Garden Soil Testing: Sampling, Results & Soil Lead Chart

On this page: Taking a sample · Where to send it · Reading the results · Soil lead chart · Gardening on soil with lead · Where sources differ

At a glance

Question	Short answer
When to sample	Fall or early spring, any time the soil is not frozen, very wet or very dry (Iowa State); keep the timing the same from year to year (MU)
How often	Every 3 to 5 years, or sooner if plants struggle (Iowa State)
Cores per sample	At least 10 for a garden or lawn up to 10,000 sq ft (Illinois, UVM)
Depth in a garden bed	Tillage depth, usually 6 to 10 inches (Illinois, UVM)
How much to send	About 1 to 2 cups of the mixed soil (Illinois, UVM)
Basic test	Phosphorus, potassium, pH and organic matter; lead is often an add-on (Iowa State)
Turnaround	Typically one to two weeks (Iowa State)

Taking a sample, step by step

Pick one uniform area per sample. Do not mix lawn soil with vegetable-garden soil; sample a struggling patch separately from a healthy one (Illinois). Vegetable gardens and children's play areas are sampled separately for lead too (UMD).
Sample before amending. Take samples before lime, fertilizer or manure go on (UVM), and not right after compost (Iowa State). Skip odd spots such as places where fertilizer or lime was spilled (UVM).
Use clean tools. A soil probe is best; a trowel or spade works if you cut a slice about ½ inch thick and trim it to a 1-inch strip (Illinois, UVM). Collect into a clean plastic bucket, since metal buckets may contaminate the sample (MU).
Walk a zigzag. Take cores at random spots along a zigzag across the area, all to the same depth (Illinois). Iowa State suggests 10 to 15 spots; MU, 15 to 20.
Leave out the surface litter. Remove mulch, compost, roots and vegetation from each core (Illinois, Iowa State).
Mix, dry and bag. Mix the cores thoroughly (UVM), air-dry a wet sample at room temperature, never in an oven (MU), and put about 1 to 2 cups in a plastic bag or the lab's bag, labeled with your name, the date and the area (Illinois).
Check the lab's form first. Ask about cost, shipping and whether it tests for contaminants (Illinois), and follow its sample-size and labeling instructions (Iowa State).

Drawing by The More One Sows, based on the cited sources. Not to scale; core depths follow the inch scale at left.

1. Garden bed: 10 or more cores along a zigzag, one sample for the whole bed (Illinois, UVM)
2. Lawn: a separate sample, never mixed with garden soil (Illinois)
3. Play area: sampled separately when testing for lead (UMD, UMass)
4. Garden core: 6 to 10 inches, the tillage depth (Illinois, UVM)
5. Lawn core: 4 to 6 inches (Illinois, UVM)
6. Play-area lead sample: top 1 to 2 inches, where lead is highest (UMass, UMD)
7. Clean plastic bucket for mixing, not metal (MU)
8. About 1 to 2 cups of the mix, bagged and labeled (Illinois, UVM)
9. Mulch, compost and roots trimmed off each core (Illinois, Iowa State)

Where to send it

Your county extension office can help interpret pH and nutrient results and can point to local labs that test for contaminants (EPA). Not every state university runs a lab: Iowa State, for example, does not test soil and refers gardeners to university labs in Minnesota and Wisconsin or to private labs. Whatever the lab, choose one that gives recommendations for home lawns and vegetable gardens, because field-crop reports do not apply to a home garden (Iowa State).

Option	What to know
Land-grant university lab	Several land-grant universities house a soil lab, among them Missouri, Wisconsin, Kentucky, Minnesota and Kansas State (Illinois). Delaware and UMass include lead in the basic home test, and Penn State lists it under environmental soil testing (UMD).
Private lab	Illinois Extension advises labs certified by the Agricultural Laboratory Testing Association, whose directory lists each lab's services.
Home test kit	Usually only nitrogen, phosphorus, potassium and pH, with vague or color-matched results; Iowa State calls kits inferior to lab tests. Home lead kits are screening only, with a wide range of accuracy (NYSH).
XRF reading	A quick lead screen by a trained professional, moderately accurate and affected by soil conditions; confirm high readings with a certified or university lab (NYSH).
Former industrial or commercial site	Test for contaminants suited to the site's history. A Phase I assessment reviews that history; a Phase II samples for contaminants. State environmental agencies and EPA's Technical Assistance to Brownfields program can help (EPA).

Basic tests usually report phosphorus, potassium, pH and organic matter. Add-ons include lead, soluble salts, calcium, magnesium, sulfur, boron and micronutrients; heavy metals and microbial tests cost extra (Iowa State). Illinois Extension recommends optional lead and heavy-metal testing in urban or developed areas, especially around homes built before the mid-1970s.

