From toxicity mitigation to drought tolerance, mycorrhizal relationships between plants and fungi stand to benefit growers as an easy production choice for their nursery crops. We caught up with Scott Inman, Director of R&D, Regulatory, and Facilities at Mycorrhizal Applications, to learn some of the benefits of using mycorrhizal fungi.
How can mycorrhizal fungi help growers maximize nutrient uptake and overall plant nutrition?
The symbiotic relationship between the plant and the mycorrhizal fungi maximizes nutrient uptake because the mycorrhizae create a hyphal network (a.k.a. mycelium) within the root zone that has the ability to capture nutrients in the growing media or soil that are otherwise unavailable to the plant. The mycorrhizal hyphae effectively increase the absorptive surface area of the roots (50x) by acting as a living extension and capturing more of the nutrients applied by the grower, so less fertilizer gets flushed through the pots. Mycorrhizae also have the ability to capture both the bioavailable and tightly bound forms of the nutrients by solubilizing unavailable forms of key nutrients and delivering them directly to the plant. The mycorrhizae provide nutrients to the plant in exchange for carbon, and growers benefit from this fundamental symbiosis in the form of nutrient efficiency.
How can mycorrhizae help plants become more drought-tolerant?
The mycorrhizal mycelial network actively sources and delivers water directly to the plant and has different mechanisms to support a plant’s drought tolerance. The mycelium’s hyphal strands have the ability to absorb water along the entire length of their hyphae and deliver it directly to the plant’s vascular system, increasing absorptive surface area. The hyphae are a lot smaller than roots and can penetrate pore spaces that the root cannot. And most importantly for drought tolerance, the mycorrhizae can store water for times of drought, both within the mycelium itself, which stores water like a sponge, but also in structures called vesicles that endomycorrhizae form within the root cells which store liquid in the form of lipids that the plant can access in times of need.
During times of extended drought stress, the plant is able to be much more efficient overall because it doesn’t need to invest as much in root growth to try to locate additional water in the rhizosphere. The mycorrhizae is investing in doing the growing, using the carbon that the plant provides in exchange for water and nutrients. Therefore, the plant doesn’t have to expend the same amount of energy when resources are scarce, once that mycorrhizae association has already been developed, and it has access to the assistance provided by the symbiotic fungal partner.
How can mycorrhizae mitigate toxic soils? What are some other soil health benefits?
In this drought trial, on average the MycoApply treated plants were able to withstand wilt for 24-36 hours longer between watering intervals. The coreopsis on the right was treated with MycoApply and the plant on the left was untreated.
Photo courtesy of Mycorrhizal Applications
Mycorrhizae can grow, penetrate, and colonize plants in different soils and filter out toxic elements to protect their plant partners. The mycorrhizae absorb the toxic elements such as heavy metals or sodium, which may have been present in the water or in the soil/media, and the fungi will hold the toxic elements, and then transport the beneficial nutrients and water to the plant. You end up with a plant that actually can function and be productive in conditions that otherwise would be toxic, due to this buffering effect of the mycorrhizae.
What should growers know about application for the best outcome?
The key to the best outcome is simple: just make sure that the mycorrhizal inoculant gets applied in a way that puts the active ingredients directly into the root zone, because that is where the symbiotic relationship is formed. Once growers get it into their root zone, the plant will drive the relationship based on its needs.
With our MycoApply line of professional inoculants, growers have a diverse array of efficient application options, including soil/media incorporation, soil drench, plug/propagation tray drench, drip irrigation, boom spray, bare root treatment, and many more.
As a grower, you’re looking for growing media that can elevate your crop production process, not complicate it. Frederic Gagnon, Lambert Peat Moss agronomist, tells us how Lambert develops consistent mixes that growers trust.
How does peat quality affect the success a nursery has with its growing media?
Peat quality can make the difference between a very successful crop or an average one. It is the base of your production, the foundation. You can try to correct or improve a so-so quality peat by adding a lot of perlite or other components, but the base will remain the weak point. A great quality peat will provide you with a mix structure that will provide lot of porosity/air space. It becomes possible when the harvest is well done by conserving the peat fibers’ integrity, so less dust or fine particles are created. Those fine particles will not add any mix volume because they are hiding in the air space, reducing it.
What steps does Lambert take to improve peat quality?
