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

You know soil testing is important, but what do the results actually mean for your garden? In this article, soil expert and former organic farmer Logan Hailey demystifies soil test results in plain language and explains how to use your recommendations for healthier garden soil.

A test tube filled with soil stands against a backdrop of moist, rich, dark brown soil, while a hand holds a handful of soil, emphasizing the examination and analysis of soil properties.


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?

Close-up of a man with a handful of fresh soil and a tablet against a blurred garden background.
Understanding soil tests simplifies nutrient adjustments for optimal growth.

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

Close-up of soil covered with small round gray granular fertilizers in a sunny garden.
Amend strategically for both short-term and long-term benefits.

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

Close-up of a girl in jeans and a checkered green shirt checking the soil in a field.
Allow one season for soil amendments to take effect.

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

View of a compost heap nestled within a DIY wooden bin, accompanied by a garden fork, with a small bird perched atop the bin.
Dilute soil and reduce fertilizing to address nutrient toxicity.

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

Different crops thrive in specific pH ranges.

  • What is It? pH describes the acidity or alkalinity of the soil on a scale from 0 to 14, with 7 being neutral.
  • Importance: The soil pH directly impacts nutrient availability to plants and microbial activity.
  • Too High: A high pH (above 7.5) is considered alkaline and may lead to unavailable nutrients and slow plant growth.
  • Ideal: Most garden vegetables and ornamentals thrive in soil pH from 6.5 to 7.5, but acid-loving shrubs and coniferous trees require more acidic soil
  • Too Low: A low pH (below 6.5) is acidic, which can be beneficial for acid-loving plants but detrimental to many crops, causing nutrient deficiencies and toxicities.
  • Recommended Amendments: Add lime to raise pH (make it more alkaline) or add sulfur to lower pH (make it more acidic). The best time to fix pH issues is at the beginning of the season— use the product recommendations at the bottom of your soil analysis.

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. 

This quick guide makes it easy to understand these numbers: 

  • High pH = above 7.0 = alkaline = add sulfur if you need to lower the pH
  • Neutral = 7.0
  • Low pH = below 7.0 = acidic = add agricultural lime if you need to raise the 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.

Pro Tip: If you are growing a wide diversity of plants, send in separate soil samples for different beds. For example, your blueberry and rhododendron beds should be tested separately from your vegetable and flower beds.

Percentage Organic Matter (OM)

Close-up of a gardener's hand in a black glove holding a garden trowel full of compost with worms on a blurred garden background.
Organic matter enriches soil, boosting plant health and growth.

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

  • What is It? Organic matter (OM) content describes the percent of your soil that is made up of decomposed plant and animal “humus,” or carbon-rich material.
  • Importance: Organic matter improves microbial activity, water drainage, water retention, and the soil’s overall loamy texture.
  • Too High: Most garden soils lack organic matter, so an ultra-high level above 10% is uncommon. Peat bogs are 50-70% organic matter, and few plants grow in pure peat. Soil with too much manure may pose issues with phosphorus toxicity.
  • Ideal: The target garden range is 5-7%, but generally more is better for organic growers.
  • Too Low: An organic matter percentage below 2% is not great for most gardeners, as it indicates poor soil health, low fertility, and problems with soil structure.
  • Recommended Amendments: Compost is the most common and widely available, but deciduous leaves, straw, manure, and plant residues are excellent sources of OM as well.

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.

Organic matter benefits plants by:

  • Boosting microbial activity and supporting the soil microbiome
  • Improving water drainage through the soil profile
  • Ensuring water infiltration (to reduce puddling on the surface)
  • Boosting overall fertility
  • Adding vital plant-available nutrients and minerals
  • Raising the cation exchange capacity (CEC) to reduce nutrient leaching
  • Reducing waterlogging (less risk of root rot)
  • Improving aeration and oxygenation in the root zone
  • Improving water holding capacity (the soil dries out slower)
  • Improving overall soil structure
  • Reducing erosion

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)

Close-up of a woman's hands holding fresh, loose, light brown soil.
High CEC helps soil retain nutrients, benefiting plant growth.

