It seems so simple to plant a tree. But to grow a tree is more difficult! In many parts of the United States there is enough water for trees and turfgrass, but it is often a bad idea to mix the two. You may have observed that sometimes young trees do not grow as well when planted in turfgrass. Certainly this is a generalized view and tree/turfgrass genetics are very different between their respective species. So it is natural to expect different outcomes when planting different species of trees in any landscape setting, turfgrass notwithstanding. Another factor to consider is time. The day we plant a tree is not the same time reference as ten years later. In ten years, the tree if it is successful, may have modified
its environment significantly, making turfgrass cultivation more difficult. Most tree/turfgrass difficulties begin when the tree is young–as a newly planted tree. If it succeeds in growing a large canopy, difficulties will ensue for the turfgrass. Sometimes turfgrass cultural requirements (frequent irrigation) can predispose trees to root or root-collar diseases such as Phytophthora.
Trees and turfgrass have some similar and very different requirements from their respective landscape settings. Both trees and turfgrass require sunlight to photosynthesize and grow. Both would usually prefer full sunlight without shade. As trees grow they shade the turfgrass sward beneath their canopies. Turfgrass can lose density, and become a thinner sward that is more susceptible to diseases such as powdery mildew. Trees grow roots near the soil surface and as they become larger, some trees may even proliferate roots near the mowing height of turgrass and suffer repeated injury from mowers, also increasing the risk of pest invasion into the tree. Both trees and turfgrass need water and soil minerals to grow. While soil minerals are usually abundant enough for both, water is often limiting for one or the other in this landscape combination.
The maintenance practices required for turfgrass often injure trees, especially young trees. Mowing near trees can injure the bark on the lower stem especially if the mower comes to close and actually scrapes the young stem. Since grass will grow longer where the mower can’t reach right near a tree stem there is a temptation to use a string line trimmer or weed whip to maintain the grass that has shot up around the tree stem. The repeated use of string line trimmers around trees removed young bark and can “girdle” the tree stem. While trees can survive these practices their growth rates are slowed considerably.
One approach to having trees growing with turfgrass is to remove a ring of turf away from the tree and replace it with mulch. This eliminates the need to maintain the turfgrass near the trees stem and root flare. Richard Harris and others (1977) found many years ago that a one foot circle removed around the stem of newly planted trees would increase their establishment rates compared to trees with turfgrass growing right near the stem. Whitcomb (1979) also recognized that turgrasses are competitors with newly planted shade trees. Whitcomb’s earlier research (1973) showed reduction in root density when trees were planted in a sward of Kentucky bluegrass.
As trees grow it is important to widen the ring around them giving more room for mulch and reducing the competing turfgrass underneath their expanding canopies. This is a general concept; some trees can live in turfgrass without problems as long as resources are not limiting. Riparian trees such as sycamore can grow well in swards of turfgrass, but other species such as Peruvian pepper (Schinus mole) tend to languish.
Trees are adapted to drop leaves, this is termed litterfall and it becomes part of their natural mulch. Litterfall tends to prevent annual plants such as grasses from developing. Fallen leaves, fruit and twigs are recycled by fungi providing nutrients back to the tree. Turfgrass cultivation interrupts this process and while trees obtain some of the nutrients supplied to turfgrass, as Whitcomb observed, turfgrasses are fierce competitors for nutrients so young trees are especially susceptible to nutrient deprivation in turfgrass swards. For the best results in your
garden, it is best to maintain some distance between young trees and turfgrass. It is optimal if the mulched (no turf) area under a tree can expand to its dripline as it grows.
It seems that as interest in gardening grows, especially among younger generations, interest in different techniques that home gardeners use and different plants they grow are also on the increase. You see the old standbys like straw bales and containers emerge. Terraria, succulents, and air plants are having their moment. And all kinds of technology driven indoor growing systems are all over the web, mostly hydroponic, but some aeroponic and aquaponic as well (we’ll talk about the difference in a bit – if you’re just here for that, skip the first 2/3 of the article).
I had been thinking about getting one of those new techno aeroponic growing systems as a demo for my office as a discussion starter for those interested in controlled environment growing whether on the homework commercial scale. There is a general interest and need for basic education for hydroponics and aquaponics in the area that I hope to build extension programming around, so having something at the office could provide some interest from walk-in and social media clients. I had dusted off a first generation AeroGarden that I found in the storage shelves in the office storage catacombs and set it up in my office. It is a far cry from the new models I saw in those online ads that are outside of my budget for “toys to show off at the office.” It doesn’t have nice LED lights or connect to my phone via Bluetooth like the fancy new models. Given its age, it produces more noise and heat than the lettuce and herbs I’ve tried to grow in it. Maybe I’ll be able to get one of the fancy models one day.
