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Test Your Garden Soil in Fall for Better Spring Growth

Written By: Robin Sweetser Gardener

Test your garden soil this fall for a healthier, more productive garden next year. After the harvest is an ideal time to check your soil’s pH and nutrient levels, giving slow-acting amendments such as lime time to work before spring planting.

Healthy soil is the secret to a thriving garden—but don’t add lime, fertilizer, or other amendments until you know what your soil actually needs. A professional soil test can help you make targeted improvements while avoiding excessive nutrients that may harm plants and pollute waterways.

soil test kit

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.

soil and trowel in a bucket

  • 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.

soil amendments

Decoding the Soil Test Results

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

Nitrogen

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

dung pile

If you are using fresh manure, spread it 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. Ten 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.

Phosphorus

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.

Potassium

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.

Soil

About The Author

Robin Sweetser

Robin Sweetser

Gardener

Robin Sweetser is a longtime gardening writer, editor, and speaker. She and her partner, Tom, have a small greenhouse business, selling plants and cutting flowers and vegetables from their home and lo...

Read more from Robin Sweetser

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Comments

<span>Scott Davis</span> Wed, 06/10/2020 - 10:08
Great article. We had our soils tested by UMass, they were by far the least expensive of all the testing sources we found and are much more accurate than the DIY kits. We live in Vacaville, Ca. where the soils are heavy clay, our area is a former Pecan/Walnut orchard. Temps get to 100 in the day and drop to 65 at night through June so some plants need extra help.
<span>Rononpi</span> Sun, 11/04/2018 - 08:22
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.
<span>Susan Snow</span> Wed, 10/18/2017 - 01:40
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. Thanks! Susan Snow
<a title="View user profile." href="/author/robin-sweetser">Robin Sweetser</a> Wed, 10/25/2017 - 15:15

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.

 <span>Bill Marrs</span> Wed, 10/04/2017 - 12:13
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.
<span>Cecile Robbins</span> Sun, 10/16/2016 - 08:20
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 ??? .
<a title="View user profile." href="/author/robin-sweetser">Robin Sweetser</a> Wed, 10/19/2016 - 17:22

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.

 <span>Kevin Clancy</span> Sat, 10/08/2016 - 21:57
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
<span>Fred</span> Sat, 10/08/2016 - 11:43
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.
<a title="View user profile." href="/author/robin-sweetser">Robin Sweetser</a> Wed, 10/12/2016 - 18:54

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.