Understanding Your Soil Test Results: What They Mean and What to Do Next

Garden soil testing is one of the best ways to streamline your fertilizer applications and ensure your plants are getting optimal nutrition. If your plants are showing signs of deficiencies like yellowing leaves or slow growth, your soil test may highlight what’s missing. However, the complex scientific jargon of the test results can be confusing for most gardeners. What do all those numbers, percentages, and abbreviations mean? How can you use test results to properly amend your soil? We’ve got the answers.

Modern soil tests use a combination of laboratory tests to find the pH, organic matter, and plant nutrient levels of many different minerals in your garden beds. Let’s dig into the details of each type of test, how nutrients affect your crops, and what you can do to fix imbalanced soil.

How Do I Read My Test Results?

Reading soil test results does not need to be complicated; you simply need to understand what needs to be increased or decreased. Most analyses include a range from “very low” to “medium or optimal” to “high,” which estimates how much of each nutrient is available in the dirt.

Once you’ve collected garden samples and shipped them to a lab, you should receive a test report that includes information like the pH level, percentage of organic matter, CEC (Cation exchange capacity), and a range of essential plant nutrients such as phosphorus, potassium, calcium, magnesium, and micronutrients. 

The reported levels on each parameter provide insights into the belowground fertility and recommendations for amendments to improve deficiencies or excesses. This guide includes more detail on each parameter in easy-to-understand language.

How to Use Your Test Results in Your Garden

The quickest and easiest way to use your soil test results is to first focus on low nutrient levels or deficiencies. Anything that shows up as deficient should be your primary focus for learning and amending. Take note if a specific test result correlates with plant symptoms you’ve noticed in the garden. 

Use Multipurpose Amendments

Consider the available amendments for short-term and long-term remedies. The Epic Soil Test analysis includes annual instructions at the bottom of the results. This will have specific fertilizer recommendations for different times of year, and some amendments can fix multiple issues at once. 

For example, if your soil lacks calcium and magnesium and is very acidic, you can add dolomitic lime to solve all three issues. Similarly, if your test reveals deficiencies in micronutrients like manganese and zinc, an all-in-one micronutrient amendment like azomite may be your easiest solution.

Be Patient

Once you apply the proper fertilizers, micronutrients, and amendments, wait at least one season before testing again. Soil changes are not always instant, and it can take time for nutrients to become available to your plants.

Excessive Nutrients

If your test results reveal an issue with nutrient toxicity or overdose, you may need to dilute your garden bed soil with native dirt or non-soil matierials. Native dirt is simply the kind that exists in place. Garden soil, potting mixes, and fertilizers all have a much higher nutrient content than native dirt. This makes it a great material for diluting. You can add this to your soil with excessive nutrients to lower the profile and make it more suitable for growing plants.

Non-soil materials like peat moss and coco coir can also be added for dilution, as they contain no nutrient content on their own. Coir may be preferable to peat due to its neutral pH. Peat moss is an excellent filler, but it can add acidity. Therefore it’s important to know your soil’s pH before using coir or peat.

Moreover, you may need to cut back on fertilizing and avoid quick-release synthetic fertilizers. Watering may also be necessary to leach out excessive nutrients. Refer to specific nutrient sections below for guidance. 

What Does a Soil Test Tell You? Test Results Explanation

Soil tests tell you the pH (acidity), percentage of organic matter, cation exchange capacity, and nutrient levels of your garden beds. Because soil is the foundation of your garden, tests are one of the most reliable insights into its health. The results can be used in conjunction with visual observations to figure out what is going on below the ground. 

For example, if your blueberries are growing very slowly and have discolored leaves, the high pH level on your test may explain why. Similarly, if your tomatoes have brown dots on the lower leaves and you’ve ruled out disease issues, a deficiency in phosphorus may show up on your test, indicating that you need to add bone meal or composted manure.

Here is every soil test parameter explained in plain language, including its importance in plant growth and how to remedy improper levels.

pH Level

The ideal pH for garden soil depends on the crops you are growing. Most vegetables prefer a pH close to neutral (6.5 to 7.5), but acid-loving plants like blueberries and azaleas prefer an acidic pH (4.5 to 6.0). Some plants like garlic, asparagus, beans, brassicas, and alfalfa tolerate slightly alkaline soil (7.0 to 8.0), but most plants struggle to grow with a super high pH. 