Then I remembered a book that an urban ag friend of mine had written on building DIY hydroponic systems from common building materials and resolved to not only build a system, but incorporate it into my programming somehow. The book, appropriately titled “DIY Hydroponic Gardens: How to Design and Build an Inexpensive System for Growing Plants in Water” by Tyler Baras shares plans for building a variety of types of hydroponic systems using basic building materials like gutters and lumber, drip irrigation tubing and fittings, and various other bits and bobs. Tyler had been a featured speaker for the West Virginia Urban Agriculture Conference that I started and hosted when I worked for WVU Extension, so the book was on my radar – I placed an order. (Note: I don’t get a kickback for sharing the book – just sharing a good resource that happens to be from a friend.)
Teaching Hydroponics to an Unlikely Audience
As luck would have it, I had an opportunity to put the book, and my DIY hydroponic skills, to the test. Our university does quite a bit of work with and in Rwanda and in May I had the opportunity to travel to Rwanda as part of a study abroad program with my Ph.D. advisor. Rwanda is a very small country, just under the size of Massachussets, with a very big population by comparison – 12 million vs 7 million! Feeding that many people is a struggle, and even though Rwanda produces a lot of produce (and more lucrative export crops like coffee and tea), it still imports a lot of its fruits and vegetables. We were studying how innovation spreads in rural areas, and just before our trip I found a news article sharing that there would be an upcoming $8M USD ($8B RWF) investment in hydroponics in the country in order to increase production on the limited amount of land available.
In June I was scheduled to teach a group of Rwandan exchange students that are part of a sponsored program at the university, and remembering the planned investment in hydroponics I planned to add DIY hydroponics to the curriculum. This is fitting, since most small-scale operations would rely on finding what materials would be locally available. While the operations started by the investment would likely bring in “real” hydroponic systems, if small scale producers want to use the technology or if individuals want to build skills, they’re going to have to use what is at hand.
It was interesting teaching an audience who were interested in learning about the new technology, but have little experience or general knowledge on the subject. Even more interesting was the fact that many of the students had not used or even seen some of the basic power tools we used in building the system. I’m no shop teacher, but in the end the students not only learned a little bit about hydroponics and hydroponic systems, but also some skills using tools that they can apply in other applications.
Hydroponics, Aeroponics, & Aquaponics – Oh My!
Earlier I mentioned that there are differences between hydroponics, aeroponics, and aquaponics. In some ways, they use similar basic setups. All are based on soil-less growing using an inert media to support plants, supplying nutrients and water directly to the plant roots, and providing light to the plants using either natural sunlight or supplemental lighting. Differences come from the source of plant nutrients and from how they are delivered to the plant. I thought I’d take a few minutes to talk about the basics of each of the techniques so you can understand the differences just in case you want to buy or build your own system. If there’s interest, I hope to focus on hydroponics and controlled environment agriculture over my next few blog posts – tell me what you’re interested in learning.
Most people are familiar with the concept of hydroponics. This technique relies on roots being submerged in a nutrient-rich solution where the nutrient content is engineered from a variety of mineral sources. There are a variety of different systems (that will hopefully be the subject of an upcoming blog) where the root zone interacts directly with the solution. In some cases, roots are submerged in a large volume of solution while in others a film or shallow stream of water flows through the root zone. Systems where roots are submerged in the solution may simply be a large reservoir where the plants float on top where systems relying on flow may involve a pump. Movement of water adds another plant need -oxygen, which is required for respiration by the roots. In systems where there is no flow, air is often pumped in to provide oxygen.
Most flowing systems are recirculating, where the solution returns to a reservoir and is pumped back into a reservoir to be reused. While it may seem counterintuitive, these recirculating water based growing systems have been touted as production methods that conserve water. That’s why some of the leading hydroponic production and research comes from areas of the world where water is scarce. Less common are flow through systems where water and nutrients are not recaptured but discarded after initial use.
Aeroponic systems have much of the same basic setup but instead of the roots interfacing directly with water solution it is applied as a pressurized mist. These systems generally use a much smaller volume of water, but there are some drawbacks. Failure of the system, such as an electric outage or clogging of the nozzles that pressurize the mist (which is a common occurrence) can quickly result in plant failure since roots can dry out quickly. Several systems that are sold commercially that market themselves as aeroponic, such as the AeroGarden or Tower Gardens, are more similar to a flowing hydroponic system than a pressurized mist aeroponic system.
