Soil compaction–the urban stress of death for shade trees

I was taught in horticulture school that the ideal soil is composed of 50% solids and 50% voids or spaces which are themselves composed of a variable amount of water from small amounts to as much as 25% water when the soil is at field capacity or the amount of water left in soil after gravity has pulled all the free water down in the profile. So the “ideal” soil always has 25% pore spaces or more depending on how much water is present. These conditions are vital for root growth since roots go through the chemical process of respiration which involves absorbing oxygen and giving off carbon dioxide. For gas exchange to happen in this ideal soil, spaces or voids are important, and necessary. A well-structured soil has micro aggregates (pea sized or smaller clumps of soil) in high concentrations which creates many of these spaces and is said to have high porosity.

Porosity in soil is created by the action of roots, fungi and soil fauna developing channels, micro-aggregates and incorporation of organic matter so that soil becomes highly “structured”.

Porosity – the amount and types of voids – is determined by two major factors: 1) The size and distribution of the soil particles; and 2), how those particles are arranged. Sand, silt, and clay particles can be arranged and formed into pathways that help move air and water. These paths are formed by past root channels and the movement of organisms like worms and insects. These channels are glued together by exudates from roots, bacteria and fungi. This organic, both living and dead, soil fraction also add and stabilizes porosity. All together, soil particles, plant residues and microorganisms create a fragile structure that adds more porosity than just the pores and voids created by spaces between the soil mineral particles.

Soil structure is physically crushed and destroyed by cars driving over this tree planting area. As the surface compacts, runoff increases, the soil holds less water and oxygen as a result tree roots die.

Structure and porosity can be physically destroyed or crushed. The soil can be squished by heavy equipment or constant foot traffic of animals, such as humans or horses, or others that constantly tread over the same soil. Compacted soil can be near the surface (the worst for trees since their roots are mostly near the surface), or lower down in the profile. A “plow pan” is actually a compacted zone at the depth of plow or ripping agricultural implements where soil structure is constantly destroyed at the same depth over and over. As soon as roots and worms create a new pathway and reinforce it with micro-aggregates and glues, it is destroyed again, creating a zone of loosened soil where the implement has traveled, but a zone immediately below what which has been compacted by the pressure of the implement.

Most horticulturists and many gardeners know that compacted soils are bad for plants growing in them. Shade trees frequently have restricted growth in these kinds of soils. This can happen at a young age when trees are just planted or on large specimen trees, such as in parks that have the soil compacted around them by visitors. Footpaths, picnic tables, playground equipment or any publicly attractive park feature will often have compacted soils in the area.

Deprivation of litterfall and mulch layers, either through wearing out (grinding of organic matter by foot traffic) of the mulch or by mulch/litter removal through raking will promote compaction by removing the cushioning effect of that mulch layer. Sadly, the tree itself can be the feature that attracts people to it, resulting in compacted soils all around its base that limits its health.

Tree growth is limited when soil is compacted around the trunk. Turf loss, and a dry soil are symptoms of a compacted zone around this tree

What is not so well known is why growth is slowed in compacted soils. The effects of compaction are multi-fold. Compacted soils are less porous because the compaction literally reduces the air pockets in the soil, making it more dense with lower oxygen diffusion rates. Soil with destroyed structure becomes less permeable to water infiltration and holds less water. Under these conditions tree roots may not be adequately hydrated, and cannot physically penetrate the highly compacted soil. Thus, they are not able to develop and expand and explore enough to supply the needs of the tree. Reduced soil oxygen, along with other site, soil, and tree variables such as water and nutrient uptake, are all reasons for restricted tree growth.

There is compelling evidence that different species of trees can exert greater pressure at their root tips to break through compacted soils. Different tree species also have different root architectures – finer, deeper, shallower, etc. Thus, there is a genetic factor in a tree’s ability to deal with this soil problem.

Soils are more or less compactable depending on their texture, structure and moisture status. Generally a dry soil is harder to compact that a moist one. Dry soils resist compaction (but still can be compacted) because the soil aggregates stiffen as they dry. Wet soils are easily compacted but people and machinery also easily sink in very wet soils. Waterlogged soils may or may not have structure, but the water in the pores, prevents further collapse of the soil structure. Soils that are moist (at field capacity) are just right for growing plants, and are also perfect for compacting and thus must be protected from compaction.

Soil compaction is measured by calculating what’s called bulk density (Bd). Bulk density is the weight of soil in a given volume, and is measured in grams/cubic centimeter. In order to measure bulk density a special soil sampling device called an “intact soil core sampler” is used. This device extracts a core of soil while preserving its structure. The volume of the sample is a constant. The soil sample is removed and dried to drive off all the water and then the weight of dry soil is divided by the known sample volume giving the bulk density.

Bulk densities vary depending on the soil texture (%Sand:Silt:Clay) and to a smaller extent on the organic matter content. Sands generally have very large particles, more pore spaces and lower bulk densities than silts, loams and clays which willhttps://i1.wp.com/www.deeproot.com/blog/wp-content/uploads/stories/2014/04/Soil-organic-matter-soil-texture-table1.png?resize=636%2C326

A Comparison of Root Limiting Bulk Density for Different Soil Types (NRCS 1998 in Dallas and Lewandowski, 2003)have the highest bulk densities. Thus compaction is determined by measuring both bulk density and soil texture. Generally, pure rock has a bulk density over 2.65 g/cc. Uncompacted sands may have bulk densities of 1.2-1.4, while loams and clays may have Bd from 1.5-1.8 g/cc. A sand may be compact at 1.4 but a clay may have a higher Bd of 1.5 and not be considered compacted. Organic soils can have Bd that are much lower – 0.02-.9 g/cc. Generally, soils (average of all textures) with bulk densities over 1.5 can be suspected to be compacted and will limit tree growth.

