How to Read a Soil Test Jacksonville

You've sent off your soil sample and the results just came back. Now you're staring at a report full of numbers, abbreviations, and recommendations that might as well be written in another language. I see this confusion all the time with Jacksonville homeowners who know soil testing is important but have no idea what to do with the results.

A soil test is the single most useful tool for understanding what's happening underground in your yard. It tells you exactly what your soil has, what it's missing, and what adjustments you need to make before you waste money on fertilizers or amendments you don't need.

But only if you can actually read the report.

Jacksonville soils present unique challenges. We've got everything from pure sand near the beaches to heavy clay inland, and most areas fall somewhere in between. Understanding your specific soil chemistry determines whether your lawn, garden, or landscape thrives or just survives.

Here's how to make sense of that soil test report.

Understanding the Basic Numbers

Most soil test reports from the UF/IFAS Extension lab or private testing companies follow a similar format. You'll see several sections covering pH, major nutrients, minor nutrients, and sometimes organic matter content.

pH: The Foundation of Everything

This is the first number you should look at, and it's the most important for Jacksonville soils.

pH measures soil acidity or alkalinity on a scale from 0 to 14. Seven is neutral. Below 7 is acidic, above 7 is alkaline.

For Jacksonville lawns: Most warm-season grasses (St. Augustine, Bahia, Zoysia, Bermuda) prefer a pH between 6.0 and 7.0. This is the sweet spot where nutrients are most available to plants.

For vegetable gardens: Most vegetables want pH between 6.0 and 6.8.

For azaleas and acid-loving plants: Target 5.0 to 6.0.

Here's why this matters: even if your soil has adequate nutrients, plants can't access them if pH is too far out of range. Iron becomes unavailable in alkaline soils, which is why you see so many Jacksonville lawns with yellowing St. Augustine even after fertilization.

Sandy soils in Jacksonville tend to be slightly acidic (5.5-6.5), while clay soils can be more neutral to slightly alkaline. Coastal areas sometimes see higher pH due to shell fragments and salt influence.

If your pH is too low (too acidic): Add lime. Your report should recommend pounds per 1,000 square feet. Dolomitic lime is common because it provides both calcium and magnesium. Apply in fall or early spring and water it in. It takes several months to change soil pH, so don't expect instant results.

If your pH is too high (too alkaline): Add sulfur or an acidifying fertilizer. This is less common in Jacksonville than low pH, but it happens, especially in areas with construction debris or where builders have mixed in concrete waste. Elemental sulfur works slowly. Aluminum sulfate works faster but can damage plants if overused.

Primary Macronutrients: NPK

You'll see three numbers prominently displayed on any fertilizer bag: nitrogen (N), phosphorus (P), and potassium (K). Your soil test breaks down what you already have.

Nitrogen (N)

This is the nutrient plants use most. It drives green growth and leaf development.

Here's the thing about nitrogen: it moves through soil quickly, especially in Jacksonville's sandy soils. Rain and irrigation leach it into groundwater. That's why soil tests often show low nitrogen levels even if you fertilized recently.

Most soil test reports don't give detailed nitrogen recommendations for this reason. They assume you'll need to add it regularly. For Jacksonville lawns, that typically means 2-4 pounds of nitrogen per 1,000 square feet per year, split into multiple applications.

Phosphorus (P)

Phosphorus supports root development, flowering, and fruiting. It doesn't move through soil like nitrogen—it stays put.

Many Jacksonville soils test adequate or even high in phosphorus, especially if they've been fertilized regularly in the past. Over-application leads to phosphorus runoff into waterways, contributing to algae blooms and water quality problems.

Reading phosphorus levels:

• Low: Below 30 ppm (parts per million)
• Medium: 30-60 ppm
• High: Above 60 ppm

If your test shows medium to high phosphorus, you don't need to add more. Look for fertilizers with little or no phosphorus (the middle number in the NPK ratio). A fertilizer labeled 15-0-15 has no phosphorus.

The St. Johns River Water Management District and local ordinances restrict phosphorus in fertilizers for established lawns. Your soil test results can justify phosphorus application if you truly need it.

Potassium (K)

Potassium strengthens cell walls, improves drought tolerance, and helps plants resist disease. Jacksonville's sandy soils often test low in potassium because it leaches out, though not as quickly as nitrogen.

Reading potassium levels:

• Low: Below 40 ppm
• Medium: 40-125 ppm
• High: Above 125 ppm

If your test shows low potassium, your fertilizer should include it (the third number in the NPK ratio). Potassium sulfate and potassium chloride are common sources.

For established lawns, 1-2 pounds of potassium per 1,000 square feet per year typically maintains adequate levels. Sandy soils need more frequent applications.

Secondary Nutrients

These are called "secondary" but they're not optional. Plants need them, just in smaller quantities than NPK.

Calcium (Ca)

Calcium is essential for cell wall structure. Most Jacksonville soils have adequate calcium, especially if you've applied lime in the past.

Reading calcium levels:

• Low: Below 400 ppm
• Medium: 400-800 ppm
• High: Above 800 ppm

Dolomitic lime provides calcium. Gypsum (calcium sulfate) adds calcium without changing pH, which is useful if you need calcium but your pH is already in the right range.

Magnesium (Mg)

Magnesium is the central atom in chlorophyll, so without it, plants can't photosynthesize effectively. Deficiency symptoms look like yellowing between leaf veins.