We focus on the harvest procedures. That’s the first step and it’s very critical as this raw peat will be your material to work with. You need to put a lot of care into preparing the field for harvest and always keep an eye on the weather forecast. The decision to go out in the field to do some preparation work should be done when you can reasonably predict a harvest period. It’s evident that nobody can predict a unexpected thunderstorm that will ruin your preparation work (forcing you to do it again and breaking fibers), but it’s always wise to play safe.
Photos courtesy Lambert Peat Moss
How does Lambert ensure consistency in each type of mix it produces?
The consistency is for sure the main point of a quality control department. Producing a consistent product from batch to batch is always very appreciated by customers. They can rely on a recipe that they applied before and can expect the same results. We have technical specifications for all the mixes and no products leave our yard if some criteria are out of the required ranges. It’s insurance for the growers that chemical and physical characteristics are as expected when the order was placed.
How does Lambert work with growers to help them determine the right type of mix for their needs?
We discuss it with them; that’s the first thing. Production management, container sizes and types, locations, etc. are different points that influence the recommendation that will be made. You cannot only focus on the crop as Texas and the Northeast U.S., for example, will not necessary require the same mix in wintertime! You need to know how a new customer’s greenhouse is set or if a long-time customer makes some changes and needs something slightly different. Communication is very important.
Consistent containers: With 29 years in the nursery and greenhouse industry, Tom Brewer, sales manager at The HC Companies, shares insight on the companies’ growing containers.
Since 1986, The HC Companies has produced an array of horticulture plastic containers. But as growers and equipment continues to evolve, the company has adapted its products accordingly, and offers containers that work well with automated processes. Sales manager Tom Brewer shares insight on those automation-based containers and how they can enhance your production process.
What type of containers does The HC Companies sell?
We have containers which work well in greenhouse and nursery production. We manufacture containers for large growers cultivating crops to sell to either independent garden centers or to big-box retail garden centers like Walmart, Lowe’s, Home Depot, Kroger and Costco for example, as well as smaller growers who service their own retail operations. Our nursery containers are made in a few different ways: The injection-molded containers — available in #1, 2, 3 ,5, 7, 10, 15 and 20 trade sizes — are heavy-duty plastic pots that many times are floor stacked in truck trailers. These are used by growers who are shipping their product across country. The thermoformed pots — available in #1, 2, 3 and 5 sizes — are lighter than the injection containers but will still do well in outdoor, long crop production cycles. The more economical pot is the blow-molded container that is similar to thermoform, but can come in larger sizes like 25, 45 and 65 gallons.
What’s the difference between the round, tray, flat and sheet containers other than shape?
It really depends on the growers’ unique market and what specific plant varieties are going to be grown in the container. If it’s for a bedding plant, growers can use a tray pack. Examples include impatiens, petunias or marigolds, plants which can be grown in a rectangular shaped tray for packs. The more premium plants can go into the larger round containers, which would be azaleas or premium vegetative type plants like Supertunias, or a lot of varieties that are sought after. But it really depends on what the nursery or greenhouse growers’ specialty is, and HC will match the container to their need.
How has The HC Companies adapted its products to automation?
When we talk about automation, we’re looking for ways to reduce touch. The whole mantra of the grower is, “How can I eliminate the handling of someone picking things up at point A and moving it to point B? How can we streamline that process?” As nurseries and greenhouses move forward, they are looking for ways to use systems — conveyor systems, forking systems or any kind of system that will reduce the amount of times people handle material. The HC Companies has containers suitable for different applications. We have easily de-stacked pots which will work with de-stacking equipment; we also have a series of square press fit pots and trays where growers can take an empty flat and press it onto a stack of pots. We are always looking for ways to make containers that will match those systems.
Why should growers consider The HC Companies for their container needs?
HC is a combination of many storied brands. We have a large, national network of sales reps which means there’s someone in nearly every region who can visit the nursery and actually look at what the application is in order to make a suggestion. All of our containers are made here in the United States, and we work with some great distributors. Over the years, I’ve also noticed that nurseries and greenhouses are always looking for something new, so we try to keep our finger on that pulse continuously.
Keep it covered: A thorough, post-season examination of growing structures will likely save expenses and improve crop performance for the following year.