The plant growing structures of aquaponics are similar to those of hydroponics, with the addition of larger reservoirs to accommodate the addition of aquatic livestock such as fish (or sometimes crustaceans). The waste produced by the stock provide the nutrients needed by the plants rather than an engineered nutrient solution. These systems require having the technical knowledge to meet the needs of the aquatic stock and balancing those with the needs of the plants. The addition of the aquatic stock also introduces a microbiome of bacteria and fungi, many of which are required for animal health but can also introduce pathogens that can negatively affect human health.
Are you interested in learning more about these systems? What do you want learn about in hydroponic or other systems? Let me know in the comments and I’ll try to base some future articles on what our readers are interested in.
Arborists, Professional Credentials, and Designating Bodies
The Merriam-Webster dictionary defines arboriculture as “the cultivation of trees and shrubs especially for ornamental purposes” (2019a) and arborists as the specialists that care for those trees (2019b). In the US there are two primary certifications for arborists. Arborists can become a Registered Consulting Arborist (RCA) through the American Society of Consulting Arborists (ASCA) (ASCA, 2019a) and/or become an International Society of Arboriculture (ISA) Certified Arborist (ISA, 2019a). The ISA also offers a range of associated certifications, including ISA Certified Arborist Utility Specialist, Arborist Municipal Specialist, Tree Worker Climber Specialist, Tree Worker Aerial Lift Specialist, Board Certified Master Arborist, and ISA Tree Risk Assessment Qualification. For the sake brevity, the focus of this post will be on the flagship programs from each organization, ASCA’s Registered Consulting Arborist and the ISA Certified Arborist credentials.
Relevance for Gardeners
Many gardeners who have trees are likely familiar with arborists, or at least with a local “tree guy”. While trees are beautiful, they can also suffer from disease, nutrient deficiencies, and other plant health issues. In addition, trees often require maintenance and pruning to ensure safety, avoid damage to houses or other property from falling branches, or to allow more light through the tree canopy to reach the ground and garden. Maintenance and pruning of trees requires experience and expertise to ensure that trees aren’t damaged in the process, and that pruning is done safely. When their services are needed, hiring an arborist with professional credentials can be an excellent way to ensure that trees are properly cared for and that nobody is hurt in the process.
In my personal experience, certified arborists in my community charge more per hour. However, the extra cost in exchange for ensuring the 60 year old pin oak that is the same age as my house lives on for another 60 years is worth it.
Other Considerations in Choosing an Arborist
Whether an arborist is certified or not, it is a good idea to check that the arborist is insured. That is because if they or one of their crew is injured on your property, you as the property owner may be liable for any injuries that occur while tending to the trees on your property.
Also, as with hiring any professional for home repairs or improvements, it’s important to check their references or get recommendations from colleagues and friends. You should also check whether your local government has any regulations on tree management within city limits. If so, be sure that who you hire has experience with following those regulations, and has all of the business registrations and approval from the local government.
It is also important what your needs are. If you need a large specimen tree pruned and the potential for tree injury or death would be devastating, then hiring someone with documented expertise is important. If you’re instead just trying to get the half-dead tree in the back yard chopped down and there’s no risk of falling a tree onto a power line or structure, then documented expertise might be less important (though insurance might be, see above).
In addition, if you are getting a large tree taken down, consider the value of the wood in your tree. Large hardwood trees may have significant value. Some tree guys will offer to take it down for free in exchange for the wood. While this may sound like a good deal, I know people who were shorted thousands of dollars from such transactions when considering the value of the wood and the per hour cost of an arborist.
Type of Credential: Professional Certificate
Both the RCA and ISA Certified Arborist credentials are considered professional certificates. This means that these are optional credentials. Arborists are not required by law to be certified. This means that an arborist can operate without certification. Arborists that are certified have had their credentials reviewed, and meet or abide by the criteria described below.
Education and Professional Experience Requirements
Registered Consulting Arborists must be a current ASCA member, and be a graduate of the ASCA’s Consulting Academy (ASCA, 2019b). No additional education or work experience is required.
ISA Certified Arborist must have three or more years of experience in arboriculture and/or a degree in the field of arboriculture, horticulture, landscape architecture, or forestry from an accredited institution of higher education (ISA, 2019b).
Registered Consulting Arborists must pass an open-book exam as part of the ASCA’s Consulting Academy, which also includes other assignments before, during, and after the academy (ASCA, 2019c).
ISA Certified Arborists must pass a qualifying exam (ISA, 2018).
Code of Ethics
The ISA Certified Arborist program has a code of ethics that all certified arborists must abide by (ISA, 2019c). The RCA program does not have a code of ethics.