Soil pH can be confusing because it requires an understanding of chemistry and biology. pH stands for the power of hydrogen and measures the acidity or alkalinity of the soil. The pH level affects every plant nutrient and mineral because some nutrients are not available at ultra-high or low pH values. To make matters more complicated, microorganisms affect how nutrients break down and become available to plants. 

In layman’s terms, all you really need to know is the pH range for your specific crops. Here is a quick reference point:

• Vegetables: pH range between 6.0 to 7.0 is best for most species. 
• Blueberries: 4.5 to 5.5
• Azaleas, Camellias, Rhododendrons: 4.5 to 6.0
• Coniferous Trees (Pine, Spruce, Fir): 5.0 to 6.0
• Broadleaf Trees: 6.5 to 7.0

In soils that are too acidic or too alkaline, you will notice yellowing, browning, stunting, and other visible plant issues. The problems with pH imbalances are mostly related to nutrient availability. Plants cannot properly use certain nutrients when the pH is off, which means they become deficient.

For example, a broccoli plant growing in very acidic soil may look yellow and stunted. This is because the nitrogen gets “locked up” in acidic conditions, and the broccoli plant cannot use the nutrients. Adding agricultural lime (limestone) and eggshells can help raise the pH so the broccoli plants can uptake the nutrients they need.

Percentage Organic Matter (OM)

What is Organic Matter?

Organic matter is the secret sauce to a thriving garden. Sometimes called “humus,” this carbon-rich decayed natural material is what makes healthy soil such a delight to work with. Organic materials include anything that was once living. We can enrich soil by returning dead plant and animal residues right back to the source.

Without organic matter, we could not have most ecosystems on Earth. Wild forests and grasslands naturally develop a thick upper horizon that is loaded with organic matter. For example, you may notice the dense duff of fallen pine needles, cones, wood, and decayed plant leaves on the surface of a forest. This is where the bulk of microbial activity and nutrient cycling happens, and we aim to mimic these natural processes in our gardens.

Interpreting Organic Matter Percentages

The percentage of organic matter (OM) listed on your test can be used as a gauge to determine how “rich” and biologically-active your soil is. A high percentage is a good sign that you’re doing something right, especially if you’re growing vegetables, flowers, and plants that enjoy loamy soil! A lower percentage means your garden may benefit from compost or mulch additions. Issues with compaction, hardpans, poor drainage, and crappy texture can usually be improved by boosting organic matter.

Basically, adding organic matter can fix a lot of problems. This is why compost is the most popular garden amendment! I once had a soil science teacher who would give entire lectures of the complexities of soil biochemistry and problems that farmers face, only to ask the final question, “So what is the answer?” Then, he would proudly proclaim, “The answer is always to add organic matter!” 

This carbon-rich material truly is that powerful! It won’t solve every problem in your garden, but it will tremendously improve overall plant health and crop productivity. Organic matter can be lost through tilling, plowing, and soil disruption, so it needs to be replenished regularly. Use the percentage on your annual test results to track how your garden health improves over the year. 

Cation Exchange Capacity (CEC)

Cation exchange capacity (CEC) is a fancy scientific measurement with simple implications for your garden. Basically, if your CEC is high (11-20+), your soil can hold more nutrients and retain more water. This is great for plants! If your CEC is low (under 10), the soil struggles to retain nutrients and may be prone to leaching. This means your fertilizers go to waste, and your plants may have deficiencies. 

CEC measures how well your soil “holds” onto positively charged minerals like magnesium, calcium, and potassium. These nutrients are cations, which are positively charged minerals. Sandy and poor, degraded soils tend to have lower CEC. Nutrients leach through them very quickly, and the soil has no capacity to hold on to nutrients long enough for plants to absorb them. 

Without diving into complex biochemistry, all you need to know is that a higher CEC (above 11) is better for plants because nutrients stay in the soil instead of leaching out. Add organic matter to boost the cation exchange capacity.

Phosphorus (P)

Phosphorus is the “P” in N-P-K. As one of the most vital plant macronutrients, phosphorus regulates many different plant processes. A plant cannot create energy through photosynthesis without sufficient phosphorus. It will also have trouble growing new shoots, roots, leaves, flowers, and fruits. Fortunately, phosphorus is rarely deficient in gardens because compost and topsoils are naturally rich in this nutrient.