  • What is It? CEC explains your soil’s capacity to retain nutrients and how prone it is to leaching.
  • Importance: If your soil does not retain and exchange nutrients, plants won’t have a chance to absorb them. Low CEC soils are vulnerable to nutrient loss from leaching.
  • Too High: Generally, a high CEC (17-30) means soil is highly productive and healthy. It is very rare for garden soils to reach a CEC that is too high.
  • Ideal: An optimal range for garden soils is 11-16, and CEC generally increases with organic matter.
  • Too Low: CEC below 10 is considered poor soil and may struggle to hold onto plant nutrients.
  • Recommended Amendments: Adding organic matter is the best way to improve 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)

The soil compost teems with rich, dark earth interlaced with decomposing organic matter, punctuated by the wriggling presence of earthworms.
This nutrient is essential for photosynthesis and overall plant growth.

  • What is It? Phosphorus is a plant macronutrient mineralized by soil organisms through decomposition processes.
  • Importance: Phosphorus is essential for plant root development, flowering, and fruit production.
  • Too High: Excessive phosphorus (over 400 ppm), especially in high pH soils, makes it difficult for plants to uptake zinc and iron.
  • Ideal: The ideal range is 42-68 ppm, but compost-rich organic garden soils tend to be higher.
  • Too Low: Phosphorus deficiencies reduce shoot growth and may lead to purple or reddish leaves, especially on the leaf edges.
  • Recommended Amendments: Compost, animal manure, and green manure (plant residues) are the best sources of phosphorus.

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)

Close-up of a large garden shovel full of wood ash on a garden bed.
Vital for strong plants, lush foliage, and fruit quality.

  • What is It? This plant macronutrient occurs naturally in rocks, wood ash, and seaweed products like kelp. It occurs in smaller concentrations in compost and organic materials.
  • Importance: Potassium is crucial for strong stems, quality fruit, and plant disease resistance.
  • Too High: Excessive potassium blocks plants from absorbing magnesium and calcium.
  • Ideal: The optimal K range is 124-152 ppm, but many organic gardens exceed 500 or even 1,000. Ppm stands for “parts per million” and is a common unit of measurement for soil nutrients.
  • Too Low: Potassium deficiencies lead to weak stems, low-quality fruits, and susceptibility to diseases. You will notice yellowing at leaf tips and between leaf veins.
  • Recommended Amendments: Potassium is quickly available in dried or liquid kelp and seaweed fertilizers, as well as greensand or wood ash (potash).

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)

Close-up of soil sprinkled with broken eggshells to enrich it with calcium.
Ensure robust growth by addressing calcium deficiencies in soil.

  • What is It? Calcium is a plant micronutrient mineral that mostly comes from weathered rocks.
  • Importance: Plants need calcium to form their cell walls, develop roots, and uptake other nutrients.
  • Too High: Excessive calcium is rare, but it could hinder uptake of other plant nutrients.
  • Ideal: The recommended range for calcium is 70-85% pbs. Pbs stands for “percent base saturation” and is a measurement of calcium availability in soil.
  • Too Low: Calcium deficiency (under 70% pbs) most infamously causes blossom end rot in tomatoes. It can also cause poor root growth and distorted leaves.
  • Recommended Amendments: Crab and lobster shells, calcium nitrate, and baking soda are popular organic amendments to improve soil calcium. Foliar products tend to work the quickest to remedy calcium deficiencies.

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)

Close-up of pebbles of different shapes and sizes across the entire surface of the soil illuminated by the sun.
Combat interveinal leaf chlorosis with magnesium-rich amendments.

  • What is It? Soil magnesium is a mineral that originates from silicate rocks.
  • Importance: Plants need proper magnesium to produce chlorophyll, the green pigment in leaves necessary for photosynthesis. Magnesium also ensures overall healthy growth.
  • Too High: It is rare for garden soils to have excessive levels of magnesium unless you add a lot of limestone.
  • Ideal: The optimal magnesium range is 15.1-25% pbs (percent base saturation).
  • Too Low: Low magnesium typically manifests as yellow leaves, especially between the leaf veins. It is commonly correlated with acidic, sandy soil.
  • Recommended Amendments: Dolomite lime raises soil pH and boosts magnesium. If you want to add magnesium without changing the pH, consider azomite or langbeinite. 

