How to Take a Soil Test

Soil Sampling and Testing

January 29, 2019
Soil Testing

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.