Whether it’s a simple poly house or a more complex greenhouse structure, annual inspections and year-end maintenance tasks are critical. Chris Kirschner, regional sales manager at Atlas Manufacturing, describes what to look for and what to consider before the next growing season.
What are some important steps to take before buttoning up an overwintering structure?
Boots on the ground, eyes on the greenhouse! Look at your buildings with a walk around looking at the outside of the building but also inside looking out. Are there gaps around shutters or vents, doors or openings? Are there holes in your covering? Now is the time to order your poly patch tape to make any repairs. Check to make sure your poly inflation fan is working properly and order a spare. Are there places that need caulked to stop heat from leaking out or cold air from coming in? Check thermostats and heater and/or fan settings and make any necessary adjustments. This is also a great time to winterize or blow out water lines outside of the house.
What signs of wear on film determine that it’s time for a replacement?
No one really likes to fix something that’s not broke, but going into winter with covering that is marginal is not ideal. Inspect your covering closely. Overall, it may look fine, but look closely at the poly all the way around the perimeter. Everywhere the poly is held down by a fastener is a likely wear spot and could show some sings of tearing. Look closely at the poly where it crosses the structure’s framing, such as bows or purlins. Has it rubbed and turned gray? That “graying” could also be hiding small cracks or tears. Check the age of the covering. Keep updated records and consider using a Sharpie to write the install date somewhere on all your coverings. Try to use the same spot on every house if possible. A piece of poly film that looks fine but has been on for eight years needs to be replaced regardless of how it looks.
How significant is light transmission when it comes to film? How severely can the lack of light affect crops?
Light transmission is key. When trying to equate light transmission, on average, a rough idea of growth to light is equal. Therefore, just increasing your light transmission by 1-2% will give you an increase in plant growth of 1-2%. When you think of a double poly film covering having a light transmission range of 75-85% on average, discoloration or yellowing can greatly reduce this, which reduces plant growth. If you can increase plant growth by 5%, you might just pay for that new covering one year earlier.
When it comes to structures, in what instance(s) should growers not skimp on budget?
Do not skimp on loading and engineering. Never try to build a structure that doesn’t meet the snow and wind loads required for your area. You may have every intention of taking the covering off in the winter before storms, but in two or three years when the market has changed, you might need that space. If you’re going to take up precious land and put up a greenhouse, do it right and make sure that it’s versatile and will be able to react with changing markets and customer’s needs.
What are some structure upgrades that typical nursery growers should
consider? Just a few years ago, technology to remotely access and control your greenhouse was expensive and, in most cases, cost more than the average hoop house. Today that’s not the case. While you’re attending to other chores, crops, travelling, managing people or whatever your daily schedule demands, physically checking the temperature or manually turning equipment on or off just doesn’t add up. Technology now allows you to receive alerts when temps fall out of the parameters. You can adjust temperatures from your phone. You can regulate the watering or light cycle with the push of a button. Don’t get stuck in the dark ages. With automation, you’re not just saving time, you’re saving money and energy. By reading graphs and looking at your temps and energy use, you can make changes to optimize your efficiency. You’d be surprised at what little investment this can take.
Pine bark substrates ranging in age from fresh to 12 months.
Age affects us all. Some may think younger is better while others think age holds the key to wisdom and security. The same arguments could be made for pine bark substrate age and its effect on crop production management strategies. Over the decades, a lot has been speculated but very little has been proven regarding the physical, chemical, hydrological and biological effect that aging has on pine bark substrate materials. There are so many variables that factor into the investigation of age on organic materials and how other inputs, additives and biological entities interact and respond to these changing properties. As seen in the cover photo, age certainly has a visual influence on pine bark, but what changes are present that we cannot see? This article will highlight some of what has been studied in the past and present regarding changes in pine bark substrates.
FIG. 1 Pine bark arrives from sawmills to bark suppliers who process the material (A) before screening and windrowing (B) followed by turning and other management strategies (C) that accelerate the aging or composting process (D).