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)

Close-up of water spraying young kale seedlings growing in soil covered with straw mulch.
Ensure proper growth with sulfur for chlorophyll and nitrogen metabolism.

  • What is It? Sulfur is a plant micronutrient that commonly comes from organic materials.
  • Importance: Sulfur is essential for enzymes, proteins, chlorophyll, and plant uptake of nitrogen.
  • Too High: Excessive sulfur levels can acidify (reduce) the soil pH and cause nutrient imbalances. But sulfur toxicity is rare unless you apply an excessive amount of sulfate fertilizer or your soil is especially acidic.
  • Ideal: The optimal range is 29-36 ppm, but many organic-matter-rich soils can be much higher without causing problems. Do not be alarmed if your soil test shows sulfur levels from 50-100 ppm.
  • Too Low: Sulfur deficiency mostly appears as yellowing new leaves due to a lack of photosynthesis and nitrogen metabolism.
  • Recommended Amendments: Compost, animal manure, straw, mulch, gypsum, and langbeinite can add sulfur to the soil.

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)

Close-up of a cow manure on green grass in a sunny garden.
Ensure zinc adequacy with organic matter in soil enrichment.

  • What is It? This mineral naturally comes from rocks and is an essential micronutrient for plants.
  • Importance: Plants need zinc to form chlorophyll, form plant hormones (auxins), and withstand cold temperatures.
  • Too High: Zinc toxicity is rare and mostly occurs in cereal crops like wheat or barley.
  • Ideal: The recommended range for zinc is 3.5-8.1 ppm, but many soils have 10-150 ppm without issues.
  • Too Low: Soils with low organic matter generally lack zinc, but zinc deficiency is fairly rare. Acidic and sandy soils are most prone to zinc deficiency, which causes stunted plants with pale green foliage or yellowing spots between the leaf veins.
  • Recommended Amendments: Manure, compost, and micronutrient blends like langbeinite and liquid humate can boost zinc availability. 

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)

Top view of a carrot with orange oblong root and green lacy leaves on loose soil in the garden.
Boost plant health with manganese for optimal growth and functioning.

  • What is It? Manganese is a plant micronutrient needed in very small quantities. This mineral comes from ancient sedimentary rocks.
  • Importance: Plants need manganese for growth, enzyme activation, and metabolism.
  • Too High: Manganese toxicity causes brown spots on older leaves and yellowing on younger leaves. It mostly occurs in acidic, poorly drained soil.
  • Ideal: The optimal range is 21-51 ppm, but a bit higher is no problem.
  • Too Low: Deficient plants may have contorted, stunted growth and interveinal chlorosis. Sandy tropical soils have the most problems with manganese deficiency because the nutrient leaches out with rain or irrigation.
  • Recommended Amendments: Add more carrot tops to your compost pile or mix into the soil.

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)

Close-up of a woman's hand applying white granular fertilizer into black, loose soil in a sunny garden.
Revitalize plants with iron for vibrant, healthy foliage.

  • What is It? Iron is a plant micronutrient that comes from rock minerals and is required to synthesize chlorophyll.
  • Importance: Plants need iron to form chlorophyll, structure chloroplasts, and perform photosynthesis.
  • Too High: Excessive iron (over 500 ppm) can damage cell membranes and stunt or kill plants. Symptoms are bronzing leaves and stunted roots.
  • Ideal: The optimal iron range is 11-51 ppm, but garden soils can reach up to 300 ppm without issue.
  • Too Low: Iron deficiencies usually manifest as chlorotic (yellow) young leaves and slow growth.
  • Recommended Amendments: Blood meal, chelated iron or iron sulfate fertilizers are often used for deficiencies, but adding manure and compost can also boost plant-available iron in the soil.

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)

Close-up of chicken paws walking on loose wet soil.
Maintain soil health with balanced micronutrients and compost enrichment.

