Why soil tests matter: lessons from my vegetable garden

Regular blog readers will remember that we moved to my childhood home a few years ago. With an acre or so of landscape I finally have enough room to put in a vegetable garden. My husband built a wonderful raised bed system, complete with critter fencing, and we’ve been enjoying the fresh greens and the first few tomatoes of the season.

Jim puts on the finishing touches to our first raised bed garden.

We filled these raised beds with native soil. During a porch addition I asked the contractor to stockpile the topsoil near the raised beds. The house was built almost 100 years ago and at that time there were no “designed topsoils” (thank goodness) – soil was simply moved around during construction. Some of this soil had been covered by pavers and the rest had been covered with turf. [You can read more about designed topsoils in this publication under “choosing soil for raised beds.”] There had been no addition of nutrients for at least 7 years so I was confident that this was about as natural a soil as I could expect.

Our native soil, ready for adding to our raised beds.

I’ve always advised gardeners to have a soil test done whenever they embark on a new garden or landscape project, so before I added anything to my raised beds I took samples and sent them to the soil testing lab at University of Massachusetts at Amherst (my go-to lab as there are no longer any university labs in Washington State for the public to use).

What I already knew about our soil was that it’s a glacial till (in other words it’s full of rocks left behind by a receding glacier). The area is full of native Garry oak (Quercus garryana), some of which are centuries old. The soil is excessively drained, meaning it’s probably a sandy loam. And that’s about all I knew until my results came back.

Some of our massive, centuries old Garry oaks.

Because nothing has been added to this soil for several years, and because I had removed all of the turf grass before filling the beds, I assumed that the organic matter (OM) would be quite low. Most soils that support tree growth have around 3-7% OM. Hah! Ours was over 12%! All I can figure is that centuries of leaf litter has created a rich organic soil.

I never expected this level of OM.

So here’s lesson number one: Don’t add OM just because you think you need it. Too much OM creates overly rich conditions that can reduce the natural protective chemicals in vegetation. This means pests and diseases are more likely to be problems.

I think these may be the lowest P levels I’ve seen in home garden soils.

I was pleased to see our P level was low. First soil test I’ve ever seen in my area where P was below the desirable range! Does that mean I’m adding P? No – because there is no evidence of a P deficiency anywhere in the landscape. And my garden plants are growing just fine without it.

No sign of any nutrient deficiencies here (though the mesclun mix got out of control).
Or here either.

 

 

 

 

 

 

 

 

 

 

Lesson number two: Just because a nutrient is reportedly deficient, look for evidence of that deficiency before you add it. It’s a lot easier to add something than it is to remove it.

Likewise, our other nutrient values are just fine, and I was pleased to see that lead levels were low. Given that this is an older house that had lead paint at one time, and given the fact that the soil being tested was adjacent to the house, I was prepared for lead problems.

Surprisingly low lead given the original location of this soil next to an older house.

However – we do have high aluminum in the soil. Exactly why…I don’t know. Perhaps the soil is naturally high in aluminum? There’s no evidence that aluminum sulfate or another amendment was ever used. In any case, that was an unexpected result that does give us some concern for root crops. I’ll be doing some research to see what vegetables accumulate aluminum.

The aluminum levels may bear some watching if I’m growing root crops.

Finally, note our pH – 4.9! This is completely normal for our area, which is naturally acidic. In addition, the tannic acid accumulation from centuries of oak leaves has undoubtedly pushed the pH even lower. Are we going to adjust it? Again, no. There is no evidence of any plant problems, and even our lawn is green. Why would we adjust the pH if there is no visual evidence to support that?

No, this is not a typo.

Which leads to lesson number three: Don’t adjust your soil pH just because you think you should. If your plants are growing well, the pH is fine. Plants and their associated root microbes are pretty well adapted to obtaining the necessary nutrients. If you have problems, don’t assume it’s a pH issue. Correlation does not equal causation! You’ll need to eliminate all other possibilities before attempting to change your soil chemistry. And remember it is impossible to permanently change soil pH over the short term. Permanent pH changes require decades, if not centuries of annual inputs (like our oak leaves).