Bulk density for a given soil is not a fixed property, it can change depending on the history of what has happened to the soil. For instance, in an annual color bed or vegetable garden bed, the soil may be turned or tilled by the gardener, amended, and replanted. During this process structure is destroyed, but the organic matter, growth of the crop, and time foster a new soil structure, perhaps even more porous than the soil was previously. This can happen in one growing season. In the case of compacted soils around trees, it can take years for a mulch laid over a compacted soil to correct the compaction.

Another way of looking at this is: if you can get the sampler into the soil, its likely not compacted, but if you have to use a hammer to get it into the soil it might be compacted (or dry). Pressure required is going to depend on the soil moisture, as well as the state of compaction. Compaction can also be measured by a device called a penetrometer which quantifies resistance to penetration. We as gardeners can use a screwdriver, if you can push it into soil; it is less compacted than if you can’t. The screwdriver test is also used to test for moisture content–when soils dry out, they resist penetration. The depth of water penetration in an irrigated soil is the depth to where the screwdriver stops when pushed in. So, it is easy to confuse a compacted soil with a dry soil. Also, if a soil is compacted, water will not easily enter, so many compacted soils are also perennially dry soils since irrigation does not easily penetrate them. This can be seen as increased runoff when you try to irrigate or ponding if the compacted zone does not drain away.

How do we fix compacted soils with high bulk densities? I was always taught that chemical fixers like gypsum, soil penetrants, or other chemical means will not affect a structurally damaged and compacted soil. The only way to fix them is to physically un-compact them. So, further destroying structure by ripping, drilling, trenching, air spading, or in some other way breaking up the compacted layers is the thing to do. Basuk (1994) cites cases where soil modified to treat compaction actually re-compacts (bulk density increases) over time (2-3 years after a compaction relieving treatment is applied). Numerous studies indicate that breakdown of arborist chip mulches will lead to reduced bulk density, but little is known about actual bulk density reductions with mulch applications over time. I am confident mulches will reduce bulk density, but given the diversity of soils, textures and compaction levels, I can only imagine this is a variable response. Removing the cause of the compaction, (foot traffic, machine usage etc) is the first step. Mulching following some kind of “soil fluffing” procedure should begin the process of increasing soil porosity and reducing bulk density. It may take years to relieve compaction passively through the action of mulching. If soil can be mechanically broken up, the compaction issue is solved and soil structure will slowly be reformed in time depending on what is grown thereafter.

References:
Bassuk, N. 1994. A review of the effects of soil compaction and amelioration treatments on landscape trees. Journal of Arboriculture 20:9-17.

Professional Credentials and Gardening Expertise: Entomologists

This is an installment of our series on professional credentials and gardening expertise. To read the introduction to this series, see Professional Credentials and Gardening Expertise.

Entomologists, Professional Credentials, and Designating Body

Entomology is the study of insects, and is a field within zoology, the study of animals. In the US, the primary professional and scientific society of entomologists is the Ecological Society of America (ESA), which formed in 1889 (ESA, 2019a). The ESA developed the Board Certified Entomologist (BCE) professional certification for professional entomologists with a bachelor’s degree or higher in entomology or a closely related discipline (ESA Certification Corporation, 2019a). The ESA later created the Associate Professional Entomologists (ACE) for those who don’t meet the education requirements of the BCE credential, but do have professional experience and training and work in the pest management industry (ESA Certification Corporation, 2019b). Both credentials are administered by the ESA Certification Corporation (ESA Certification Corporation, 2019a).

Relevance for Gardeners

An entomologist in white overalls sprays chemicals on a tree in a yard.
An entomologist sprays a tree to kill bagworms. Photo courtesy of the US Air Force.

Gardeners are likely to encounter entomologists in a few different capacities. First, professional certification of an entomologist is a sign of authority. This can be especially important when evaluating the credibility of information available online and reviewing the qualifications of authors. Gardeners should seek information from BCEs or ACEs, in addition to traditional sources of information on insect control like extension publications or peer-reviewed literature. Gardeners are also likely to encounter an ACE in the event that a professional is needed for helping with pest control – whether that be in the garden or in the home. If gardeners are seeking an insect control professional, an ACE professional credential is a good indicator of professional experience and training.

 

Type of Credential: professional certificate

The BCE and ACE credentials are professional certificates, which means that it is a voluntary program (Knapp and Knapp, 2002). Being a voluntary program, it is legal for entomologists to practice without the certificate. However, it will be up to gardeners to evaluate the experience, training, and education of the entomologist.

 

Education and Professional Experience Requirements

A bachelor’s degree or higher in entomology or closely related discipline (ecology, zoology, biology, etc.) is required for the BCE credential, while the ACE credential does require a college degree (ESA Certification Corporation, 2019c). BCEs are required to have three years of professional experience if their highest degree is a BS, two years of experience with an MS, and one year of experience with a PhD. ACEs must have 5 years of verified professional experience in pest management. In addition, ACEs must also have an active license or certificate that allows them to apply pesticides without supervision.