Reading magnesium levels:

• Low: Below 40 ppm
• Medium: 40-120 ppm
• High: Above 120 ppm

Sandy soils often test low in magnesium. Dolomitic lime provides both calcium and magnesium. Epsom salt (magnesium sulfate) is a quick fix for deficiencies but doesn't provide long-term availability.

Sulfur (S)

Sulfur is necessary for protein synthesis and enzyme function. Jacksonville soils sometimes test low, especially sandy soils that have been heavily leached.

If sulfur is low, amendments like potassium sulfate, ammonium sulfate, or elemental sulfur provide it. Many granular fertilizers include sulfur.

Micronutrients: Small but Critical

Plants need micronutrients in tiny amounts, but deficiencies create visible problems.

Iron (Fe)

Iron deficiency is extremely common in Jacksonville, especially in alkaline soils or soils with high pH. You'll see it as yellowing leaves with green veins, typically on new growth first.

The irony: soil tests often show adequate iron, but it's chemically unavailable to plants at higher pH levels. This is why adjusting pH matters more than just adding iron.

For quick fixes, chelated iron provides temporary relief. Long-term solutions require lowering pH to make existing iron available.

Manganese (Mn)

Manganese deficiency shows up similarly to iron deficiency. It's less common in Jacksonville but does occur in alkaline or poorly drained soils.

Other Micronutrients

Your report may include copper (Cu), zinc (Zn), and boron (B). Deficiencies are rare in home lawns but can occur in vegetable gardens or areas with heavily leached sandy soil.

Most complete fertilizers include micronutrients. If your test shows specific deficiencies, targeted amendments are more effective than guessing.

Organic Matter and CEC

Some soil test reports include organic matter content and cation exchange capacity (CEC).

Organic Matter

This measures the percentage of decomposed plant and animal material in your soil. Jacksonville's sandy soils typically test very low—often 1-2% or less.

Organic matter improves water retention, provides slow-release nutrients, and supports beneficial soil organisms. Adding compost, aged manure, or other organic materials improves soil quality over time.

For lawns, leaving grass clippings adds organic matter. For gardens, working in compost before planting makes a noticeable difference.

Cation Exchange Capacity (CEC)

CEC measures your soil's ability to hold and release nutrients. It's expressed in milliequivalents per 100 grams (meq/100g).

Reading CEC values:

• Low (sandy soil): Below 10
• Medium (loamy soil): 10-20
• High (clay soil): Above 20

Sandy Jacksonville soils typically have low CEC, meaning they don't hold nutrients well. Clay soils have higher CEC. You can't change CEC quickly, but adding organic matter gradually improves it.

Low CEC soils need more frequent, smaller fertilizer applications because they can't hold nutrients for extended periods.

Making Sense of Recommendations

Most soil test reports include amendment recommendations. They'll say something like "Apply 50 pounds of dolomitic lime per 1,000 square feet" or "Use 1 pound of nitrogen per 1,000 square feet per growing season."

Here's how to use those numbers:

Calculate your area: Measure your lawn or garden bed in square feet. For rectangular areas, multiply length by width. For irregular shapes, break them into sections and add them up.

Convert recommendations: If the report recommends 50 pounds per 1,000 square feet and you have 3,000 square feet, you need 150 pounds total.

Choose products: Read fertilizer and amendment labels carefully. A 50-pound bag of lime covers a specific area based on application rate. Do the math to determine how many bags you need.

Timing matters: Lime works slowly. Apply it in fall or early spring. Sulfur also takes time. Fertilizers work faster but should be applied according to local ordinances (in Jacksonville, no fertilizer during the summer rainy season blackout period).

Jacksonville-Specific Considerations

Sandy Soils

If your soil test came back with low CEC, low organic matter, and deficiencies in multiple nutrients, you've got typical Jacksonville sandy soil.

Amendments leach through sand quickly. You need:

• More frequent fertilizer applications in smaller amounts
• Slow-release fertilizers that provide nutrients over time
• Regular additions of organic matter
• Consistent irrigation to move nutrients into the root zone

Clay Soils

Clay holds nutrients better but drains poorly. If your soil test shows high CEC and adequate nutrients but your plants still struggle, drainage is likely the issue.

Consider:

• Raised beds for gardens
• Amending with compost to improve structure
• Avoiding overwatering, which clay doesn't tolerate

Coastal Areas

Salt accumulation affects nutrient availability. If you're near the beach and seeing poor plant performance despite decent soil test numbers, salt may be the hidden problem.

Gypsum helps leach salts from the root zone. Regular irrigation (when appropriate) pushes salts deeper.

What to Do with Your Results

Now that you understand the numbers, take action:

1. Adjust pH first. This makes everything else more effective.

2. Address major deficiencies. If phosphorus or potassium is low, correct it before regular fertilization.

3. Develop a fertilization plan. Use the soil test to choose fertilizers with the right NPK ratio for your needs.

4. Add organic matter. Almost every Jacksonville soil benefits from this.

5. Retest in 2-3 years. Soil chemistry changes. Regular testing keeps you on track.

The Bottom Line

A soil test is only useful if you understand what it's telling you. Jacksonville's diverse soils mean no one-size-fits-all approach works. What your neighbor needs might be completely different from what your yard needs.

Take the time to read your report carefully. Focus on pH first, then macronutrients, then everything else. Use the recommendations to make informed decisions about amendments and fertilizers.

You'll save money by not applying products you don't need, and you'll get better results because you're addressing actual deficiencies rather than guessing. That's the whole point of soil testing.