Know your soil before you plant in it
Texture, organic matter and pH; how to take a soil sample and read the lab report; and what lead screening levels mean for where you grow food.
Start here Essentials
This module asks you to learn what is in the ground before you plant: send one sample, ask about lead where it applies, and act on the report. Everything marked Go deeper is optional on a first pass.
- Decide whether you need a sample. In-ground beds and plots do. Containers of bagged mix do not; go on to Module 4. Taking a sample.
- Send one composite sample. Call 811 before you dig. Take your lab's number of scoops from one area, at its depth, and air-dry them without heat. Not within 6 to 8 weeks of lime or fertilizer.
- Ask for lead if a building nearby dates from before 1978, the garden is near a busy road, the fill or history is unknown, or purchased topsoil comes with no test results. Lead.
- Read the report in order, copy its values and recommendations as printed, and add lime or sulfur only if the report recommends it. Reading the lab report.
- If lead was tested, find your row in the tier table and follow EPA's column. Ask your health department or a physician what the result means for anyone's health.
Minimum time: about 30 minutes to sample and pack, plus the lab's turnaround. Done when: a sample is sent or results are in hand, or you have chosen bagged mix in containers.
1. Texture: what the soil is made of Understand
Soil is mineral particles, organic matter, water and air. Oregon State University Extension's Improving garden soils with organic matter (EC 1561) says that in a productive soil, 40 to 60 percent of the volume is pore space, filled with water or air. Roots and soil organisms need both. Everything in this module comes back to that: how much space there is between particles, how big the spaces are, and whether they stay open.
The mineral particles come in three size classes. Sand is the largest, silt is in the middle, and clay is the smallest. EC 1561 gives a scale for the difference: if a sand grain were a basketball, a silt particle would be about a marble and a clay particle about the dot a sharp pencil makes. The proportion of the three in a soil is its soil texture.
Physical principle Texture decides how water moves. EC 1561 explains that sandy soils drain fast and need frequent watering, while clay soils hold a lot of water but give up only part of it to roots, and let air and water through slowly. The reason is pore size. Large particles leave large pores that drain; tiny, flat clay particles pack tightly and leave pores so small that water clings in them. A loam, which has a balance of the three, sits between the extremes.
You cannot change texture by adding sand
Gardeners with heavy clay often think of mixing in sand. Physical principle EC 1561 says not to. Clay particles coat the sand grains and the mix can set like concrete, harder to manage than the clay was. It states the point bluntly: "Like diamonds, clay soils are forever" (Oregon State University Extension, EC 1561). Texture is a fixed property of a site at garden scale. What you can change is structure and organic matter, which the next section covers. If the texture is a real obstacle, the answer is usually a raised bed with imported fill, which Module 4 compares with the other options.
The jar test: an estimate you can make at home
The jar test separates a soil sample into its three particle sizes by letting them settle out of water. Large particles fall first and fine ones last, so the layers stack in order. Clemson Cooperative Extension's Home and Garden Information Center fact sheet Soil Texture Analysis: The Jar Test (HGIC 1656) gives the method:
- Sift the soil through a mesh sieve or colander to remove rocks, roots and large debris.
- Fill a straight-sided clear jar about one third full with the sifted soil, then fill most of the rest with clean water, leaving space at the top.
- Cap and shake until the soil is a uniform slurry, then set the jar on a level surface where it will not be moved.
- At 1 minute, mark the top of the sand layer. Sand settles almost at once.
- At 2 hours, mark the top of the silt layer.
- At 48 hours, mark the top of the clay layer. Measure each layer and the total height with a ruler.
- Compute each percentage as the layer's height divided by the total height, times 100, and find the texture class where the three percentages meet on a texture triangle (the standard chart that names a soil, such as "clay loam," from its sand, silt and clay percentages).
Clemson's printable worksheet labels the clay line as silt. Use the method, not the worksheet; the texture sheet in the soil record has fields for the three heights and percentages.
| Texture leaning toward | Water | Air | What it means for the gardener |
|---|---|---|---|
| Sand | Drains fast; holds little | Plenty | Water more often; organic matter raises water storage |
| Silt | Between sand and clay | Between sand and clay | Fine particles; like any soil, protect its structure by staying off it when wet |
| Clay | Holds a lot; much of it unavailable to roots | Little; slow to drain | Work it only when it is not wet; add organic matter, never sand |
A jar test estimates texture. It is not a lab analysis. Organic matter floats or stays suspended, the water may still be cloudy at the last reading, and a layer boundary is a judgment call by eye. Use the result to describe the soil in words ("mostly clay," "sandy loam") and to explain what you see when you water. If a decision depends on exact percentages, a soil lab can run a particle-size analysis; UMass Amherst's soil lab, for example, lists one among its services.