Qualifying exams

BCE certified entomologist must past the BCE Qualifying exam with a score of 70% or higher (ESA Certification Corporation, 2019d), while ACEs must pass the ACE exam with a 75% or higher (ESA Certification Corporation, 2019e).

Code of Ethics

BCEs and ACEs are bound by codes of ethics for the respective programs (ESA Certification Corporation, 2019f; g).

Continuing Education

BCEs are required to complete 120 hours of continuing education units via continuing education or professional participation over a three-year reporting period (ESA, 2019b). At least 72 hours of those CEUs must be from continuing education for each reporting period. ACEs are required to complete 18 CEUs over a three-year reporting cycle (ESA Certification Corporation, 2019f).

References

ESA. 2019a. About ESA. Entomological Society of America. https://www.entsoc.org/about/esa (accessed 27 August 2019).

ESA. 2019b. CEU Requirements. ESA Certification Corporation. https://www.entocert.org/ceu-requirements (accessed 27 August 2019).

ESA Certification Corporation. 2019a. About. ESA Certification Corporationf. https://www.entocert.org/about (accessed 27 August 2019).

ESA Certification Corporation. 2019b. ACE Certification. ESA Certification Corporation. https://www.entocert.org/ace-certification (accessed 27 August 2019).

ESA Certification Corporation. 2019c. BCE Requirements. ESA Certification Corporation. https://www.entocert.org/bce-requirements (accessed 27 August 2019).

ESA Certification Corporation. 2019d. BCE Examinations. ESA Certification Corporation. https://www.entocert.org/bce-examinations (accessed 27 August 2019).

ESA Certification Corporation. 2019e. Studying for the ACE Exams. ESA Certification Corporation. https://www.entocert.org/studying-ace-exams (accessed 27 August 2019).

ESA Certification Corporation. 2019f. Maintain my ACE Certification. ESA Certification Corporation. https://www.entocert.org/maintain-my-ace-certification (accessed 27 August 2019).

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.

 

Testing, testing, 1-2-3: Trialing new plants for the home garden

How do you know that plants will do well in your garden?  Do you research the types of plants for your region, study different cultivars, and select only things that have been proven to do well for your conditions?  Or do you buy what catches your eye at the garden center, plant it, and then see what happens?  I used to joke that my home garden was a horticulture experiment station, since I’d try all kinds of random plants or techniques and see what works for me.  Now, I get to do that as a fun part of my job through the All-America Selections (AAS) program. You’ve likely seen the AAS symbol on plants or seed packets at the garden center or in catalogs.  Heck, you may even have them in your garden (and not know it).  I compare it to the “Good Housekeeping Seal of Approval” that you used to see on appliances, cleaners, etc. The AAS program is a non-profit started in the 1930’s with the goal of evaluating new plants so that home gardeners can purchase high quality seeds and plants and to assist the horticulture industry in marketing innovations from their breeding programs.  You can read more about AAS and its history here.

A few weeks ago I traveled to Chicago for the All-America Selections (AAS) Annual Summit to receive their Judge Ambassador Award.  I had signed up a few years ago to be a trial site for edible crops for AAS.  The following year I talked my colleague Scott into signing up as a judge for their ornamental trials.  The fun thing about the program is that we get to grow all kinds of vegetables, fruits, and flowers that aren’t even on the market yet.  We get to see how well they grow compared to similar plants and rate them on a number of factors including growth habit, disease resistance, and performance plus flavor (for edible crops) or flower color/form (for ornamentals).  It can be hard work, but it is rewarding to help identify true plant innovations and to see your favorites be announced as winners.

How the testing works
While the AAS Trials may not have the rigor of academic crop research, I do appreciate the procedures in place that provide objective and high standard results.

Breeders, developers, and horticultural companies submit their new plants that are planned for future introduction to the board of AAS for consideration in the trialing program.  During the application process, novel traits of the plants are identified to ensure that the plant offers something new and exciting – these are the traits that judges will observe and score.  The board reviews the application to determine if it fits within the program rules.

Planting the vegetable/fruit trials.

One great thing about the program is that trial judges are professional horticulturalists from universities, seed companies, botanical gardens, etc. – they’re people who know how to grow things and know what quality plants look and act like.  There are trial sites all around the country, providing for replication and generalizeable results for most regions of the country. The conditions plants are grown in also vary by location.  My trial is at a farm where management is minimal.  When we were at the summit we visited the trial gardens at Ball Horticulture which looked much more maintained and pampered compared to mine.  This gives data on a variety of maintenance levels as you’ll find in home gardens – some gardeners are very conscientious about maintaining their plants and others have a more laissez faire approach.  In order to win as a full national AAS winner, the plants have to perform well across the country in all these different situations.  Sometimes those that perform well in a few regions but not the others will be designated as regional winners.

Second, the tests are blind.  This means that we do not know what the exact plant is, who the breeder or seed company is, or any other info other than what type of plant it is.  To the judge, each entry is just a number.  It could be from a seed company you love (or hate), your best friend, the breeder who was your advisor from grad school, etc.  This makes the results fair and reduces the chance for bias toward or against a plant based on its origins.  The ratings are just based on the plant.