The cat agrees – no pH issue with this lawn.

Will I test my soil again? Probably not. I have the baseline report and since I don’t plan to add anything I don’t expect it to change much. If I had a nutrient toxicity I would retest until the level of that nutrient had decreased to normal levels. But with everything growing well, from lawn to vegetables to shrubs and trees, there really is nothing to be concerned about.

Viburnum plicatum (I think) is one of many established shrubs on the property.

Lesson number four: Unless you have something in your soil to worry about, don’t.

Professional Credentials and Gardening Expertise

This is the first post in a series in which we will explore the world of professional credentials and designations, highlight disciplines related to gardening with certification or licensing programs, and outline potential services professionals from each of those disciplines can provide to gardeners.

Professional designations are designed to help clients identify experts within specific disciplines. In upcoming posts I will highlight professional designations relevant to various aspects of gardening. Professional certifications, licensures, and credentials related to gardening include:

  • Board Certified Entomologist (BSE)
  • ISA Certified Arborist
  • Certified Crop Advisor (CCA) and Certified Professional Agronomist (CPAg)
  • Certified Horticulturalist (CH)
  • Certified Professional Forester (CPF)
  • Certified Professional Soil Scientist (CPSS)
  • Professional Landscape Architect (PLA)
  • Registered Consulting Arborist (RCA)

Before I highlight each of those professions and credentials in future posts, I want to first provide context and explain the purpose of professional certification and licensing.

A registered nurse checks a newborn’s reflexes. Photo by Jacob Sippel courtesy of the U.S. Navy.

Most of us encounter professional designations on a daily basis without noticing. For example, you’re likely familiar with credentials such as Certified Public Accountant (CPA), Registered Nurse (RN), or Doctor of Medicine (MD). Such credentials are often identified with postnominal letters in the form of an acronym listed after someone’s name in print. In some cases these postnominal letters indicate both an academic degree and a professional certification or licensure, such is the case with medical doctors (MD). In some disciplines the degree and designation can be separate. I’ll use myself as an example (not as a humble brag, but as a convenient example). My business card says “Colby Moorberg, PhD, CPSS”. The PhD refers to the highest academic degree earned (Doctor of Philosophy, PhD), while the CPSS refers to the Certified Professional Soil Scientist professional certification. There are countless professional designations in current use, each of which comes with postnominal acronyms. That alphabet soup can become confusing. Yet to further complicate the matter, details vary greatly from one professional designation to the next. Such differences include the type of professional designation, education requirements, qualifying exams, codes of ethics, continuing education requirements, professional experience, and designating bodies.

Types of Professional Designations

Professional designations can take the form of professional licenses or certifications. According to Knapp and Knapp (2002), licenses are granted by government agencies and are required for people to practice or engage in their profession. The process ensures that licensed individuals have met the minimum education and experience required to be competent in their field without risk to themselves or the public. For example, engineers and physicians are required by law to have a license issued by a state licensing board before they can practice in their respective profession. Such professional licenses are somewhat analogous to the requirement that people operating a motor vehicle have a driver’s license – it’s illegal to drive without one.

An arborist tends to trees at the US Capital. Photo courtesy of the Architect of the Capital.

Knapp and Knapp go on to contrast professional certifications from licensing by stating that certification is a voluntary process administered by an organization (not a government agency) to recognize individuals that have met predetermined qualifications or standards. Such certifications help establish the credibility of a professional within a specific discipline when a license is not required. Consider a certified public accountant (CPA). Many people might think twice about trusting an accountant with their finances or tax preparation if that accountant was not certified, even though a license is not required for someone acting as an accountant. Professional certifications are typically administered by professional societies, and are usually used in professions where the immediate health and safety of the general public is not impacted by a professional in the respective discipline.