2. Organic matter and structure
Organic matter is the part of the soil that comes from living things: roots, leaves, compost, manure, and the bodies and byproducts of soil organisms, in every stage of decay. It is a small share of most soils by weight, but it does more than its share of the work.
EC 1561 lists what organic matter changes. It lets the soil take in and store more water, so a well-amended garden can need less watering, especially under mulch. It feeds soil organisms, which cycle nutrients, so over time an amended soil supplies more of what plants need and less fertilizer is required. And because more water soaks in and less runs off, fertilizer and pesticide stay in the soil instead of washing into waterways.
Structure: how particles clump
Soil structure is the way particles bind into larger crumbs and clods, and the pore spaces between them. EC 1561 describes the ideal topsoil as granular, made of small crumbs, which digs easily, takes in water and makes a good seedbed. The crumbs form when bacteria feeding on organic matter release sticky substances that glue particles together. So organic matter changes structure, while texture stays put. Physical principle A clay soil stays a clay soil, but a clay soil with good structure has stable crumbs with larger pores between them, and drains and breathes far better than the same clay compacted.
Compaction is the crushing of those pores, by feet, machines or working the soil when it is wet. EC 1561 compares good structure to a sponge and poor structure to a bowl of popcorn: one keeps its pores under pressure and one does not. It also warns that tilling, especially wet soil, damages structure and speeds the loss of organic matter. This is why the beds in Module 4 are sized so you do not need to step in them.
Fresh material and compost behave differently Go deeper
EC 1561 reports that about half of fresh organic matter (green leaves, fresh plant waste) is lost as carbon dioxide in the first 60 days after it goes into the soil, while about half of composted organic matter is lost over one to two years. Fresh material feeds organisms hard and briefly, and produces more of the glue that builds crumbs. Compost lasts longer, carries fewer weed seeds and disease organisms, and is the usual choice for vegetable beds. EC 1561 prefers composted manure over fresh manure to avoid contaminating food crops with pathogens such as E. coli; Module 11 covers manure timing before harvest.
Checking organic matter without a lab
EC 1561 gives four quick checks. Each is Test it evidence, not a measurement:
- Look. Soils with enough organic matter are darker.
- Watch after rain. Puddles that sit for a long time suggest unstable pores.
- Rub a pinch. Crumbs that hold together are aggregation at work.
- Smell. A rich earthy smell is a good sign; a foul smell suggests poor air movement.
A lab can measure organic matter as a percentage, usually as an optional add-on to the routine test (both Penn State's and UMass Amherst's labs list it that way). University of Maryland Extension's Soil to Fill Raised Beds gives a target for raised beds containing garden soil: 25 to 50 percent organic matter by volume, which a lab reports as 5 to 15 percent by weight. Convention The two numbers describe the same soil; a lab weighs, and compost is light, so the weight figure is much smaller than the volume figure.
How much compost to add, and when, is a Module 4 and Module 9 question. For scale, EC 1561 works out that a 1-inch layer over 100 square feet is about 8 cubic feet, or about 12 five-gallon buckets, and that a 1-inch layer over 200 square feet is 0.6 cubic yards. The amendments sheet is where you record what you add.
3. Taking a sample and choosing a lab
A soil test is only as good as the sample. UMass Amherst's lab says it directly in its sampling instructions: a poor sample can produce wrong recommendations. A garden can vary from one end to the other, so a lab asks for many small scoops mixed together rather than one spadeful.
Each scoop is a subsample. Mixed together, they make a composite sample, which stands for the average of the area you scooped. The lab tests about a cup of that mixture.
Define the area first
UMass asks you to sample one area at a time, where the soil looks similar and has had similar care: the same color, texture, slope, drainage and history. A vegetable bed by the house foundation and a bed at the back of the yard are two areas. So are a spot where a shed once stood and the open lawn beside it. Draw a rough map before you dig and give each area a name; that name becomes the sample ID on the lab form.
