Perry Laboratory


Soil Testing

The objective of soil testing is to create a soil environment that will allow plants to grow their best. Proper soil nutrition ultimately leads to more beautiful and productive plants and a reduced need of fertilizers and pesticides. A soil test will allow you to eliminate guessing when applying fertilizers, select more appropriate plants, and identify potential problem areas. Over-fertilization (even with organic fertilizers) can allow nutrients, such as nitrogen and phosphorus, to pollute our rivers, lakes, and ocean. Under fertilization will cause plants to grow more slowly and be more prone to diseases and pests.

The best time to sample your soil is before you begin your garden design or 4 to 6 weeks before installing your landscape or garden. The relative cost of a soil test is small when you consider how much you will spend at the nursery to obtain your landscape plants and soil amendments and the time you will spend maintaining your plants.

Testing situations

New Landscapes – Soil testing is especially important at new home sites. Areas that have been graded to the subsoil are often deficient in all nutrients, especially the micro nutrients.

Renovated landscapes – Established plantings can be revitalized by the addition of proper amendments. Existing gardens may have sufficient fertility levels and only require individual nutrients.

Vegetable gardens – identifying key nutrients that your soil may be lacking can increase productivity.

Problem planting areas – Testing can reveal chemical deficiencies or toxicities that may be affecting plant growth in certain areas.

Imported “top soil” – Locally available products may contain excessively high levels of salts from some compost sources.

Frequently Asked Questions

  1. What information will I receive from my soil test?
  2. How do I obtain a good soil sample?
  3. When is the best time of the year to sample my soil?
  4. Can I have organic fertilizer recommendations?
  5. If I have been adding manure and compost to my vegetable garden for years can I assume that the nutrient levels are adequate, making a soil test unnecessary?
  6. Might the results from the soil test influence the types of plants that I choose for my garden or landscape?
  7. Does the quality of my irrigation water have an effect on the soil and plant growth?
  8. How do I incorporate the recommended amendments into my soil?
  9. What is pH?
  10. Texture vs. Structure
  11. Can soil testing benefit my lawn?
  12. Can I over fertilize my soil? What problems will this cause?
  13. Will a soil test identify every problem with my soil?

Frequently Asked Questions

Q. What information will I receive from my soil test?

A. Depending on the package you choose, your soil report will include the chemical and/or physical analyses and general guidelines for the crop or plants you are growing, an interpretation of the results and, most importantly, a list of recommended amendments. The report is straight forward and easy to understand. You can take the list of amendments to your local nursery or garden center.

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Q. How do I obtain a good soil sample?

A. You will need a random composite sample, consisting of sub-samples, of the area in which you will be planting and managing in the same way. Obtain the sub-samples from 4 to 6 different locations. An easy way to obtain these is with a clean shovel. Dig an 8 to 12 inch deep hole and place the contents to the side then take a two inch slice out of the side of the hole. Discard the upper 2 inches of surface soil. Place this sub-sample in a clean bag or bucket and mix well with the other sub-samples that are representative of where you will be planting. Place 4 cups of your mixed soil into a zip-lock type bag and label it with an indelible marker. Include your name and address and where your sample is from i.e.: front yard, veggie garden, etc. For vineyard and orchards, obtain sub-samples from the 18 to 24 inch deep range. Specific problem areas should be sampled separately.

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Q. When is the best time of the year to sample my soil?

A. Sample as early in the growing season as possible. For vegetable gardens and annual flowerbeds, sample in late winter or early spring. For fall plantings of perennials and cool season vegetables, sample in late summer. Send in samples 4 to 6 weeks before installing your garden or landscaping to allow for proper plant selection and acquisition of planting amendments.

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Q. Can I have organic fertilizer recommendations?

A. Of course. Please specify that you would like organic instead of conventional fertilizer recommendations when you send in or drop off your sample. One thing to remember with organic fertilizers is that they have a lower nutrient analysis than their chemical counterparts so you will need a larger amount to achieve the same results. For example, if your soil is deficient in phosphorous and you need to add 25 lbs of phosphorous per 1000 square feet of planting area, you will need about 55 lbs of Superphosphate (46% P2O5). You will need about 225 lbs of bone meal (11% P2O5) to provide your plants with an equal amount of phosphorous.

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Q. If I have been adding manure and compost to my vegetable garden for years can I assume that the nutrient levels are adequate, making a soil test unnecessary?

A. Manures can add salts, which can build up over time and actually stress out your plants. At moderate levels, salts add fertility to the soil but at high levels they can become unbalanced and toxic. Plant roots have a more difficult time extracting water from the soil water when the Electrical Conductivity, a measure of total salt content, is above 4.0 dS/m or mmhos/cm. Mushroom compost, in particular, can have excessive potassium, sodium and chloride levels and should be regarded more as a fertilizer than a traditional compost. Unlike compost, it is a poor choice for the addition of organic matter because it will reduce its volume by about half within a year because it is still in a state of decomposition. If you choose to use mushroom compost, use no more than a one inch layer and make sure that it is well mixed into the soil. Also, do not use it as a potting soil. Many gardening books recommend the use of wood ashes to supply potassium. Too much ash can elevate soil alkalinity and potassium levels and actually stress out the plants.