If your soil is lacking phosphorus, you may notice young plants with purplish or dark-reddish leaves. This abnormal coloring usually occurs on older leaves first and progresses upward to the youngest leaves. In severe deficiencies, the leaf tips can turn brown and eventually fall off. Fixing a phosphorus deficiency is as simple as adding bone meal, compost, decomposed manure, or green manures like cover crops. 

On the flip side, excessive phosphorus can be problematic, but there is no need to be alarmed by a high phosphorus level on your test results. Many organic gardeners add a lot of compost, resulting in phosphorus levels around 200 to 300 ppm. Not all phosphorus is available to plants at once because microbes are necessary to mineralize (transform) phosphorus into plant-available forms. 

While compost and manures may be very rich in phosphorus, your plants are not necessarily taking up all of those nutrients at one time. Phosphorus toxicity is fairly rare in gardens, but it can occur when applying synthetic phosphate chemical fertilizers. The simplest way to avoid over-fertilizing with phosphorus is to stick to organic, slow-release fertility like compost.

Potassium (K)

The K of N-P-K is potassium, another vital macronutrient for plants. Plants that lack potassium grow weak, floppy stems and low-quality fruit. This nutrient is also associated with how enzymes, water, and carbohydrates move throughout the plant tissue. Without enough potassium, plants often turn yellow (chloritic) between the leaf veins and their leaf tips begin to curl. Plant growth may slow and fruits may fail to develop.

Potassium is widely available in most garden soils thanks to regular applications of compost and rock-based minerals. In fact, you may notice potassium levels up into the 500 or 1000 ppm range. This is far above the optimal level, but it is not usually problematic because plants are not accessing all of that potassium at once. Potassium has limited mobility, and research shows that plants only access 0.3 to 2.5% of the potassium available at a given time.

Although potassium’s mobility is limited, it becomes more available when the soil is moist but not waterlogged. If your soil is excessively dry or excessively wet, the potassium may not be accessible to your plants. Moderating moisture is key for overall plant health and proper nutrient absorption.

In soils with low organic matter and low cation exchange capacity (CEC), you may also have issues with potassium. This is typically a problem in very sandy soil. The solution is to add compost and sea-based organic fertilizers like kelp and seaweed. Greensand is another mined rock potassium source, but some people avoid it for environmental reasons. Whatever you choose, follow the package instructions to avoid overfertilizing with K. There is usually no need to worry about potassium unless it is exceptionally low.

Calcium (Ca)

Low calcium is a common problem in garden soils. If you see a number under 70% pbs on your test, you may have a lack of calcium that is affecting your plant’s growth. This mobile, positively-charged mineral is less available to plants when the soil is acidic, hard, compacted, and low in organic matter. A low pH is commonly correlated with calcium deficiencies. But you’re probably most familiar with calcium issues in relation to blossom end rot in tomatoes.

Blossom end rot occurs when the “butts” of tomatoes look brown and mushy. This happens because the tomato plants don’t have the water needed to allow calcium uptake and fruit growth. Other symptoms of calcium deficiency include short, bushy, slow-growing plants with malformed leaves and brown spots along the margins of the leaf. 

The quickest solution is to apply a calcium-based organic fertilizer. You may need to raise the pH in acidic soil to make calcium more available. For long-term calcium richness, add crab or lobster shell amendments and composted eggshells.

Magnesium (Mg)

Magnesium deficiency is very noticeable because plant leaves turn yellow between the veins, but the actual leaf veins stay green. This is called interveinal leaf chlorosis, and it is distinctive from any other deficiency. It makes sense that plants turn yellow without sufficient magnesium because magnesium is crucial for the formation of chlorophyll, the green pigment in leaves. Magnesium levels fluctuate closely with soil calcium and potassium, so a deficiency of one of these nutrients is commonly correlated with other deficiencies.

An estimated 90-98% of magnesium is not directly available for plants to uptake. Intriguingly, magnesium-deficient soils have also led to magnesium-deficient humans because modern food crops are often lacking in vital minerals. This means you must ensure proper levels of calcium to yield nutrient-dense food. 

If your test shows low magnesium, you can add compost, dolomitic lime, langbeinite, or trace minerals like azomite. Regular annual applications of compost and mulch ensure sufficient organic matter and microbial activity to break down magnesium into plant-available forms.