Three labs, three sets of instructions
Extension labs agree on the shape of the method and differ on the numbers. Convention Follow the instructions of the lab you send to, because its recommendations are calibrated to its own method.
| Source | Subsamples | Depth | Handling | Timing notes |
|---|---|---|---|---|
| UMass Amherst Soil and Plant Nutrient Testing Laboratory | 12 or more, random spots, not the edges | 6 to 8 in | Mix, remove stones and roots, air-dry about 1 cup on paper; a fan on low is fine, no heat | Not when very wet, and not within 6 to 8 weeks after lime or fertilizer |
| Penn State Agricultural Analytical Services Lab | At least 13 places | 6 in (or plow depth) | Mix into one composite, air-dry overnight in a warm room, no heat; send 1 cup | Sample areas with different lime or fertilizer history separately |
| University of Nebraska-Lincoln Extension, G945 | 10 to 15 cores, random | 8 in | One bulk sample per garden unless soils differ | A test every fifth year is enough unless a major amendment went on since |
The labs give the timing rule without spelling out the reason. The plain one is that fresh lime or fertilizer has not yet reacted or spread through the soil, so a scoop can catch a concentrated spot and misreport the bed. Both labs also specify air-drying without heat; follow that exactly rather than speeding it up in an oven.
Choosing a lab and the tests to ask for
Most states have a university soil lab tied to the extension service; the Extension Foundation's directory, Find Extension in Your State, links to each one. Your county extension office can tell you which lab serves you, what it costs and how to send the sample. Fees vary by lab; check the current price on the lab's own page.
Before you mail anything, read what the lab's routine test includes. They differ:
- Penn State's standard test reports pH, a lime requirement, and phosphorus, potassium, magnesium and calcium, with lime and fertilizer recommendations for the crop you name. Organic matter is an extra.
- UMass Amherst's routine test reports pH, acidity, a set of nutrients (phosphorus, potassium, calcium, magnesium and several micronutrients), lead, aluminum, cation exchange capacity and base saturation, with recommendations. Organic matter, soluble salts and nitrate are extras.
So lead is part of the routine test at one lab and not mentioned at the other. If anything in the lead section applies to your site, ask the lab directly whether lead is included or must be added. UMass also notes that without a crop code on the form, it cannot give lime and nutrient recommendations; write "vegetable garden" or the code the form lists.
Home test kits exist for pH and nutrients, and for lead. The New York Soil Health fact sheet on lead (Cornell) classes home lead kits and portable X-ray fluorescence readings as screening tools and certified or university labs as the most accurate. Convention Treat a kit result as a reason to send a lab sample, not as the answer.
4. Reading the lab report
A report has three kinds of content: measured values, a rating of each value (often low, optimum, high), and recommendations. Copy all three into the soil record exactly as printed, with units. Recommendations are the part you act on; the measured values are what you compare next time.
pH Go deeper
pH is a measure of how acidic or alkaline the soil is. University of Nebraska-Lincoln Extension's Fertilizers for Vegetables in Home Gardens (G945) explains that soil reports usually fall between 4.5 and 8.5; 7.0 is neutral, below 7.0 is acidic and above is alkaline. Physical principle pH matters because it controls how available many nutrients are to roots. A soil can contain plenty of a nutrient that the plant cannot take up at the wrong pH.
Sources give slightly different target ranges, and each is a convention tied to its purpose:
| Source | Target | Context |
|---|---|---|
| University of Nebraska-Lincoln, G945 | 6.5 ideal for most vegetables; change often needed below 5.5 or above 7.5 | Nutrient availability |
| University of Maryland, Soil to Fill Raised Beds | 6.2 to 6.8 | Most annuals, perennials and vegetables |
| U.S. EPA, healthy gardening practices | Near neutral, 6.5 to 7.5 | Reducing lead uptake by plants |
| New York Soil Health (Cornell), lead fact sheet | Near neutral, 6.5 to 7 | Gardening where lead is present |
We do not average these. Read the target the lab printed for your crop; if lead is part of your picture, note that EPA and Cornell both favor the near-neutral end.
Lime requirement and buffer pH
Soil pH tells you where the soil is. It does not tell you how hard the soil will resist being moved, and soils differ: G945's table for lowering pH, for example, gives different amounts of sulfur for different textures. Labs measure that resistance with a second reading, the buffer pH, and use it to compute the lime requirement: the amount of lime needed to bring the soil to the target pH. G945 explains that its rate depends on the buffer pH and on the lime material's neutralizing value, which is printed on the lime bag, and that rates are given per 1,000 square feet. Penn State's report calls the same idea the Mehlich buffer lime requirement.
