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Garden Advice

Getting a Soil Test

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Soil tests are a simple and accurate way to learn more about your garden soil and determine what amendments it needs. A detailed soil test, a little research, and an understanding of the results can drastically improve your yields and eliminate recurring issues in your garden.

Where to Get Soil Tested?

There are a few ways you can get a soil test. While you may find simple home test kits at your local hardware store, these generally aren’t as accurate or detailed as a professional test. 

Typically, you can get your soil tested through your county extension agency or agricultural college. Many extension agencies and state colleges offer residents free or cheap soil testing. They typically include some recommendations if amendments are needed. Private labs also provide these services, but they may not be as affordable for home gardeners as the other options.

How to Find Your County Extension

To find your county extension agency try browsing the listings of Pick Your Own. They list contact information for county extension agencies across the United States.

When to Sample

We recommend having your garden soil tested every one to two years. Orchard areas typically only need to be tested every three years.

Late summer and fall are ideal times to collect soil samples. This time of year will represent how the soil’s nutrient status affects crops. If needed, you can take soil samples in spring, but you should avoid collecting frozen or waterlogged samples as they may not mix well.

Don’t collect soil after adding lime or other amendments. It’s best to wait several months or even longer if the weather is dry until they’ve dispersed into the soil.

Depending on the lab you’re working with, and how busy they are, it may take several weeks to get the results from your sample. It’s best to send them in well before you need the results.

Where to Sample

You want to get a good picture of the soil throughout your garden, not just in one spot. To do this, you’ll create a composite sample to send in, made from samples taken throughout the garden. For small-scale home gardens, five to eight samples are generally adequate. 

If your garden appears to have distinct slopes and soil types, be sure to get a sample from each area. Avoid taking samples from sites that don’t represent your garden well. These may include garden edges and unique wet spots.

How to Take a Soil Sample

Take soil samples using a spade or auger and collect them in a clean container. How deep you should sample depends on your garden type. Aim for small uniform cores or thin slices starting at the soil surface. 

For traditional backyard gardens, sample to the tillage depth. For no-till gardens, take one sample from the top 1 inch of soil and then take a second sample from the same spot at a depth of one to six inches.

For areas you’d like to establish an orchard, take a surface sample from zero to six inches deep and a subsoil sample from six to twelve inches deep. In established orchards, scrape aside plants and organic matter and take a surface sample. 

Once you’ve collected your samples, gently crush them and remove any stones and roots. Then allow your soil sample to air dry. Spread it out on a clean surface in a shady spot and make sure it dries before mailing. Don’t heat your soil to dry it.

Your samples should be at least one cup of soil in a plastic bag. Depending on the agency or lab, they may have you use or provide a specific bag. Follow your extension agency or lab’s instructions for sending your sample. Be sure to include all necessary paperwork and your name and address. 

 

The gardening science can sometimes feel intimidating, but it doesn’t have to! Getting your soil tested is a simple way to learn how to amend and improve your soil correctly. Your soil test and advice from the local extension agency can help you build healthy soil and grow healthier, more productive plants.



Garden Advice

Understanding Soil Tests

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If you’ve never had your soil tested you may want to consider it. While soil tests may seem like something more suited to commercial growers than backyard gardeners they’re actually quite simple and affordable. In fact some local extension agencies and/or state colleges offer this service for free. While you can purchase at home soil tests generally having it professionally done is a good place to start. 

Here’s what you can expect from a soil a test and what it will mean for your garden. 

Macronutrients

Primary Nutrients

The following three nutrients are considered the primary nutrients and the probably the most discussed by gardeners.

  • Nitrogen 
  • Phosphorus 
  • Potassium 

Nitrogen is important for plant’s vegetative growth. Phosphorus helps in root and flower development. Potassium promotes vigor. These are found in a variety of commercial fertilizers and homemade garden amendments.

Secondary Nutrients

  • Sulfur 
  • Magnesium
  • Calcium

Calcium helps plants build strong cell walls, magnesium is an important part of chlorophyll, and sulfur is important for the growth of roots and seeds. Just like primary nutrients these secondary nutrients can be purchased in commercial amendments or you can make homemade ones.

Micronutrients/Trace Minerals

Some soil tests will give you the option of testing for micronutrients or trace minerals. These are minerals that plants need in very small amounts. 

  • Boron 
  • Chlorine
  • Copper
  • Iron
  • Manganese
  • Molybdenum
  • Zinc

Unless you suspect a problem testing for these is probably unnecessary. Most soils have enough to keep plants healthy and deficiencies in these minerals aren’t caused by their lack of presence in the soil rather an inability for plants to take up the nutrient because of other problems such as drought stress or incorrect pH. 

These minerals are also typically present in large enough quantities for gardens in any organic fertilizer or other amendments even simple, good quality compost. 

Soil pH Level

Another important part of your soil test is your soil’s pH. pH is the measure of how acidic or alkaline your soil is. It’s an important feature on your soil test as it affects soil nutrient availability and microbe activity. This means that even if a nutrient is in your soil it may still be unavailable to plants do to your soil’s pH.

It’s also worth noting that some crops like blueberries and potatoes prefer more acidic soil than others. 

Amending Your Soil

Once you get your results you can amend your soil as needed. There are a variety of products available commercially or you can use homemade garden amendments like compost and compost tea, manure, coffee grounds, egg shells, pine needles and more. 

You may be able to get personalized recommendations from your local extension agency or soil testing service.

When adding any garden amendment it’s important to thoroughly research its effects on your garden. Certain amendments like oyster shells for calcium can affect your soil’s pH and may affect the availability of other important nutrients. You also want to avoid adding too much of anything to your garden as this can be just as bad as too little. Excess nutrients can also run off into streams and other water bodies causing toxic algae blooms.

11 Free Organic Methods to Add Nutrients to Your Garden

Seedlings

If you start your own transplants at home don’t forget about the nutrients they need. Buying or mixing a good quality potting mix is important to their success. One of my favorite ways to give seedlings a quick boost is to add a bit of compost tea or liquid kelp to their water. I typically use about 5 TBS per gallon of water. 

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