Well-aged compost is a wonderful amendment that will buffer the soil pH, improve structure, water penetration, moisture holding capacity, and microbial activity but doesn’t have high fertility. As with most things, moderation is the key. A soil test may reveal that after years of adding compost and manure to your garden, you may only need to add one or two individual nutrients.

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Q. Might the results from the soil test influence the types of plants that I choose for my garden or landscape?

A. Yes. If you are planting a large area it may be more realistic to choose plants that will be competitive in your native soil than to add large amounts of amendments. For example, it would be easier to plant drought resistant plants in sandy soils, acid-loving plants in the more acidic soils of the mountains, or salt tolerant plants in saltier soils. The primary toxic salts are sodium chloride, sulfate, and boron.

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Q. Does the quality of my irrigation water have an effect on the soil and plant growth?

A. Generally, city water is suitable for irrigation. Some untreated well waters, however, can have high levels of salts and bicarbonates. Over time, the accumulation of salts from irrigation water can impact the plant’s ability to uptake water and nutrients from the soil. Plants vary in their ability to tolerate salt buildup. Roses and bamboo are intolerant to high salt levels while rosemary and oleander are more tolerant. Irrigating with alkaline water containing high levels of bicarbonates can increase soil pH to ranges undesirable to some plants. Water with high levels of calcium and magnesium, commonly known as hard water, will leave unsightly white spots on plant leaves when used for overhead irrigation. Most soils can be managed to accommodate poor quality irrigation water. Local well water may also contain toxic levels of boron and sodium chloride from seawater intrusion near the coast. Areas in the Santa Cruz Mountains also have pockets of salty ground water. It is essential to know the chemical makeup of water that is used in fertigation (liquid fertilizer) programs. Collect irrigation water samples in a clean one-liter bottle and fill to the top.

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Q. How do I incorporate the recommended amendments into my soil?

A. If you are planting a new landscape or garden, work the amendments evenly into the soil as deep as realistically possible. If you are amending an already established landscape, add the amendments to the soil around base or drip line of the plant. You can mix it into the top few inches of soil in the root zone underneath the foliage or place it on top of the soil and cover with mulch. This method of top dressing will take a little longer to get the nutrients to the plant roots. Spreading out the amendment well will allow more roots near the surface to benefit from the fertilizer. If you are planting an orchard or vineyard, the amendments are to be added to the backfill soil mixture. Always water thoroughly after fertilizing to allow water to dissolve and transport nutrients down into the soil. Soil microorganisms need moisture to break down organic amendments and make the nutrients available to the plants’ roots. It may take several years for lime to increase the pH of acid soils. So it is better to begin the process sooner than later.

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Q. What is pH?

A. pH is known as the master variable of the soil because it controls the availability of plant nutrients. It is a measure of the soil acidity or alkalinity. A pH of 7 is neutral and less than seven is acid and above 7 is basic or alkaline. Most plants prefer to grow in a slightly acidic to slightly alkaline soil of pH 6.5 to 7.2. As pH increases, becomes more alkaline, phosphorous, iron, manganese, boron, copper and zinc become less available or more “tied-up”. As pH decreases, or becomes more acid, phosphorous, potassium, sulfur, calcium, magnesium, and molybdenum become less available. At very low pH levels aluminum and iron become available in toxic quantities. Soils become more acid when ammonium nitrogen fertilizers are applied and when the cations calcium, magnesium, and potassium are leached from the topsoil into the subsoil. This explains why many soils in the Santa Cruz Mountains are acidic.

A soil’s pH can be increased by the addition of lime. It can be decreased by the addition of acidifying materials such as sulfur, iron sulfate, ammonium sulfate, or peat moss. All amendments need to be well mixed and watered into the soil. Soil texture will determine the appropriate rate of liming or acidifying material.

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Q. Texture vs. Structure

A. Texture is the measure of the relative proportions of soil particle sizes, which are divided into three categories; sand, silt and clay. The ideal garden soil is a loam, which contains nearly equal amounts of sand, silt, and clay particles. Both sandy and fine textured clay soils have advantages and drawbacks and require different management practices. Clay soils, also called heavy or fine-textured soils, are more susceptible to compaction and require higher levels of amendments, yet have a higher capacity to retain both water and nutrients. Sandy soils hold less water and fewer nutrients and are more susceptible to leaching, yet are not as prone to compaction and water-logging. Be careful not to over fertilize on sandy soils especially if you live near a creek or drainage course.

You cannot realistically change your soil’s texture. The volume of sand needed to change a clay soil to a loam would be prohibitive and likely turn your soil into adobe brick during the summer. The addition of large amounts of organic matter will improve heavier soils rather than the addition or sand to change the soil’s texture. Sandy soils like those in Ben Lomond, Scotts Valley and some coastal areas may benefit from the addition of loam soil to small garden beds but would probably benefit more from the addition of organic matter especially considering the poor composition and quality of locally available “top soil”.