Reading the results

Line on the report	How to read it
Soil pH	Most vegetables do best at 5.5 to 7.0; blueberries at 4.5 to 5.5. Phosphorus is tied up below pH 6.0 or above 7.3 (UMD).
Buffer pH	Stored acidity: the lower it is, the more lime the soil needs to raise its pH (UMD).
Phosphorus, potassium ratings	Low or very low: fertilizer will likely increase growth. Medium: a response may or may not occur. High or very high: more fertilizer will probably not help (Mississippi State). Do not add phosphorus at medium to high levels (UMD).
Organic matter	Healthy soils have 2% or more; because it is measured by weight, a well-amended garden can still read under 5% (UMD).
CEC	Under 10, add organic matter (UMD).
Nitrogen	Not measured; recommendations are based on research (Mississippi State).
Lime and fertilizer	Usually given in pounds per 1,000 sq ft (UMD, Mississippi State). Apply lime before fertilizer, ideally about two months ahead (Mississippi State).

To scale a recommendation, divide pounds per acre by 43.56 for pounds per 1,000 sq ft, or by 435.6 for pounds per 100 sq ft (UMD). For a fertilizer, divide the recommended nitrogen by the product's nitrogen fraction: 3 lb of nitrogen per 1,000 sq ft from a 13-13-13 is 3 ÷ 0.13, or 23 lb (Mississippi State). Then scale by area: a 100 sq ft bed needs one-tenth of a per-1,000 sq ft amount (Mississippi State). Measure the bed's length and width as for the raised bed soil calculator.

Soil lead chart: what each level means for a food garden

Lead results come in ppm, the same as mg/kg (NYSH). Look for the total lead value: a report may list an extracted test, a total test or both (UMD). UMass's routine test uses a mild extraction that only flags possible problems; it recommends its total test for gardens and play areas. No legal limit for garden soil lead is in effect (UMD), so the bands below are guidance and differ by source.

Total soil lead	What the sources advise
Under 63 ppm	Typical background; no extra precautions or crop limits (NYSH). Maryland puts natural background under 50 ppm, UMass at 15 to 40 ppm.
63–99 ppm	Above background: use more amendments and barriers; consider not growing root crops (NYSH).
100–199 ppm	Suggests contamination: raised beds with clean soil; consider skipping leafy greens and root crops and focusing on fruiting crops (NYSH). UMass rates 100–400 ppm as potential risk, managed with good gardening practices.
200–399 ppm	Grow only in raised beds with clean soil and keep other soil covered (NYSH). EPA uses 200 ppm as its residential screening level at Superfund and RCRA cleanup sites.
400–999 ppm	No leafy greens or root crops in the ground; raised beds with clean soil; dense cover to keep children off (UMass). NYSH notes that EPA designates 400–1,200 ppm a soil lead hazard for bare soil in residential and play areas, and EPA's removal management level at cleanup sites is 600 ppm. Maryland allows fruiting crops in the ground at 401–1,000 ppm, with greens and roots in containers or raised beds of at least 8 inches of clean soil and compost.
1,000–2,000 ppm	No food crops in the soil and no child access; keep it covered and grow in containers or lined raised beds (UMass).
Over 2,000 ppm	Contact the local health department, extension or state environmental agency for abatement advice (UMass). Above 5,000 ppm next to a home, Maryland says to consider removal by a certified contractor.

Gardening on soil with lead

Lead comes mainly from old lead paint, past leaded gasoline and old lead arsenate orchard sprays (UMass), as well as industry and traffic near roads (EPA). It builds up in the top 8 inches and is largely immobile (UMD); it persists for hundreds of years, often concentrated near its source (UMass). Plant uptake is low; the main risk is swallowing soil and dust, and leafy greens and root crops carry more lead than tomatoes, peppers or cucumbers (UMD). Carrots readily take up lead and store it in the edible root (UMD), which matters for a carrot bed.

Build up, not down. Raised beds or containers with landscape fabric under clean soil, framed with untreated lumber (EPA); avoid railroad ties, telephone poles and treated or painted wood (NYSH). For pots, see container sizes and the garden types overview.
Add organic matter. Compost mixed in up to 50:50 by volume dilutes contaminants, and phosphate and compost can reduce lead's bioavailability (EPA); Maryland adds phosphorus as the soil test recommends.
Keep pH near neutral. 6.0 to 7.0 (UMD); UMass limes to 6.5 to 7.0.
Cover bare soil. Mulch beds and paths to cut dust and splash (EPA, NYSH).
Wash up. Wear gloves, wash hands after gardening, leave shoes at the door, wash produce, peel root crops and discard the outer leaves of greens (EPA, UMD).
Favor fruiting crops. Tomatoes, squash and berries are generally most suitable, root crops least (EPA); see tomatoes.

This page is not medical advice. Maryland Extension advises parents of children under 6 in areas with lead-contaminated soil to consult a physician, who may recommend a blood lead test.

Where sources differ

Point	What each source says
Garden sampling depth	6–10 in (Illinois, UVM); top 4–8 in (Iowa State); 0–6 in (MU); 6–8 in for lead (UMass)
Cores per sample	10 minimum (Illinois, UVM); 10–15 (Iowa State); 15–20 (MU)
Amount to send	1–2 cups (Illinois); about 1 cup (UVM); about 1 pint (MU)
Retesting	Every 3–5 years (Iowa State); every 2–3 years for fertility in crop systems (MU)
Target pH with lead	6.0–7.0 (UMD); 6.5–7.0 (UMass, NYSH)

Sources

All sources were opened and checked in October 2026. Rules and figures change; confirm with the original before acting.

Soil testing for small gardens: sampling, labs, results and lead