Education Requirements

Education requirements are put in place in most certification or licensing programs to ensure that the professional has the knowledge base necessary to be successful in their field. Certification and licensing programs often require an associate’s or bachelor’s degree in a related major, but not always. For example, a Certified Professional Forester is required to have at least a bachelor’s degree in forestry or a related major (Society of American Foresters, 2019), while a ISA Certified Arborist could become certified without a college degree if such an individual meets additional professional experience requirements (International Society of Aboriculture, 2019). Licensing boards or certifying bodies typically have panels of professionals within a discipline that review college transcripts of those applying to become licensed or certified in order to ensure each person with a credential meet the program’s minimum education requirement.

Qualifying Exams

All licensing boards and most certification programs have an exam that someone must pass in order to become licensed or certified. Similar to degree requirements, such exams help ensure the professional has the minimum level or expertise necessary to be proficient in their field. In some cases, professionals must pass two exams, one when they start their professional career fresh out of college, and a second after they’ve worked professionally for 3-5 years.

A multiple choice answer card. Photo by Alberto G.

Code of Ethics

Many licensing and certification programs require licensees or certificants to abide by a professional code of ethics. This is a useful feature for clients (gardeners wishing to hire a professional) because it provides a mechanism to report a professional if they are acting unprofessional or unethically. Such codes of ethics are also useful to licensed or certified professionals because it gives them an “out”, should they be asked to do something unethical by a client or an employer.

Continuing Education

Most licensing and certification programs require a minimum number of documented hours (continuing education units, or CEUs) dedicated to staying up-to-date. These hours are documented and must be met within a 1-, 2-, or 3-year cycle. Such continuing education requirements benefit gardeners hoping to hire a professional, because it ensures that professional is staying current in their field and is learning the newest technologies and techniques. Programs that require professionals to abide by codes of ethics often require professional ethics training for each cycle as well.

Books. Photo by Abhi Sharma.

Professional Experience

Certification and licensing programs often have a minimum number or years of professional experience required in order to become certified or licensed. Usually during the period in which someone is gaining experience, they are working under the wing of someone fully licensed or certified. Such requirements help ensure that fully certified or licensed professionals have documented professional experience, and have had the opportunity to apply academic knowledge to real-world applications.

Soil scientists inspect soils in a Christmas tree farm in North Carolina. Photo by David Lindbo via SoilScience.info.

Designating Bodies

Professional certificates or licenses often vary by the group, organization, or licensing board that bestows the professional credential on an individual. In some cases there are competing organizations that offer competing certificates.

Summary

The primary way in which gardeners benefit from hiring certified or licensed experts in their fields is that professional credentials ensure a minimum knowledge and competency by the professional. In addition, these professionals are often bound by their respective professional codes of ethics. As the old adage goes, you get what you pay for. In the case of certified or licensed professionals, this often means it will cost you more for the services of a certified professional. As we explore the different professions and professional credential programs relevant to gardening in future posts, I will discuss gardening-related services that can be provided by each type of certified or licensed professional, and scenarios where spending the additional money to hire a certified professional might be worth the added cost. I hope this information enlightened you to professional designations, certifications, and licensing. Hopefully it will help start a conversation between you and gardening experts to determine how they might be of service to you.

Have you encountered certified or licensed professionals in the gardening world? Discuss your experience in the comments, or suggest certification or licensing programs I may have missed in my list above.

Disclosure: I am a Certified Professional Soil Scientist (CPSS), and I am a member of the Soil Science Society of America (SSSA) Soils Certifying Board which oversees the CPSS program.

References

Knapp, L., and J. Knapp. 2002. The Business of Certification: Creating and Sustaining a Successful Program. 2nd Revised edition edition. Association Management Press,U.S., Washington, D.C.
International Society of Arboriculture. 2019. Types of Credentials. International Society of Arboriculture. https://www.isa-arbor.com/Credentials/Which-Credential-is-Right-for-You (accessed 29 July 2019).
Society of American Foresters. 2019. Requirements. Society of American Foresters. https://www.eforester.org/Main/Certification_Education/Certified_Forester/Requirements/Main/Certification/Requirements.aspx?hkey=7eae8378-e92b-438e-aba9-93e713cb38cc (accessed 29 July 2019).