Another part of the trial is comparison.  It is one thing to grow a tomato plant and say “yep, that’s a good tomato.”  Its another to grow a tomato and compare it to similar cultivars to say “yep, that’s a good tomato….but it is better than what’s already available on the market.”  The goal of the program is to show how new plants have merit over older plants.  We only need so many new tomatoes (and let’s face it, there are lots of new tomatoes – we test WAY too many in the AAS process for my liking).  The board of AAS judges reads the entry info from the new cultivar being tested and selects plants (usually two) to compare it against.  If the trial is a yellow cherry tomato, it will be grown and tested alongside other yellow cherry tomatoes.  The scoring is based on whether its performance or taste is as good as or better than the comparisons.  If most judges don’t rank it as “better” then it has no chance of winning.

Confidentiality and Proprietary Plants

The fact that the testing is blind, paired with the fact that results of “failed” tests are not released, lends itself to confidentiality.  Another important factor about the testing is the proprietary nature of the tests and test sites.  These are new plants that haven’t been introduced to the market (except for the case of perennial trials) and are usually for proprietary or patented plants.  Test sites should have some sort of control over who enters them and signs prohibiting the collection of seeds, pollen, or cuttings are placed at the site.  Believe it or not, the world of plant introductions can be dog-eat-dog and cutthroat.

So what if it doesn’t win?

One of the cool things about the test is seeing the announcements of the winners early the following year.  You see the list of plants and think back to what you grew the previous season.  If often find myself thinking “oh yeah, I remember that plant, it did really well” and sometimes even “how did that win, it did horrible for me.”  This is a good reminder that we can’t base generalized garden recommendations on anecdotal evidence.  What did well for me may not work for someone else and vice versa.  All the results from the test sites go together to provide a general view of the plant performance.  It will do well for some and not others.

So if most of the judges rank the crop as not performing, looking, or tasting as good as the comparisons the plant doesn’t win.  And that’s it.  Due to the confidential nature of the testing you won’t know that it failed the test.  Even I won’t know that it failed the test. It will likely go on to market without the AAS seal where it will face an even tougher test – the test of consumer demand.  Of course, many people may grow it and be successful, and some may grow it without success.

What are the AAS Winners and how do I find them?

There’s a list of plants announced each year through the AAS website and social media channels.  You can find a list, in reverse order of winning (meaning most recent first) on the AAS Website.  The site also has a searchable database if you’re looking for a specific plant.  Since these plants are owned by lots of different seed companies and breeders, there’s also a retailer listing on the site.  The AAS program also supports a number of Display Gardens across the country, including botanical gardens, university gardens, and others where the public can see the most recent winners growing.  Here in Omaha we maintain a display garden for the ornamental plants at our county fairgrounds.  We also have our on-campus garden which is used for our TV show Backyard Farmer (the longest running educational TV program in the country, BTW) which serves as a display garden for both ornamental and edible crops.

I recently shared the AAS Testing Program with the local news here in Omaha. Check it out:

 

Some of my favorite recent AAS Winners
Pak Choi Asian Delight AAS WinnerAsian Delight Pak Choi – this was planted in May and didn’t bolt.  We were still harvesting it in October.

 

 

 

Pepper Just Sweet - 2019 AAS Edible-Vegetable Winner

Pepper Just Sweet – these plants were big and healthy even when everything else was struggling.  The peppers were delicious.

 

 

 

Potato Clancy - 2019 AAS Edible-Vegetable Winner - The first potato grown from seed!

Potato Clancy – potatoes….from seed!  Just fun!

 

 

 

 

Pepper habanero Roulette - 2018 AAS Edible - Vegetable WinnerPepper Habanero Roulette – All of the fruity sweet, none of the heat.  A fun heatless habanero.

 

 

 

Dianthus Interspecific Supra Pink F1 - 2017 AAS National Winner - This compact, bushy plant blooms prolifically with novel mottled pink flowers sporting frilly petal edges that hold up even in summer heat and drought.Dianthus Intraspecific Supra Pink– A reblooming, prolific Dianthus with interesting ruffled flowers.

 

 

 

Eggplant Patio Baby – container sized eggplant with mini fruits perfect for cooking or roasting whole.

 

 

 

Ornamental Pepper Black Pearl 2006 - AAS Flower Winner - Black Pearl is a handsome plant with black foliage.Ornamental Pepper Black Pearl – Cute purple flowers lead to these shiny pepper pearls.  Love the black leaves, too.

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).

Is there a “Deathstar” in your garden?

If you follow national news, you may have noticed that Sudden Oak Death disease caused by Phytophthora ramorum has been found again in a new state and has escaped into retail commerce and thus into gardens. This is news because the disease is a killer of rhododendron, oak, camellia and many other ornamental plants. Yesterday I was measuring trees in a research plot here in California and I found that one of my subjects had turned brown and lost all its leaves. On checking, I discovered a Phytophthora collar rot was the cause of the symptoms. Phytophthora diseases kill woody plants, often our cherished specimen plantings. This blog post is to introduce you to Phytophthora collar rots, their diagnosis and treatment.

A Phyotophthora crown rot canker on ghost gum
This Eucalyptus suddenly collapsed from a Phytophthora basal canker. All the leaves remain on the tree and turned brown
Planting too deep is predisposing to Phytophthora infection. Note the aeration tubes could not save this tree–they serve no function in landscapes. Avoiding over-wet conditions, proper planting and irrigation timing would have prevented this Phytophthora death.