Texture is commonly confused with structure. Structure refers to the way that soil particles are grouped or aggregated together to create a system of large and small pores that allow the passage of air and water. A soil with good structure will maintain its shape when dry and crumble easily when moistened and handled. Structure can be improved by adding organic matter such as aged manure, compost, nitrified sawdust, rice hulls, peat moss, green manures, or straw. Organic amendments that have a high carbon to nitrogen ratio such as brown and dry materials like straw and sawdust will provide a greater benefit once they have decomposed. The addition of a nitrogen source such as ammonium sulfate at the rate of 2.5 lbs per cubic yard will speed up the decomposition of organic matter to a point where your plants can utilize it. Fresh manures should also have a chance to decompose in the soil before planting. Good structure can be maintained by avoiding compaction when the soil is wet. Soils that contain high levels of sodium (sodic soils) often are characterized by poor structure which leads to poor drainage characteristics and can be remedied by the addition of gypsum (calcium sulfate). Although sodic soils are unlikely to be found in our area because of the high rainfall, sodium can build up in soils when irrigated with water that is high in sodium.

Soil development is influenced by parent material, climate, vegetation, aspect (southern vs. northern exposure), topography, and time. Due to variable topography with our mountains, foothill, river beds, ancient sand dunes, soils can vary considerably within a region or even a neighborhood.

The USDA’s Soil Survey catalogs and describes the local soils and their uses and limitations. To view the Santa Cruz County Soil Survey online go to The Natural Resources Conservation Service.

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Q. Can soil testing benefit my lawn?

A. The use of cheap nitrogen fertilizers like ammonium sulfate to green up lawns can reduce pH levels and cause deficiencies of calcium and phosphorous. These deficiencies and imbalances will manifest in less vigorous growth and less resistance to disease and wear.

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Q. Can I over fertilize my soil? What problems will this cause?

A. The improper use of fertilizers, even organic ones, can upset the chemistry of the soil causing toxicities and chemical imbalances. Over-fertilization is not only a waste of money but also a source of pollution. Nitrogen compounds are easily leached from soil by heavy irrigation and rain. They degrade our water supplies and are harmful to aquatic life. Sandy soils are especially susceptible to leaching and benefit from smaller and more frequent additions of fertilizers.

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Q. Will a soil test identify every problem with my soil?

A. Poor plant performance may result from non-fertility related problems such as poor drainage and lack of sunlight. Soils affected by poor drainage and extended periods of saturation (water logging) are often characterized by red and gray mottles. Some plants cannot tolerate overly wet conditions. Poor growth can also be attributed to a lack of sunlight. Many plants need a full day of sun to fully mature and flourish. The staff at your local nursery should be able to assist you in selecting appropriate plants for shadier and wetter areas.

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Sending your sample to the Laboratory

Samples can be sent by US mail, UPS, FedEx or any other carrier to:

  • Perry Laboratory
  • 424 Airoprt Boulevard
  • Watsonville CA 95076

Samples may also be dropped off at the same location. The lab is open from 9 to 5 pm Monday – Friday.

Plant tissue sampling guide

Please submit payment along with the sample(s).

Horticultural Sample Submission Form

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Testing Packages

H-1-R Landscape Appraisal Package with Recommendations
For installing or remodeling a landscape. Includes all chemical analyses plus texture, organic matter, and lime. This is the package used by the more experienced landscapers and landscape designers. $235.00
OM-1-R Organic Media Package with Recommendations
For evaluating an organic media for plant growth. Includes all chemical analyses plus physical properties and nutrient holding capacity. This is the package used to help determine the suitability of an organic growing medium for growing different plants. $270.00
S-14-R Fertility and Minor Elements with Recommendations
For monitoring a landscape or vegetable garden to maintain or improve growth. Includes pH, electrical conductivity, nitrate nitrogen, ammonia nitrogen, phosphorous, potassium, calcium, magnesium, sulfate, boron, zinc, copper, manganese and iron. $117.00
S-2-R Fertility-Salinity-Alkalinity Appraisal with Recommendations
For the diagnosis of a soil in a problem area. Includes fertility plus saturation percentage, calcium plus magnesium, sodium, chloride, boron, SAR, ESP. $120.00
S-1-R Fertility Analysis with Recommendations
Follow up testing with emphasis on major nutrients. Includes pH, electrical conductivity, nitrate nitrogen, ammonia nitrogen, phosphorous, potassium, calcium, and magnesium. $72.00
W-1-R Well Water used for irrigation with Recommendations $140.00
SP-4 Soil Texture $47.00

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Other Services

  • Petiole analysis for vineyards (please call to request a brochure)
  • Fertigation (liquid fertilizer) water analysis
  • Plant tissue analysis.
  • Potting soil analysis

Please include the following information with your sample(s):

  1. Name
  2. Address and phone number
  3. Email Address
  4. Planting Situation i.e.- established/new garden, new home site
  5. Sample ID
  6. Conventional or organic fertilizer recommendations
  7. Additional information about sample

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Perry Laboratory - Serving Horticultural Industries since 1938