Sulfur (S)

Sulfur is another micronutrient crucial to protein synthesis and photosynthesis. Without sulfur, plants cannot produce chlorophyll, and struggle to metabolize nitrogen for proper growth. Soil microorganisms also need sulfur in order to “fix” nitrogen in the soil. So, if your beans and peas don’t have enough sulfur, their root-dwelling bacterial allies may not be able to mineralize nitrogen.

The main symptom of sulfur deficiency is chlorosis. Yellowing lower leaves are a key sign of nitrogen deficiency, but sulfur-deficient plants will turn yellow on the upper new leaves first. The quickest remedy is compost or langbeinite application. You can use gypsum (calcium sulfate).

You can typically smell sulfur in allium crops like garlic or onions, as well as the rotting smell of eggs and some compost. Sulfurous compounds are important in healthy amounts but can be toxic if they are applied in large quantities. In fact, concentrated sulfur-based products are often used as organic fungicides to kill plant diseases.

Zinc (Zn)

Zinc toxicity and deficiency are fairly rare, so you don’t have to worry too much about this number on your test. This micronutrient is only needed in small quantities, but it is essential for plant formation of chlorophyll and hormones. There is some evidence that zinc also aids in cold tolerance.

Adding organic matter is the best way to improve zinc levels. Sandy or acidic soils with low organic matter most often have issues with zinc availability to plants.

Manganese (Mn)

Manganese is a lesser-known plant micronutrient that is only needed in small amounts but is still essential to regular plant growth and functioning. Manganese deficiency is often confused with iron deficiency, or it occurs simultaneously. The symptoms are usually yellowing leaves between the green veins of younger plants. Sometimes, necrotic brown spots occur on older leaves. 

If your soil is very alkaline (high pH) or super sandy, you may deal with manganese deficiency. Low soil test results can be remedied by applying micronutrients like azomite or langbeinite. Many organic liquid manganese fertilizers are also available.

In very acidic soils, you may need to raise the pH with dolomite lime to remedy manganese toxicity.

Iron (Fe)

We commonly associate iron deficiency with anemia in humans, leading to weakness and pale or yellowish skin. Interestingly, in plants, a lack of iron can have the same effects. Iron deficiency causes yellow chlorotic leaves and slow or stunted growth. Plants need iron to form chloroplasts and properly carry out photosynthesis. When there is not enough iron, they struggle to grow healthy leaves.

Tropical red-toned soils tend to have plenty of iron, but heavy-clay soils in cold areas usually have low iron. Generally, soil with low organic matter has low iron. You can amend with compost, manure, blood meal, or a chelated iron fertilizer.

Copper (Cu)

Copper issues are not common, so you shouldn’t have to worry about this micronutrient. If you regularly apply manure-based compost and micronutrients, your soil is likely just fine!

Remediation may be necessary if copper shows up in extremely high amounts. Copper toxicity is a major issue in agriculture, where municipal wastes (sewage sludge) and copper-containing pesticides are applied. Avoid these products and contact your local extension agency for advice. You may need to grow in raised beds or containers to avoid contaminated soil.

Boron (B)

The final plant micronutrient on your test is boron. Scientists find that boron deficiency is the most widespread plant deficiency in crops around the world. Plants without enough boron will drop their leaves and fail to produce healthy flowers or fruits. If your soil lacks organic matter, this can be a major issue. 

Fortunately, you can supplement with a complete micronutrient fertilizer like azomite or add boron fertilizer like Borax, but be very careful as adding too much to the soil can cause big problems. Regular applications of compost ensure complete micronutrition. Boron deficiency symptoms usually show up when it is too late, so you may have to wait until next season to fully remedy the issue.

Why Isn’t Nitrogen on My Soil Test?

With all these analyses and nutrient levels, you may be wondering: Where is nitrogen? Nitrogen does not show up on soil tests because the nutrient is highly mobile and changes rapidly in the soil. There are too many temperature, chemical, and biological factors affecting nitrogen availability. 

Soil microbes are the “middlemen” mediators of nitrogen availability to plants. They are constantly breaking down nitrogen and transforming it into different forms. A test cannot tell you the amount of nitrogen in your soil because the levels change rapidly. 

The best way to ensure proper nitrogen levels is to observe your plants and notice if they look pale or yellow. Slow growth is another common sign of nitrogen deficiency. Annually amend with slow-release organic nitrogen sources like feather meal, chicken manure, blood meal, seaweed, alfalfa meal, or compost.