Phytophthora means plant destroyer in Latin. It is the “deathstar” of plant destroyers and once it has infected, death is the usual outcome. All Phytophthoras are Oomycetes. These are organisms that form an Oospore. Oospores are usually produced when two strains of Phytophthora join and the sexual organs form resulting in this spore. It is thick walled and can live for years in soil without a host. Phytophthora used to be considered a fungus but this was changed some years back to put all Oomycetes in groups that are more closely allied with brown algae. Phytophthoras are not in the kingdom fungi but rather the SAR supergroup of organisms. One main difference between these microbes and fungi is that Phytophthora has cellulose in its cell walls just as plants do. There are hundreds of species of Phytophthora, most affect flowering plants especially woody plants. Very few affect grasses and monocots. There are some that affect palms and others, vegetables and herbacious plants. The late blight fungus Phytophthora infestans caused the Irish Potato famine that resulted in millions of deaths (of people and potatoes) and migration (of people not potatoes) to the United States to avoid starving further.  caused the famous Jarrah (a Eucalyptus spp.) die off in Australia, one of the largest known forest epiphytotics. Phytophthora species occur worldwide and affect plants in almost every garden.

Why are Phytophthoras so successful and how do they get into gardens? I think the answer is that they are cryptic. You can not see any of the spore stages, even with a microscope. There is no “mold-like” growth of the pathogen that you can see either in soils or on the plant. This is because the organism lives inside plant tissues and is very reduced in soils where is survives as spores. Unlike many fungi, you can’t see the mycelium of most Phytophthora species. In plants, Phytophthora usually grows in the vascular cambium of roots or stems and kills those tissues. Plants react to Phytophthora by producing phenols and other phytochemicals turning tissues brown. Brown roots or spreading brown cankers on the main stem are common. When Phytophthora kills the tissues on the main stem this often causes a basal stem canker near the soil line. Usually the plant collapses rapidly with all the leaves turning brown or falling from the plant suddenly. Sometimes basal cankers are associated with deeply planted trees and shrubs or where soil has been added over the root collar. Since basal cankers are under the bark they may not be visible while active and need to be revealed with a knife to expose the brown tissue.

Phytophthora diseases are increased by excess water in soil or on plants. Overly wet situations are predisposing to these diseases if the pathogen is present. Other conditions like reduced oxygen in the rootzone (from compaction), increased salts in soil, very dry conditions followed by very wet circumstances all promote Phytophthora. There are also some groups of plants that seem to be very susceptible—these include: rhododendron, camelia, oaks, cyclamen, most plants in the Ericaceae (madrone, manzanita, blueberry etc.), cedars, pines, and the list goes on. It is hard to avoid susceptible plants because there are so many of them.

Phytophthora species are not native everywhere but have been distributed far and wide by people. Nurseries are prime disseminators of Phytophthora infested plants. Fungicides “subdue” the pathogen but do not eradicate it. So a plant can look healthy while still being infested with Phytophthora. When the fungicide wears off, the plant may become sick if conditions are right for the Phytophthora to grow. Another reason why this type of pathogen is so successful is that a plant can have 50-75% of its roots killed before symptoms begin to show on above ground plant parts. Wilt and collapse only occur very late in the progress of the disease. Because of this, it is important to inspect plants before bringing them home. Never purchase a plant with brown feeder roots, or this could be the starting point for Phytophthora in your garden.

If you are an avid gardener who likes to try new plants all the time, then your future encounter with Phytophthora is likely inevitable. You can do things to limit its development.

Mycelium of Phytophthora exposed to cellulase (left) and healthy mycelium (right)

-Plant on berms or mounds while avoiding planting in low or poorly drained places
-Use wood chip mulches from freshly chopped tree parts
-Add gypsum to soils as part of your mulching protocol
-If you irrigate your garden allow drying out periods between irrigations
-Plant “high” so that the root crown is clearly exposed
-Do not volcano mulch or cover the root crown with anything at all
-Avoid planting woody perennials in turfgrasses or lawns

Fresh wood chips are often broken down by fungi that release cellulase, this enzyme is toxic to all Phytophthora’s, and the reason why FRESH mulches are so important to create soils with cellulytic enzymes that destroy this pathogen. As gypsum dissolves it provides a slow release source of calcium ions which are also toxic to the swimming spores of Phytophthora. While fungicides can also help limit Phytophthora development, the cultural practices listed above will be just as important in preventing and limiting root and crown rot disease in your garden.

Give me your huddled root masses yearning to breathe free

About this time last year I posted photos of the installation of my new pollinator gardens (all perennials). As you can tell from the photos below, all of these plants have not only survived but thrived with their midsummer rootwashing.

Garden 1. Robust perennials! Except for the the sad, tiny lavender in the lower right hand corner (discussed below).
Garden 2 is just like the other, except the strawberry groundcover is replacing the wood chips.

 

 

 

 

 

The only ones that didn’t make it were the six Lavandula stoechas ‘Bandera Purple’ (see above). They did fine through the summer and well into winter. But with our surprise snowstorm in February (along with a 20-degree temperature drop in one night – from 33 to 14F), all but one of these marginally hardy plants (USDA zones 7-10) gave up the ghost. I won’t make that mistake again. But I will continue to root wash ALL of my perennials before I plant.

