gardening stores. All manufacturers use these in the same Symbols in the listings of what is the strength and amount inside everything from lawn,Flower & Veg Fertizers.these can be found on the front of the box and on the back of the bag as well. I think you folks could do all gardeners a great service by writing a detailed article explaining to the consumer how to read and look for these ingredients, to pin point exact needs and buy only what they need . Thanks: K Clancy: Manchester, Nh


Manure is high in nitrogen but it also high in seeds. All kind of weeds and grasses.
These weeds grow much better than the plants you are trying grow.
Unless you can used sterilized manure I don't recommend using it in your garden at all.

The amount of weed seeds in

The amount of weed seeds in manure varies greatly depending on the animal it comes from and their diet. It is amazing what can pass thru their digestive tract unscathed.  It takes really hot composting to render the seeds incapable of germinating. Nitrogen can come from other sources but manure is most beneficial for its high organic matter. Compost can provide organic matter but it also can harbor weed seeds.


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