Registered Consulting Arborists must complete 420 continuing education units (CEUs) to be eligible for the RCA credential (ASCA, 2019b). Their website does not specify if additional CEUs are required in order to maintain the RCA credential.
ISA Certified Arborists are required to complete 30 CEUs in a three-year period in order to maintain their certification (ISA, 2019d).
ASCA. 2019a. The RCA. American Society of Consulting Arborists. https://www.asca-consultants.org/page/RCA (accessed 25 September 2019).
ASCA. 2019b. Eligibility/Fees. American Society of Consulting Arborists. https://www.asca-consultants.org/page/EligibilityFeesRCAs (accessed 25 September 2019).
ASCA. 2019c. ASCA’s Consulting Academy. American Society of Consulting Arborists. https://www.asca-consultants.org/page/ConsultingAcademy (accessed 25 September 2019).
ISA. 2018. ISA Certified Arborist Application Guide. https://www.isa-arbor.com/Portals/0/Assets/PDF/Certification-Applications/cert-Application-Certified-Arborist.pdf.
ISA. 2019a. Types of Credentials. International Society of Arboriculture. https://www.isa-arbor.com/Credentials/Which-Credential-is-Right-for-You (accessed 25 September 2019).
ISA. 2019b. ISA Certified Arborist. International Society of Arboriculture. https://www.isa-arbor.com/Credentials/Types-of-Credentials/ISA-Certified-Arborist (accessed 25 September 2019).
ISA. 2019c. Code of Ethics. International Society of Arboriculture. https://www.isa-arbor.com/Credentials/ISA-Ethics-and-Integrity/Code-of-Ethics (accessed 25 September 2019).
ISA. 2019d. Maintaining Credentials. International Society of Arboriculture. https://www.isa-arbor.com/Credentials/Maintaining-Credentials (accessed 25 September 2019).
Merriam-Webster. 2019a. Definition of Arboriculture. Merriam-Webster. https://www.merriam-webster.com/dictionary/arboriculture (accessed 25 September 2019).
Merriam-Webster. 2019b. Definition of Arborist. Merriam-Webster. https://www.merriam-webster.com/dictionary/arborist (accessed 25 September 2019).
Gardeners are assaulted with marketing campaigns nowhere better than in the fertilizer aisle of a garden center. There are so many choices and the labels suggest that fertilizing garden plants is a complicated process that requires specialized products.
Laws require that fertilizers list the proportion of the most important macronutrients on the front of the bag. Nitrogen, Phosphorus and Potassium abbreviated N, P, K, respectively, will always be shown with the ratio of their concentrations such as 5-10-15. This indicates the bag contains 5% nitrogen, 10% phosphorus and 15% potassium. The bag will also specify the weight of fertilizer contained in it, usually in pounds here in the United States. Of course, labeling requirements vary in other countries. Since fertilizers are not drugs or pesticides the labeling requirements are relatively lax and thus are open to extensive marketing. With fertilizers, as long as the contents are labeled and the proportion of N P and K are somewhere on the bag, any other claim can seemingly be made.
For years fertilizers have been designed specifically for certain plants. You can commonly purchase citrus food, camellia and azalea food, vegetable fertilizer, and of course turfgrass fertilizers which have been widely marketed for decades. Some fertilizer blends are based on research. Turfgrasses have a high requirement for both Nitrogen and Potassium and you often see elevated percentages of these in turfgrass fertilizers. Palms also require more potassium than Phosphorus and products have been developed that are “palm special” fertilizers. Despite all the research, manufacturers still throw in some phosphorus even though phosphorus is abundant in the United states in most soils. It is not clear to me what makes citrus food different from any other fertilizer, although claims that it is best for citrus can usually be found on the product. We grow more citrus in Ventura County, particularly lemons than anywhere in California, but none of the growers apply “citrus food”.
Some fertilizers are marketed for acid loving plants. Acid forming fertilizers have the ability to temporarily reduce pH in media or soil to which they are applied. This is because they have a high amount of ammonium or urea as the nitrogen source. Microbes in soil oxidize the nitrogen to nitrate and release hydrogen ions that make the soil more acid. Continual use of acid forming fertilizers can drop soil pH to dangerously low levels and make nutrients unavailable to many plants. This is especially the case in high rainfall climates where mineral nutrients are easily leached from soil. Another product often used to lower pH is aluminum sulfate. Often marketed as “hydrangea food” it helps to promote blue flowers in this plant. Special care should be given here as aluminum can easily be applied to toxic levels.