To use a per-1,000-square-foot rate on a smaller garden, scale by area: your area divided by 1,000, times the rate. The fertilizer calculator does this conversion for any recommendation you already hold. It does not create a recommendation.
Why lime and sulfur follow a test, not a guess
G945 gives three reasons, each of which has caught gardeners out:
- They are slow. Lime can take one to three years for the pH to peak. Elemental sulfur, which lowers pH, may take a year or more, and G945 says to retest one to two years after applying it. A mistake made by eye lasts for seasons.
- Too much does harm. G945 warns against over-liming: excess lime is likely to cause iron chlorosis, a yellowing between the leaf veins.
- Lowering pH is hard. G945 notes that lowering a high pH is generally not practical over large areas, and that irrigation water high in calcium carbonate can undo sulfur over time. It may be feasible in a small plot.
The same logic applies to the kitchen-scrap remedies gardeners trade, such as coffee grounds, eggshells or Epsom salts. Convention Only a soil test tells you what your soil lacks, so we do not repeat amendment folklore here.
Phosphorus, potassium and the rest
Phosphorus and potassium are reported as a measured amount and a rating. The number depends on the chemical extraction the lab uses: Penn State uses Mehlich 3, UMass uses Modified Morgan, and G945 names the Bray and Olsen tests used in Nebraska. Convention Read your lab's rating and recommendation rather than comparing your raw number with a chart from another lab or another method. For the same reason, stay with one lab from year to year if you want the numbers to compare.
Nitrogen is often missing from a routine report. UMass offers a nitrate test as an extra but says the result changes too quickly in its climate to base recommendations on. Most labs instead print a nitrogen recommendation by crop. Module 9 turns a recommendation into an amount of a product you can buy.
What a soil test cannot tell you
UMass lists what a fertility test does not identify: problems from drainage, insects, plant diseases, weeds, winter injury or misused pesticides. If plants struggle on a soil with a good report, the cause is elsewhere; Module 10 covers diagnosis.
Reading order for a new report. Sample ID and date (is it the right bed?). pH and the target. The lime or sulfur recommendation and its unit. Phosphorus and potassium ratings. Organic matter, if tested. Lead or other metals, if tested, with units (ppm or mg/kg). Then the written recommendations, copied word for word.
5. Lead and other contaminants
Lead occurs naturally in soil at low levels. Human activity has added much more in some places. Cornell's Healthy Soils, Healthy Communities project lists where higher levels tend to be found: near older painted structures, busy roads, old orchard land, factories and other industry, and treated lumber. The New York Soil Health fact sheet names leaded gasoline and lead paint as the historic sources. That is why the age of nearby buildings matters: this course's safety notes treat a house built before 1978 as a reason to test.
Physical principle You cannot see lead in soil. Cornell's project notes that plants can grow well in soil high in lead, so a healthy-looking garden says nothing either way. Only a test answers the question. Cornell also notes that signs of past burning or chemical spills, such as stains or odors, point to other contaminants; describe them to the lab or the health department when you ask about testing.
How lead reaches people from a garden
EPA's Healthy Gardening Practices to Reduce Exposure to Lead-Contaminated Soil lists four routes: eating produce that absorbed lead from soil, eating produce with contaminated soil still on it, tracking soil indoors on shoes, clothes and tools, and swallowing or breathing soil dust while working. Most of the practices tied to lead tiers address the last three. That is why mulch, clean fill, washing, peeling and leaving shoes at the door appear in every tier.
Cornell Cooperative Extension NYC's Healthy Soils, Healthy Communities research is the kind of work behind this guidance. From 2008 to 2011 it sampled more than 80 New York City community gardens, collecting over 900 soil samples, and paired nearly 200 vegetable samples with soil samples to compare crop types.
Units and screening levels
Lead results come in parts per million (ppm) or milligrams per kilogram (mg/kg). They are the same number: 100 ppm is 100 mg/kg. A screening level is a concentration that agencies use to decide when a site needs a closer look or a change in use. It is a decision line, not a statement that soil just below it is harmless or that soil just above it will harm someone.