Pine bark may be used as a fresh, aged, or composted product. As my colleague Dr. James Altland (USDA scientist) has stated in some of his works, “there is no general agreement as to what constitutes fresh, aged, or composted when it comes to bark.” I agree with his assessment. What most believe to be acceptable (or at least workable) definitions would be that fresh bark has only been removed from freshly harvest logs for a short amount of time (days to few weeks) and has been processed to reduce its particle size suitable to be used in/as a substrate. Aged bark is bark that has been processed and often screened before being stacked/piled in windrows in open spaces and allowed to sit for a period of weeks to many months (Fig. 1). Aging bark does not include the addition of a nitrogen source to accelerate or enhance the degradation process. Aging piles may or may not be frequently turned (aerated) or managed in other ways. Composting bark includes the addition of a nitrogen source and the controlled turning and management of piles/windrows to speed the degradation process as much as possible in efforts to stabilize the bark material. The majority of pine bark supplies in the Southeastern U.S. are aged and not composted, but some proper composting operations do exist. For the purpose of this article, as well as most published works on the topic, bark will be referred to as fresh and aged (not composted).
FIG. 2 Fresh bark has a characteristic orange-tan color (A) and can be processed in various particle sizes and shapes while aged bark (B) has a darker color and typically has a smaller particle sizes due to aging.
Fresh and aged bark materials that can be found at numerous bark suppliers and can range in color, particle size and shape, as well as smell and chemical composition as seen in Figure 2. While both aged and fresh pine bark can be used successfully, little research has been done to investigate the differences between fresh and aged materials, as well as pine bark of specific ages. Additionally, the actual age of pine bark used for research in the literature is usually not reported, making it hard to extrapolate anything more than general trends for bark that is considered “aged.” To gain a greater understanding of the effects of aging and pile management on pine bark substrates, a 12-month study was conducted at a pine bark supplier in Eagle Springs, North Carolina, which included replicated windrows of specifically processed, screened, and monitored bark inventories (Fig. 3). This long-term project was initiated with the objectives of tracking and quantifying the chemical, physical, hydrological and biological changes that occur over time in bark materials. At each month, these bark piles were methodically sampled and analyzed. Some of the monthly tests included sand content (contamination from the wind and from the act of turning the bark piles every month; Fig. 4A), pH (Fig. 4B), and seedling germination trials as a method to detect bark phytotoxicity (Fig. 4C-D). In this article we will highlight only some findings from the pH and PGR trials conducted on some of the bark ages.
FIG. 3 Pine bark aging study shown in experimental windrows at T.H. Blue Inc., a pine bark supplier in Eagle Springs, North Carolina.
Nitrogen
A thorough search through the published scientific literature only provides a few papers that summarize experiments investigating nitrogen use/tie-up of fresh or aged pine bark during crop production. Studies dating back to 1979 through 2008 that evaluated numerous woody plant species under various growing conditions reported that nitrogen was not the limiting factor in any plant growth differences that were observed when plants were grown in fresh or aged pine bark. These reports, a total of seven, associate the growth differences found in their studies to irrigation management, bark particle size, plant available water, or some degree of early onset phytotoxic effect from fresh bark on young plant growth. The nitrogen fertilization trials conducted were not very through in covering a wide range of bark ages but instead most only compared fresh bark to barks aged for many months or even years. However, when no convincing scientific evidence can be found in the literature to suggest a significant immobilization of nitrogen by fresh bark to the extent of it negatively affecting plant growth, it is worth noting. Until some definitive evidence is provided, there seems to be little concern of nutrient management issues for growers who may choose (or have to) use fresh bark.
pH
FIG. 4 Testing of aged pine bark materials included (A) assessment of sand contamination, (B) pH, and (C-D) seedling germination screening for phytotoxicity.
Pine bark is highly acidic, with a pH range generally between 3.8 to 4.5. Several sources disagree whether the pH goes up or down with aging and/or decomposition, which may be due to the fact that pH may decrease if bark piles are improperly managed and have gone under anaerobic conditions during the aging process. Other researchers have found no changes in pine bark pH based on age, while some have indicated that there may be an increase in pH when the bark has a higher percentage of fine particles. To better understand the effect that age has on pH and pH response in pine bark a study was conducted where samples of pine bark aged for 0, 3, 6, 9, or 12 months were amended with various lime rates to investigate effects of pine bark age on lime efficacy. Pulverized 100 mesh dolomitic limestone was incorporated at rates of 0, 4 and 8 lbs/yd3. On 1, 3, 5, 7, 14 and 21 days after limestone amendment pH was measured using the 1:1 extraction method. We found that pH increased rapidly one day after lime addition, with slight increases during days 3 through 5, and a general stabilization for the remainder of the sample days (Fig. 5). Lime had the greatest pH response in fresh bark (0 month) at both the 4- and 8-pound rates compared to older barks. As bark age increased there tended to be a lower pH response to lime additions, possibly due to chemical changes in the bark over time that increased its ability to buffer pH change. If growers choose to grow in fresher bark, management of pH should be monitored closely both in pre-plant lime additions and during crop production.