It’s pretty easy to excavate this tree (planted months ago) since there is NO root establishment.

And since it’s Independence Day here in the US, I thought I’d continue with the “free your roots” theme and discuss the medieval torture system that passes for recommended B&B tree installation practices. I’m talking about the burlap, the twine, and the wire baskets that are left on the root ball and cunningly hidden underground to do their damage over the years.

THIS is what should be planted.
Not this.

 

 

 

 

 

There is a great deal of disagreement about what to do with all the foreign material that’s used to keep tree root balls intact during shipment. To be clear, that is the ONLY thing they are intended to do. There is no research that shows leaving them on benefits the tree at all. The reason they are left on is because it’s more economically feasible for the installation company to do it this way. Personally I think that’s a pretty crappy reason, particularly when you are looking at trees that can cost hundreds or thousands of dollars.

Does anyone seriously think this is a good way to plant trees?

Most studies that have addressed the issue have been short term: two or three years, rarely longer. Irreversible damage to roots can take years to develop. It’s useful, therefore, to look at the landscape evidence to see what happens with all these barriers to root growth and establishment.

Death row.

Arborist and landscape designer Lyle Collins recently excavated the remains of trees that had been installed in 1991. The trees had died years ago and certainly hadn’t grown much as evidenced by their trunk size.

Not much trunk growth in this tree.

But while the trees didn’t survive, the burlap, wire basket, and webbing were all still there almost 30 years later.

Basket and webbing are clearly visible (after washing)…
…as is the burlap (before washing)

 

 

 

 

 

 

 

The clay rootballs are nearly intact as well. That’s not what you want to see. Roots must establish outside the rootball into the native soil, or they won’t survive.

Intact rootball after 28 years
The same rootball after washing

 

 

 

 

 

 

 

Eventually I’m convinced long-term research will show the folly of leaving foreign materials on the rootballs of B&B trees. In the meantime, I’ll continue to plant trees in a way that ensures their roots are in contact with the native soil and free from any unnatural barriers to growth.

 

 

 

Urban Gardening Considerations

Along with the trends of buying local food, buying organic, etc., there seems to be an increasing interest in the ultimate local food source – a garden. This includes in urban areas. Urban gardening is a great way to save money on food, a great source for fresh vegetables – especially in “food deserts”, and an easy way to introduce kids to where the food on their plate comes from. However, there are a couple potential obstacles you should consider first before starting your urban garden.

"Graze the Roof" by Sergio Ruiz
“Graze the Roof” by Sergio Ruiz

First, in urban environments the possibility that soil could have been contaminated with heavy metals, petrochemicals, etc. is pretty high, especially in older neighborhoods. Lead, which was once a common additive to gasoline and paint, is a common contaminant in urban soils.  and can be absorbed by the roots of the vegetables you grow. Because of this, that lead can eventually end up in the food on your plate. Most lead poisoning comes from ingesting lead (like eating lead paint chips…), so it’s important to know that the soil you’re using for your garden is safe. You should take some soil samples and send them to a lab in your state that can test for heavy metals like lead. Usually the Land Grant university in your state (if you’re in the US) will have a soil testing lab where these tests can be performed for a nominal cost. Other forms of contamination are possible as well, such as chemicals from cars, asphalt , laundry-mats, etc. These chemicals are more difficult to test for, so your best bet is to find out the history of your garden plot. These records should be available from your local city government, perhaps even online. Read more about contamination in this post.

Second, urban soils are often compacted from foot, car, or perhaps machinery traffic. Compacted soils make it difficult for plants to grow, mainly because the plant roots are not strong enough to penetrate the compacted soil, and thus cannot gather enough water or nutrients for the plant to survive, let alone grow and produce vegetables. Compacted soils are especially common in newer housing developments where entire blocks of houses were built around the same time. The construction companies often remove all of the topsoil prior to building the houses. The soils are then driven over by construction machinery and compacted. Then sod is laid directly on top of the subsoil. This makes for soils with very poor growing conditions for both lawns and gardens.

A good alternative for areas with either contaminated or compacted soils is to use a raised garden bed with soil that was brought in from a reliable source. You can buy bags of potting soil from a local home and garden supply store, but a more economic alternative is to have a trailer full of topsoil trucked to your raised bed. When you build your raised garden, be sure to use untreated wood. Some of the chemicals used to for pressure treated lumber are designed to kill fungi that break down wood. These chemicals, some of which contain arsenic, can leach out of the wood and into the soil used for your veggies! However, untreated wood, though it might not last as long, will still last for decades and is probably cheaper anyway. There are lots of great designs and how-to sites that show you how to build a raised garden bed. Here’s an extension bulletin from Washington State University on raised bed gardening. The raised beds shown below are from when I first installed them in my community garden plot in Manhattan, Kansas. One is now a strawberry patch (the border helps contain the strawberries to a defined area), and the other is used for mostly cold season crops.

This image shows two raised garden beds with freshly added soil and surrounded by straw in a garden plot.
Raised garden beds in Colby Moorberg’s community garden plot.

Space is also another consideration. If you don’t have the space for a garden or a raised garden, then perhaps you need to think outside the box (raised garden pun intended) and consider container gardening. Container gardening is exactly what its called – growing ornamental or vegetable plants in containers. Containers can be traditional plant pots, buckets, plastic totes, or any other container with an open top.