Two kinds of number appear in lead guidance, and they answer different questions. A cleanup screening level tells an agency when a contaminated site needs investigation. A gardening tier tells a gardener where to grow which crops. The gardening table below uses only gardening tiers. Convention
The cleanup number has changed twice recently. In January 2024, EPA issued updated soil lead guidance for Superfund (CERCLA) sites and RCRA corrective action facilities that lowered the residential screening level from 400 ppm to 200 ppm, with 100 ppm where there were additional lead sources. The New York Soil Health fact sheet, dated November 2024, reports that guidance. On October 16, 2025, EPA issued a directive that supersedes the January 2024 guidance for those same cleanup programs. It keeps a regional screening level of 200 ppm for residential soil and sets a removal management level of 600 ppm. The October 2025 directive does not mention a 100 ppm level, and it does not address gardening. EPA's gardening page, as we read it on 2026-10-10, still organizes its advice around 200 and 400 ppm. The Cornell sheet's tiers are its own gardening guidance and are labelled with their November 2024 date.
EPA and Cornell tiers side by side
EPA and New York Soil Health (Cornell) both tie gardening actions to soil lead levels. Cornell's tiers are stricter and start lower. Convention These are published guidance, not regulation, and we show both rather than blending them.
| Soil lead (ppm) | EPA, Healthy Gardening Practices | New York Soil Health (Cornell), November 2024 |
|---|---|---|
| Under 63 | "Approaching 200 ppm: Exercise Caution" (no lower bound given). Wash hands, produce and clothes; wear gloves; limit gardening while pregnant or nursing. Root and shallow-rooted crops in existing soil; deep-rooted crops in raised beds. | Typical background. No added precautions and no crop restrictions. Cornell defines "clean soil" as under 63 ppm. |
| 63 to 99 | Above background. More amendments and barriers; consider not growing root crops. | |
| 100 to 199 | Suggests contamination. Raised beds with clean soil; consider not growing leafy greens or root crops, and favor fruiting crops. | |
| 200 to 399 | "200 to 400 ppm: Modifications to Existing Soil Needed." Raised beds of clean soil and organic matter; cover bare soil; peel root vegetables; root and shallow-rooted crops in raised beds; deep-rooted crops not recommended even in raised beds, except in containers. | Grow only in raised beds with clean soil; keep all other soil covered. (The sheet also notes that this range is at or above EPA's 200 ppm cleanup screening level.) |
| 400 and over | "Over 400 ppm: Do Not Use Existing Soil." Shallow-rooted crops only in raised beds with at least 16 in of clean soil over garden fabric, or in containers; root and deep-rooted crops only in containers; cover or dampen bare soil; add clean soil and organic matter each year. | 400 to 1,200: EPA's "soil lead hazard" level for bare soil where children play. Raised beds with clean soil only; keep other soil covered; removal and replacement may be needed. Some states set lower thresholds. |
Read the table by row, then by column. At 140 ppm, for example, EPA's page puts you in its caution tier and Cornell's sheet asks for raised beds of clean soil. Where the two differ, the stricter one is the more cautious choice, and the choice is yours to make with the people named in the boundary below.
Some practices apply at every level. EPA's page lists: wash hands, toys, tools and clothes after gardening; wear gloves; keep children and pets out of the garden while lead levels are unknown; take shoes off at the door; mulch to keep soil off crops; build raised beds on a visible barrier such as garden fabric; locate gardens away from old painted buildings and heavy traffic; discard the outer leaves of leafy vegetables, wash produce, and peel root crops. The Cornell sheet adds stones or wood chips on paths and advises against treated or painted wood, railroad ties and telephone poles as bed material (Module 4 compares that advice with Oregon State's lumber study).
This section explains what EPA's and Cornell's published tiers say about where to grow food, and it stops there. Whether a lead result is a health concern for your household, and especially for children or anyone pregnant, is a question for your local health department or a physician. The Cornell sheet suggests considering blood lead testing for children; that decision belongs in a conversation with a pediatrician. We do not interpret a result for a person, and a garden-tier match is not a health clearance.
When to test for lead
Ask the lab for a lead test along with the routine test if any of these apply: the house or a nearby building was built before 1978; the garden is near a busy road; the site has unknown fill or a history you do not know; or you plan to buy topsoil and the supplier has no test results. EPA lists three places to get a test: some local health departments, university and extension labs, and soilSHOP screening events. Sample each area separately, because the Cornell sheet notes that lead can vary across a site or even within a small area. The drip line of an old painted house and the far corner of the lot can differ widely.
If you will grow only in containers of bagged mix, the yard's lead result does not change what is in the pots. It still matters for children playing in bare soil nearby and for soil tracked indoors.
