University of Hawaiʻi at Mānoa Agricultural Diagnostic Service Center

This lab uses:

• Phosphorus: Mehlich-3 or Olsen, depending on the soil. Used across much of the East, South and Midwest, on acid to neutral soils. Sodium bicarbonate. Made for alkaline, high-lime soils like most of the West.

Using different tests for different nutrients is normal. The soil test calculator lets you pick the test for each one.

Labs pull nutrients out of soil with different chemicals, and each one gives a different number for the same soil. 20 ppm on one test and 20 ppm on another don’t mean the same thing, so check which test your report used before you compare it to a chart.

• Basic test. pH, phosphorus and potassium, usually with calcium and magnesium. Enough for most gardens and lawns.
• Organic matter. How much organic matter the soil holds, which sets how much nitrogen it releases.
• Nitrate. Nitrate nitrogen in the soil now. Most useful in dry climates, where it carries over winter.
• Salts. Soluble salts (EC), and sodium where salt or poor drainage is a problem.
• Micronutrients. Zinc, iron, manganese and copper, sometimes boron.

• The lab picks Mehlich-3 or Olsen for phosphorus based on the soil's pH, so check your report for which one it used.
• Pay by card online before you drop the sample off. No cash or checks.
• On Oʻahu, drop samples at Sherman Lab after calling ahead. On the other islands, drop them at the nearest CARES station.

Sources: [1] [2]

The lab’s site doesn’t say whether it takes samples from other states. Ask before sending one.

• Take 10 or more small cores across the area and mix them in a clean bucket. One spot tells you about one spot.
• Sample gardens and lawns about 6 inches deep, below any mulch or thatch.
• Keep beds that are grown differently, like a lawn and a vegetable garden, as separate samples.
• Wait a couple of months after fertilizing or liming, so the test reads the soil and not the last bag.
• Use the same lab and the same tests each time, so the numbers compare from year to year.

Your county Hawaii Extension office can help you take the sample and read the report.

Once the report comes back, type the numbers into the soil test calculator to see what to add for your bed or lawn. The soil test guide walks through each line of the report.

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