The advantages of container gardening include:

  • Containers can be arranged to optimally use the space available, or rearranged if you like to mix things up sometimes
  • Potting soil can be used, and can be trusted to be lead/chemical-free
  • Work can be performed on a bench, thus avoiding working on your knees
  • Containers can be arranged to provide decoration for your outdoor space
  • Many objects found around the house can be cheaply converted into decent containers
Vertical Pallet Garden. Photo by Heather Foust

Vertical gardening is a version of container gardening that uses your available space  efficiently. Much like using shelves to save space inside your home, vertical gardens use shelves, stairs, racks, etc. to make use of vertical space. The options for vertical gardens are only limited by your imagination. Here are a few extension bulletins on vertical gardening from Tennessee State University and the University of Nebraska.

The main disadvantage of container gardening is that you’ll likely have to water more frequently, but there are strategies to overcome that problem – see my prior blog post about saving water with container gardening. Another good resource is the University of Illinois Container Successful Container Gardening website.

In summary, the biggest obstacles to urban gardening are soil contamination, soil compaction, and space limitations. I’ve given you a few good alternatives to overcome those issues. Also, be sure to fertilize appropriately, lime as needed, and make sure the plants that you pick are appropriate for the sunlight that’s available. Your local garden supply store or extension agent can help you with suggestions on those issues.

If you know of an urban gardening obstacle that I didn’t address, please leave a comment and I’ll see if I can help out.

Happy digging!

Colby

This was originally posted on Colby’s soil science blog, ColbyDigsSoil.com. Some edits, updates, and adaptions were made for this post.

The Dog Days are here

The dog days of summer are here and as we approach the longest day of the year (summer solstice is June 21st), we are also feeling the advance of high summer temperatures. Long days mean more evapotranspiration and water withdrawal from the soil. During these long days, plants photosynthesize more, grow more, and use the most water during the month of June.  In fact evapotranspiration looks generally looks like a bell shaped curve when plotted by month (figure 1).  Soils dry quickly and irrigation or rainfall may not keep

Figure 1. Evapotranspiration data by month. Image from US geological Survey

up with plant demands for water. This can bring some very real stress to garden plants and turfgrasses.  If you live in a place that does not receive summer rainfall you will certainly need to increase irrigation to reflect day length at this time of year.

Transpiration is water loss through leaves and is not  part of photosynthesis, but it is critical to cool the plant. As soils dry out, the level of abscisic acid produced in roots increases and translocates to leaves resulting in the closing of the pores called stomates. Closed stomata reduces transpiration, but only at a steep cost to the plant. That cost is heat build up. Since this is also the time of the hottest weather it is not long before leaf temperatures rise to lethal levels and sunburn results. Sunburn is always seen as damage in the middle of the leaf because that is the hardest spot to dissipate the heat. The edges that lose heat rapidly are usu

Figure 2. Sunburn occurs in the middle of leaves as in this Windmill palm (Trachycarpus fortunei)

ally not burnt (Figure 2).

Short of applying water properly, what else can be done?   Mulches are a great way to avert drought stress since they reduce water loss from the soil surface. The effect is greatest where sun hits the soil. So in new gardens or gardens without a lot of shade, mulches are essential during hot weather to reduce plant stress. Wood chip mulches are particularly helpful in that wood does not reflect, hold or emit heat as much as soil, so it protects adjacent plant surfaces from heat.

How about water absorbing polymers or hydrogels? While much of the allure of these “water crystals” has worn off, it is still good to remind that polymers don’t change evapotranspiration rates of plants so even if they did all the things they claim to, they won’t get plants through a hot summer any better than if they were not present in the soil.

With the longest days come warming soil temperatures.  Hot soil can affect plants especially perennials.  Ground that is not mulched will radiate infrared onto plant surfaces, this can increase stress. This is yet another reason to employ wood chip mulches around perennials.

Figure 3. Impact sprinklers raise humidity on very hot days relieving plant stress

So when it is particularly hot and dry how can we get plants through this stressful time? Running sprinklers (where practical) will increase humidity and if soils are dry reduce stress (Figure 3).  For annual plants, some shade is often helpful. Applying shade cloth to sensitive or newly planted/emerged plants can cut stress dramatically.  As plants establish, the shade can be gradually removed.  Keep irrigation even so moisture is always there to maintain transpiration — this  is essential during warm weather and long days. For perennial plants there is not much to be done. While pruning will reduce the amount of surfaces that lose water, pruning (thinning) will also lead to temperature increases in the plant canopy since the evaporative surface area of the plant is decreased. So while soil water is saved, canopy temperatures may rise, this may be a poor trade off in the hottest months of the year.  Over-pruning opens plants up for sunburn on stems which can lead to fungal canker infections by pathogens like Botryosphaeria. This is very common in Apples.

Another treatment you may have heard claims for are anti-transpirants. These are products that are sprayed on plants to create a film that will cut water loss from leaves. Taken from a recent Amazon search I found the following product description recently… “Product is a water-based, semi-permeable polymer coating that can minimize the damages from climate related stresses, such as frost and freeze, heat stress and sunburn, drying winds, and transplant shock. Applied as a foliar spray, Product provides a unique non-toxic, biodegradable, elastic membrane over the plant surface to reduce moisture loss and insulate the plant.” While there may be an application (such as freeze protection) that makes sense for this kind of product somewhere, I don’t see it in your garden during hot weather. Cutting transpiration (“reducing moisture loss”) will increase the heat on leaves, so one of the common side effects of using these products is hot weather is damage or phytotoxicity.  Like polymers the fad is faded.