6. See it See it
Both examples below use the course's fictional cases. The test results are invented for teaching; they are not data for any real place.
The Okafor garden: a 1952 house and a lead result. Ada and Chidi Okafor have two children, 6 and 9, and a back lawn they want to turn into two 4 x 8 ft vegetable beds. The house was built in 1952, so before they bought any lumber they sent a composite yard sample to their state university lab with the lead test added. The result: 140 ppm lead.
They read the tier table by row. EPA's page puts 140 ppm in its "approaching 200" caution tier, which would allow root crops in the existing soil. The Cornell sheet puts 140 ppm in its 100 to 199 tier: raised beds with clean soil, favor fruiting crops. They chose the stricter reading. The beds will be raised, 12 in deep, filled with purchased screened topsoil and compost, over landscape fabric so the fill stays separate from the yard soil. Their crop list (tomato, pepper, bush bean, lettuce, cucumber, basil) is mostly fruiting crops already; the lettuce goes in the clean fill, and they will remove outer leaves and wash it, as EPA's page advises for leafy crops. Paths between the beds get wood chips so no bare yard soil shows.
- Known: house built 1952; yard lead 140 ppm (fictional lab result); two children who play in the yard; the two tiers that 140 ppm falls in.
- Assumed: that the screened topsoil they ordered is "clean" in Cornell's sense, under 63 ppm. This is the Okafors' assumption, based on the supplier's description, not a measurement.
- Open: the delivered fill's actual lead and pH. The supplier settles it: the Okafors asked for the supplier's test results in writing before delivery, and if the supplier has none, they will sample the delivered pile and send it to the same lab. Also open: what 140 ppm in the play area means for the children. The county health department and the children's pediatrician settle that, and the Okafors have asked both. Until they hear back, the children play on the grass, not in bare soil.
Plot 14: clay, a high pH and a sand suggestion. Dale Whitcomb and Ruth Asante share a 10 x 20 ft community garden plot (200 sq ft) in heavy clay. The garden association's soil test (fictional) reports pH 7.4 and lead under 63 ppm.
Dale proposed buying sand to loosen the clay. Ruth ran a jar test first. After 48 hours her jar showed 1.0 in of sand, 1.2 in of silt and 1.8 in of clay, 4.0 in in total: 25 percent sand, 30 percent silt, 45 percent clay. On the texture triangle that is a clay. Oregon State's EC 1561 settles the sand question: sand in clay can set like concrete, and no amount changes the texture class. They dropped the sand.
Instead they will spread 1 in of compost over the plot. EC 1561 gives the volume directly: 0.6 cubic yards for 200 square feet. On pH, 7.4 is above Nebraska G945's 6.5 ideal but below the 7.5 where G945 says change is often necessary, and within EPA's 6.5 to 7.5 near-neutral range. Lowering pH with sulfur is slow and, by G945's account, often impractical. They will not add sulfur on their own judgment.
- Known: pH 7.4 and lead under 63 ppm (association test, fictional); 200 sq ft; their jar test result, about 45 percent clay.
- Assumed: that the association's sample represents plot 14. Dale and Ruth assume this; they do not know how many plots the composite covered.
- Open: whether the lab's written recommendations call for any pH change for vegetables. Only the lab's recommendation page settles that, and the garden coordinator holds it; Ruth asked the coordinator for a copy of the full report, including the sampling notes.
Free demonstrations
- Soil Lead Screening: Understanding Your Results and Next Steps (New York Soil Health, Cornell): the full tier table and testing methods compared, on two pages. It is dated November 2024 and describes EPA's January 2024 cleanup guidance, which EPA's October 2025 directive has since superseded.
- Residential Soil Lead Directive for CERCLA Sites and RCRA Hazardous Waste Cleanup Facilities (U.S. EPA): the October 2025 cleanup directive. It sets a 200 ppm screening level for cleanup programs and says nothing about gardening.
- Healthy Gardening Practices to Reduce Exposure to Lead-Contaminated Soil (U.S. EPA): exposure routes, everyday practices and EPA's three tiers in the agency's own words.
- Soil Texture Analysis: The Jar Test (Clemson HGIC 1656): photos of the layers settling at each reading time.
- Sampling Instructions for Routine Soil Analysis (UMass Amherst): one lab's complete sampling and submission steps, including what each optional test measures.