For as long as fertilizers have been sold they have been marketed as products that make plants grow better. When the importance of mycorrhizae were discovered, manufacturers found a new marketing angle that could be used to sell fertilizers. Now countless manufacturers include mycorrhizal inoculants as part of their fertilizer blend. Not only are we able to feed the plant but we can also feed the soil with beneficial micro-organisms. This all sounds great but often the inoculant, if present in the bag, is not viable. In many cases garden soils already have plenty of mycorrhizal fungi in them so they really are not needed in fertilizer products. Other fertilizers include growth stimulants such as humic acid, fulvic acid or humates. Research does not support their efficacy in horticulture.
Fertilizer manufacturers feel that it is important that we gardeners use things that are “all natural”. I don’t know what is natural to you but for me it is natural to challenge claims that have no scientific basis. The very practice of fertilizing plants is NOT NATURAL! But the products are often purported to be. Sometimes natural is synonymous with organic. There are an amazing number of organic fertilizers, so much so that it becomes bewildering as to which one to choose. Organic fertilizers may or may not be ‘certified’ by an agency such as OMRI as meeting some standard. Generally speaking organic fertilizers are made from some carbon based source. They can be sourced as manures or as plant or animal based meals or products. The N-P-K ratios vary widely.
I am always careful to avoid manure-based organic fertilizer products as they can be unnecessarily salty. While many organic fertilizers may be rather “slow release” as they need to mineralize from organic to soluble forms, this is often not the case with manure based products which can easily burn plants if over-applied. Some organic fertilizers are made from rock like substances such as leonardite which are very slow releasers of nitrogen. These products are mined and are similar to coal but have fertilizer value. In trials I have conducted on containerized plants some of these products were top performers.
Another common type of organic fertilizer are the biosolids products such as Milorganite. These are processed sewage sludge products that are de-watered and made into fertilizer. They are very effective nitrogen sources. Some biosolids fertilizers have also been sources of metals, such as zinc, lead and cadmium. Metal contents are closely monitored by manufacturers but since these products come through municipal systems, zinc, copper and other metals such as lead are often elevated. Slow release and organic fertilizers are useful if they are applied with understanding of the mineral needs of the plants they are applied to.
Most plants grow fine without fertilization and the main fertilizer element that plants respond to is nitrogen. So despite all the marketing claims seen on fertilizer bags, a fertilizer with an adequate source of nitrogen will likely benefit plants in need of that element. Specialized fertilizers that promote flowers or roots are not substantiated by research. Elements other than nitrogen are usually not required and ratios of N P and K are not tuned for more blooms or more roots. Adding phosphorus to your fertilizer does not promote flowering unless your soil is deficient in phosphorus (a rare condition). Gardens in high rainfall areas will likely need more potassium and nitrogen, but Phosphorus is hardly ever limiting to plant growth. Most plants do not need or require special fertilizers but will respond to fertilizers that contain an element they and soils they are growing in are lacking.
For gardens that have a loam soil texture, little fertilizer will be needed. Soil types often determine fertilizer needs for plants. Sandy soils likely need the most fertilizer because they do not hold nutrients well. They are also the most likely soils to lead to pollution because fertilizer elements will leach easily. Plants growing in sandy soils are also at greatest risk from injury of overfertilization. Plants growing in clay soils are least likely to require fertilization because clays hold and retain cations so well. An informed way to fertilize your garden is to obtain a soils test and base your fertilizer program on the results you obtain. For more on technical details of fertilizing see John Porter’s column in this blog archive.
When you think you need to fertilize garden plants follow these suggestions:
-Base your fertilizer program on a soils test
-Fertilize sandy soils more frequently than clay soils but with smaller amounts
-Most gardens require some nitrogen but not Phosphorus or Potassium so look for NPK ratios with X-0-0 as these products will only supply nitrogen.
-Some plants such as palms and turfgrass benefit from potassium so use a product with X-0-X
-Do not fertilize at planting time, wait until plants establish
-Always apply water after applying soluble fertilizers so they are dissolved
-If using Organic fertilizers chose one with a higher N content
-Never over-fertilize. Landscape fertilization can impair natural waterways resulting in algal blooms that kill fish and other aquatic life.
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 – 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.
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.
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 will
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.
Bassuk, N. 1994. A review of the effects of soil compaction and amelioration treatments on landscape trees. Journal of Arboriculture 20:9-17.
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
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.
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).
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).
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.
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.
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 Asian Delight Pak Choi – this was planted in May and didn’t bolt. We were still harvesting it in October.
Pepper Just Sweet – these plants were big and healthy even when everything else was struggling. The peppers were delicious.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
-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.
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.
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.
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.
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.
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.
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.
But while the trees didn’t survive, the burlap, wire basket, and webbing were all still there almost 30 years later.
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.
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.