Sometimes the dog days of summer bring insurmountable challenges. In early summer of 2018 in California, temperatures reached record levels of 115-120. Even in irrigated situations plants were damaged, short of providing immediate shade, there was nothing to be done and many plants were injured, even native plants are not adapted to such high temperatures. If these conditions occur in your garden, you may not be able to limit damage, but there are considerations for after care when this kind of blitz occurs. Don’t prune anything immediately, let the leaves fall and buds form because stems may be intact. Prune away injured plant parts after regrowth begins. If injury is severe, cut back on irrigation. Injured plants don’t require as much water because there is less functional  leaf area. This is why root root rot often follows this sort of severe injury. The summer solstice is here—I can already feel the shortening days of fall some distance away.

Reference

Costello, L.R., E.J. Perry, N. P. Matheny, M.J. Henry, and P.M. Geisel.  2014.  Abiotic disorders of Landscape Plants.  University of California Division of Agriculture and Natural Resources Publication #3420.

Cornmeal magic – the myth that will not die

Way back in 2010 (and then again in 2012) I wrote about a bizarre belief that cornmeal could be used to treat fungal diseases, from lawn spot to athlete’s foot. Rather than rehash what’s already been written, I’ll invite readers to read those posts for background. And of course look at the comments, which are…interesting.The weird thing is that this post from 2010 is the single most popular post on the blog. (Our stats are only for the last two years since we migrated the web site – who knows how many there were before May 2017?)

Blog stats over two years

The consistent popularity for the topic spurred me to publish a university fact sheet on the use of cornmeal and corn gluten meal in home landscapes and gardens. This fact sheet reviews the pertinent literature, and makes recommendations that are pretty much the same as those I made almost 10 years ago. Nothing has changed in the research world to support cornmeal as a fungicide.

But wait, there IS something that’s happened since 2010! Now cornmeal is being touted as an insecticide! In fact, if you go to Google and search for “cornmeal” and “insecticide” you’ll find thousands of hits.  As you might expect, there’s no research to support this notion: researchers in Maine, for instance, found no effect of cornmeal on fire ants. However, it is used as a bait to deliver actual insecticidal chemicals.

Way back in 1937.

But facts don’t get in the way of home remedies, such as Lifehacker’s eyebrow-raising advice.

Hmmm…

By refining the search to only include university websites (use “site:.edu” to do this), and swapping out “ants” for “insecticide,” you’ll find at least one Master Gardener group happily (and illegally) recommending cornmeal as an ant killer. The popular mode of action is either (1) they can’t digest cornmeal and starve or (2) the cornmeal absorbs water in their gut and they explode.

Boom!

This reminds me of yet another food product – molasses – recommended for killing ants. Since you’re already here, you might as well check out Molasses Malarkey parts 1, 2, and 3 too.

Might I recommend everyone use their cornmeal and molasses to make bread or cookies or pancakes? There are some delicious recipes on the internet.

Yum!

Bare Rooting – a guest post from a commercial landscaper

What are these trees and do they look like this? Read on to find out!

Today’s blog post is courtesy of Mary Blockberger of Sechelt, BC. As you’ll see, Mary and I go way back.  I thought it was important to our ongoing discussion to see how the industry can use the root-washing technique effectively and economically. Here’s Mary:

“Before I began managing the Sunshine Coast Botanical Garden in Sechelt, BC I had a small residential landscaping company.  By small, I mean that I was the employee of the month every month of the year!  One of our Garden’s mandates is to provide relevant and educational programs for our community.  Dr. Linda Chalker-Scott has been one of our most popular speakers several times.  One of her presentations dealt with the practise of bare-rooting perennials, shrubs, and trees prior to planting, and the tremendous advantages of following this method.

Root-washing and installing 36 Carpinus. November 2007.

“In November, 2007 I had a chance to try this technique out.  My client wanted a ribbon of Carpinus betulus ‘Fastigiata’ planted that would eventually be pleached into an interesting pattern.  [Pleaching is a formal tree training technique.] There was a total of 36 trees to be planted; most were container stock as I recall but there may have included a couple of B&Bs as well.  Working with another local landscaper, into a wheelbarrow of water went every single tree one at a time.  The dirt was clawed away from the root balls by hand with a final spray from the hose.  Honestly, it was a cold and miserable job, and I believe a few curses directed at Linda ensued.  However, once the roots were cleaned of all soil planting was a breeze.  It’s a lot easier moving trees without moving the soil too.

Carpinus are well established and pleaching is underway. April 2009

“Flash forward 12 years, and every single tree has flourished.  Bare rooting allowed us to identify and correct any problems before planting, and I’m sure this has a lot to do with the trees’ success.  It’s a time consuming and at times messy method, but the reward of a healthy row of trees is well worth the effort, IMHO.”

Pleached Carpinus hedge May 2019

And let me add to Mary’s account that a ZERO replacement rate is going to pencil out to long term economic success. I was able to see these trees earlier this year – that’s my photo at the top of this post.