7. Practice Practice
Minimum: Call 811, map the area, take and send one sample, and read the report when it arrives; skip the jar test and the soil record sheets. Bagged mix in containers needs no sample. Time: about 1 hour of work, spread over three days (sampling and the jar setup on day one, drying overnight, the last jar reading 48 hours later), plus the lab's turnaround. Materials: a clean bucket, a trowel or spade, a ruler, a straight-sided clear jar with a lid, a sieve or colander, a marker, sheets of newspaper or paper, zip-top bags, and the lab's submission form.
- Call 811 if you will dig. The Common Ground Alliance's 811 Before You Dig service is free, counts planting a garden as digging, and notes that some lines are buried only inches deep. Contact it a few business days ahead.
- Map the areas. Sketch the yard or plot. Mark each area that looks or has been treated differently, and anything from the lead list: an old painted wall, a road, a former building, fill. Give each area a short name.
- Pick the lab and read its instructions. Find your state's lab through extension. Note its subsample count, depth, drying and shipping rules. Ask whether lead is in the routine test. If containers of bagged mix are your only plan, skip the rest of this practice and go on to Module 4.
- Collect the subsamples. For one area, take the lab's number of scoops from random spots, to the lab's depth, avoiding edges. Put them in the clean bucket. Do not sample within 6 to 8 weeks after lime or fertilizer, or when the soil is soaking wet.
- Mix and dry. Break up clods, remove stones and roots, mix well, and spread about a cup on paper to air-dry overnight without heat. Bag it, label it with the area name, and fill in the form, including the crop (vegetable garden).
- Go deeper Start a jar test with some of the leftover mixed soil, following Clemson's steps. Mark the sand at 1 minute, the silt at 2 hours and the clay at 48 hours. Record the three heights, the percentages and the texture class in the texture sheet.
- Go deeper Record the sample in the soil test sheet: lab, date sampled, depth, number of subsamples, and status "sent."
- When results arrive, copy every value with its unit and the recommendations word for word. Read them in the order given in the report section. If lead was tested, find its row in the tier table, and write down which questions go to the health department.
8. Your garden Your garden
9. Check your work Check your work
Criteria
- Did each sample come from one area of similar soil, with the lab's subsample count and depth?
- Was the sample air-dried without heat, and taken at least 6 to 8 weeks after any lime or fertilizer?
- Did you confirm whether lead is in the lab's routine test, and add it where the lead list applies?
- Are results recorded exactly as printed, with units, and recommendations copied word for word?
- Is the jar test recorded as an estimate, with the three heights as well as the percentages?
- If lead was tested, can you name the EPA tier and the Cornell tier your result falls in, and who you will ask about health?
Worked example
The Okafors (fictional) meet the criteria for the yard: one composite sample from the area where the beds will go, lead added because of the 1952 house, the result recorded as "140 ppm (mg/kg)," both tiers named, and the health question sent to the health department and the pediatrician. One gap remains, and they have recorded it as open rather than assumed away: the fill has not been tested. Their soil record shows the yard test as "confirmed" and the fill as "unresolved" until the supplier's results arrive.
Plot 14 (fictional) meets the jar-test criterion and records its estimate correctly, with the heights. It does not yet meet the report criterion, because Dale and Ruth have the association's numbers but not its written recommendations. Their record says so.
Common mistakes
- One spadeful from one spot. A single scoop reports that spot. Count your subsamples against the lab's number.
- Mixing areas. Soil from the house foundation and the back lawn in one bag averages away exactly the difference that matters for lead. Bag them separately.
- Sampling right after fertilizing. If you spread fertilizer or lime in the last 6 to 8 weeks, wait.
- Oven-drying a wet sample to mail it faster. Air-dry it.
- Liming because the neighbors do. pH varies by site. Apply lime or sulfur only from a recommendation for your sample.
- Comparing numbers across labs. A phosphorus value from one extraction method does not compare with a chart for another.
- Reading the jar test to the percent. It is an estimate. Write the class in words.
- Treating a garden tier as a health answer. The tier says where to grow. The health department or physician answers health questions.
What is still unresolved
This module cannot tell you what to add to your soil or how much. The lab's recommendation does, and Module 9 converts it into a product amount. It cannot tell you whether a lead result is a health concern for anyone in your household; your health department or physician answers that. It cannot settle whether purchased fill is clean; the supplier's test results, or your own sample of the delivered fill, settle that, and Module 4 covers buying fill. And one test describes one moment: Nebraska's G945 suggests retesting about every fifth year, or sooner after a major amendment.