Soil Testing : Master Gardener Association of San Diego County

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Soil Testing for Healthy Soil

Soil is more than dirt - it’s a living, dynamic resource that sustains plant life by providing nutrients, water, air, and a home for countless organisms. Its texture, structure, and composition influence everything from drainage and nutrient storage to plant health and resilience. Understanding your soil type, pH, and structure helps you choose the right plants and amendments for optimal growth. With the right care - such as adding organic matter, improving drainage, and avoiding compaction - any soil can be enhanced to support a productive, beautiful garden, “Have Your Soil Tested. Soil Management,” UCCE Master Gardeners of Orange County. (http://mgorange.ucanr.edu/Soils-Fertilizers-Compost/?uid=1&ds=547)

Soil testing can aid in improved soil quality by informing how and when to amend soils for the specific type of home gardening and landscaping
Testing aids in planting the right plant in the right place which will promote healthy plant growth
Testing aids in proper use of fertilizers. Often fertilizers are overused, which can impact the environment.

17 nutrients are needed for healthy plant growth

Drawn from air and/or water: carbon, hydrogen and oxygen,
Drawn from soil: Primary nutrients (nitrogen (N), potassium (K), and phosphorous (P); secondary nutrients (calcium, magnesium and sulfur); Micronutrients (boron, chlorine, copper, iron, manganese, molybdenum, nickel and zinc),
Nutrient imbalance (excess or deficiency) can result in poor plant growth.

pH- Alkalinity or Acidity of Soil

Soil pH determines the availability of the soil nutrients,
Most crops do best in pH range of 5.5-7.5, however, this information is often available for the plant type. Ideally, place plants in locations where pH is compatible.

When to Consider Soil Testing

If establishing a new garden or landscape.
If plants show poor growth. Often visual symptoms are difficult to diagnose due to overlapping deficiencies and variable symptoms depending on the plant type.
Timing: The best time for soil testing is in the fall. This allows adequate time for correction of nutrient deficiencies before spring planting.

Soil Testing Options – Home Kits vs. Commercial Laboratories

Home kits available at garden centers: Test for pH, nitrogen (N), phosphorous (P) and potassium (K).

Pros - quick and inexpensive especially for small gardens; Cons - accuracy varies, kits may be more suitable for eastern gardens with acidic soil and not the alkaline saline soils of California.
Home kits can also be ordered at

San Diego Seed Company – Verified Feb 2026

Website: https://sandiegoseedcompany.com/product/tools-and-merchandise/laboratory-soil-testing/

Commercial labs are more accurate than home kits. Labs can offer a broader range of testing, and often have a standard testing panel that may include macronutrients, nitrogen (N), phosphorous (P), potassium (K), calcium, magnesium, sulfur and micronutrients boron and zinc; pH, sodium, concentration of soluble salts and organic matter. Some include trace minerals such as aluminum, arsenic, cadmium and lead.

Pros - good for large gardens or landscaping projects, testing more extensive and often includes interpretation with recommendations.
Cons - cost varies but can be more costly and gardener is responsible for collecting and submitting the samples (usually via mail).
Call or visit each lab website for information.

How to take samples: Always consult the testing laboratory website for specifics on sampling and submitting sample before you begin. Correct sampling is key to an accurate test. Test results are only as good as the sample submitted.

Other Considerations

Important to remember that soil which has all the needed nutrients will not support healthy plant growth if irrigation water is of poor quality (high in salts, chloride, sodium or boron) or water management is poor (over or under watering).