FIG. 5 pH response of pine bark substrate at ages 0, 3, 6, 9, or 12 months to rates of limestone additions.
PGRs
The application of plant growth regulators (PGRs) to control excessive growth, and increase marketability, of containerized crops is common practice in the horticulture industry. The primary benefit of PGRs is to allow the production of compact, uniform crops, that can be more tightly spaced in the growing area. One of the most common application methods of PGRs are substrate drenches. One of the concerns with drench applications is adsorption of active ingredient by organic substrate components. Previous works over the decades have shown that pine bark in substrates can reduce the efficacy (growth control) of PGRs. With pine bark being a common substrate component and age of pine bark possibly differing among suppliers, more scientific data was needed to describe differences between ages and management practices that can maximize effectiveness of the substrate at these different ages. Although studies have investigated different variables that may influence PGR efficacy in pine bark substrates including percent incorporation, bark particle size, and fresh versus composted pine bark, no information was available on the effects of pine bark age on PGR efficacy.
A project in 2017 amended pine bark aged for varying lengths of time with Canadian sphagnum peat at ratios of 60:20 and 40:40% (v:v) peat: pine bark, with the remaining 20% being perlite. Substrate blends were fluffed and wetted by hand to a moisture content of 60% prior to pH adjustment and potting. A control substrate blend of 80:20 (v:v) peat: perlite was also included. Marigold and sunflower plugs were transplanted into 12.7cm azalea containers and plants were fertilized twice a day at each watering with 150 ppm nitrogen from a water-soluble fertilizer. Twenty days after planting, 3 fl oz of solution containing either 0, 1, 2, or 4 mg of active ingredient (a.i.) per container paclobutrazol (Piccolo 10XC; Fine Americas Inc., Walnut Creek, California) was applied to each container as a substrate drench. The experiment was a completely randomized design with six replications of six substrates x four PGR concentration combinations. Although not always significant across all PGR rates, there was a general trend of reduced growth control with increasing age of pine bark as seen in the 40% bark inclusion rate at the highest rate of PGR application (Fig. 6). Not shown are the plants grown with 0 PGR application which showed minimal growth differences which supports what we see in Figure 6 to be a result of the PGR and not a major growth retarding influence of fresh bark on the growth of these two species. This data indicate aged bark may cause a greater reduction in drench applied PGR efficacy (reduced growth control) compared to fresh bark but it is unclear if it is the bark chemistry, particle size, or other variable affecting the PGR growth control response.
Bark age does seem to have some effect on various plant growth parameters and cultural management strategies, but the effects do not appear to be greatly inhibiting or difficult to address. Based on the literature over the past four decades, pine bark age does not greatly influence nitrogen or other nutrient regimes but it may offer challenges to irrigation (plant available water) or other chemical applications like pH or PGRs in certain crop production systems. Bottom line, as long as pine bark is not toxic, which most all accounts show that it is not unless growing seedlings or herbaceous plants in very fresh bark with small particle sizes, crops can be grown in any age of pine bark with no serious detriment as long as adjustments are made where needed. When growers factor in the cost differences of fresh versus aged bark (including volume delivered per truck and overall transportation costs) compared to the costs associated with managing crops in fresh pine bark there may be some changes that make sense/cents. As always, it is suggested to have conversations with bark suppliers or other knowledgeable substrate experts to explore options before deciding to convert entire operations to bark you are not used to.
Brian Jackson is an associate professor and director of the Horticultural Substrates Laboratory at North Carolina State University (Brian_Jackson@ncsu.edu). Laura Barth is a former graduate student.
FIG. 6 The influence of 4.0 mg of active ingredient Piccolo on (A) sunflowers and (B) marigolds grown in peat-lite (left) and peat substrates containing 40% pine bark aged (from left to right beginning with second pot) 0, 3, 6, 9, or 12 months.