  • What is It? Copper is a plant micronutrient and trace metal element that naturally occurs deep in the Earth.
  • Importance: Plants need copper in very small quantities to form enzymes that create chlorophyll.
  • Too High: Copper toxicity can occur when copper fungicides, pesticides, sewage sludge, or manure are overused.
  • Ideal: The recommended range is 1.6 to 3.1 ppm.
  • Too Low: Copper deficiency results in purple or blue, darkened leaves with pale tips and edges.
  • Recommended Amendments: The best way to fix copper deficiency is to apply poultry manure or amino-copper chelate.

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)

Close-up of a woman's hands holding loose, fresh black soil near a bed of growing strawberry plants.
Ensure robust plant growth with adequate boron supplementation.

  • What is It? Boron is a trace mineral that comes from decomposing soil organic matter.
  • Importance: Plants need boron in very small amounts to form cell walls and aid in other growth factors. Plants cannot properly flower and fruit without boron.
  • Too High: High boron levels (above 5.0 ppm) can inhibit root growth and cause leaves to cup downward or drop.
  • Ideal: The optimal boron range is 1.3 to 2.6 ppm, but levels up to 4.0 are not typically problematic.
  • Too Low: Boron deficiency can cause flowers and fruit to “abort” or fall off the plant. The leaves may appear brittle and distorted. Deficiency is most common in soils with low organic matter.
  • Recommended Amendments: Boric acid (borax) is a home remedy for boron issues in the garden, but it should only be applied in very small amounts. Trace minerals like azomite and langbeinite are another common solution for this micronutrient deficiency. Regular applications of microbially-rich compost ensure proper availability. 

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?

Close-up of a farmer's hand checking the quality of the soil in a bed with various young seedlings growing.
Nitrogen’s mobility defies soil tests.

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.

Final Thoughts

Soil tests may seem complicated, but you don’t need to know everything about plant nutrition to put your results to use. Instead, just focus on anything that shows up as deficient, and amend with the recommended fertilizers. On the flip side, know when to dilute with native dirt or a non-soil material.

Match any deficient results with plant growth symptoms you notice in the garden. Regular applications of quality compost help ensure a balance of minerals and micronutrients to keep your plants healthy and happy.

Close-up of a gardener's hand in a blue glove pouring synthetic fertilizers onto a plant with large succulent green leaves in the garden. The plant forms a rosette of large, strong, vertical, succulent green leaves with reddish and pointed tips. Fertilizers are granular and white.

Soil Improvement

Do Synthetic Fertilizers Harm the Soil?

Healthy soil is a gardener’s most valuable resource, but certain products can disrupt the natural belowground ecology. If you are concerned about synthetic fertilizers harming your soil, here is what to look out for, explained by a soil expert and former farmer.

NPK fertilizer. Close-up of a garden trowel filled with NPK fertilizer next to a watermelon plant. Fertilizers are granular and have blue ball-shaped granules.


What Is NPK? Understanding Garden Fertilizers

All plants require nutrients to grow, but it can be difficult to understand how to apply fertilizers and the necessary nutrients. Learning about the NPK ratio is a great place to start your journey into the fertilizer world. In this article, vegetable farmer Briana Yablonski will explain what NPK means and how you can use it to select the best fertilizer for your garden.

Spring fertilizing. Close-up of a gardener's hand in a black glove applying fertilizer to young lettuce in the spring garden. He applies fertilizer with a blue garden trowel. The salad has a rosette of oval, oblong, wide green leaves.


11 Tips for Fertilizing Your Garden this Spring

As your garden awakens from a cold, dormant winter, now is the time to nourish your plants for a flourishing season ahead. Former organic farmer and garden expert Logan Hailey explains 11 essential tips for optimizing spring fertilization.

The striking blooms of crimson clover grow as a fall cover crop.

Soil Improvement

9 Fall Cover Crops for Fertile Spring Soil

Nourish your soil all winter with fall-seeded cover crops that protect from erosion, improve fertility, and break up soil compaction. Former organic farmer Logan Hailey shares the top 9 science-backed cover crop species, plus the best ways to terminate them in the spring.