Posted by sustainable_hort on December 23, 2009
The following is an excerpt of an article published in this year’s Cenflo, Inc.’s Nursery BooK…
What do we mean when we say “sustainable?” It is becoming almost as vague as the definition of “green.” This obviously means both more efficient energy and water use, and production methods that move toward “organic.” Not necessarily “organic,” but the use of less toxic pesticides, fungicides and herbicides, finding alternatives to plastics, and replacing petroleum-based fertilizers.
The simplest answer seems to be one published in the ATTRA guide to Sustainable Small-Scale Nursery Production. It states the following:
“Sustainable nursery practices aim to reduce levels of synthetic fertilizers and pesticides, use integrated pest management systems to deal with insects, diseases and weeds and focus on building the soil to promote plant health.”
Granted, much of the energy nurseries are expending moving toward sustainability is about energy. This is a key consideration, since energy use in our industry, especially in greenhouses, has room for significant improvement [both in how it is generated and how is used]. In fact, much has already been written and discussed on this topic.
Water is another sustainable issue. But, nurseries have had to deal with it for more than a decade and with recycling technologies, many strides have been made to make it one of the bright stops, one of the success stories for the industry.
But, the other production technologies…fertilizing, pest and disease control, how we actually grow our plants…has received much less consideration. But, it is equally important, and to the consumer, ultimately more important. In fact, consumers are actually demanding products that are produced sustainability. Demand for organic vegetable and herb starts has exploded, with annuals and perennials seeing a similar increase. If someone had said there would be consumer demand for trees and shrubs, even I would have expressed serious doubt even just a few years ago.
SOME COMMON SUSTAINABLE STRATEGIES
While some sustainable technologies will require nurseries to make major changes in the production practices, many are already being used by growers. Some of these include the following:
• Better Soil Media
While it is not as crucial an issue in field production, container media is often far removed from natural soils. Some research has indicated this may actually be leading to some disease and pest problems. The book Healthy Crops addresses this issue. It looks extensively at 75 years of plant research and argues that over use of nitrogen and certain applied pesticides actually change the plant’s physiology and makes them more attractive to pests and susceptible to disease (??).
Over the past decade, many more soil products have become available that could limit these detrimental affects. One simple strategy for growers is to look for commercial products that are used in organic production with labels stating they are “OMRI Listed.” OMRI is the Organic Materials Review Institute, a nonprofit organization that evaluates products and processes for the organic industry. Their listed, reviewed products meet the requirements of the National Organic Standard.
Or growers can mix their own container soil mixes using recipes found in ATTRA’s Potting Mixes for Certified Organic Production and other published literature;
For example, one suggested substitute recipe is as follows:
Organic substitute for Cornell Mix
• I cu. yd. sphagnum peat
• 1 cu. yd. vermiculite
• 10 lbs. bone meal
• 5 lbs. ground limestone
• 5 lbs. blood meal
Most published literature suggests first experimenting by making small batches and running them a careful evaluation. Larger nurseries probably have the equipment, space and labor for the mixing and storage their own mixes. Smaller operations can work with local soil mix producers to create their desired soils.
Ingredients that are generally allowed in organic media mixes include soil, sand, compost, sphagnum peat moss and other forms of peat, Coir dust, sawdust, and often use perlite and vermiculite, One of the most useful of these is compost.
Compost has become recognized as being beneficial for both the land and container soils. It acts as a soil conditioner, a fertilizer that adds vital humus or humic acids, and as a natural pesticide for soil.
“Well made composts can not only supply needed bulk to large container mediums, but essential physical characteristics to these blends that need qualities of aeration, porosity and drainage,” explains horticultural consultant Alison Kutz-Troutman, Sound Horticulture, Bellingham, Washington.
Thus, it provides a rich growing medium, or a porous, absorbent material that holds moisture and soluble minerals, providing the support and nutrients in which plants can flourish. She said it provides a range of nutrients over time in longer-term container cropping systems. She said it is rarely used alone, being primarily mixed with soil, sand, grit, bark chips, vermiculite, perlite, or clay granules to produce loam.
The actual amount in mixes varies greatly, and can range from 5% to 40%,” she said. “It is completely dependent on the compost chemistry analysis, physical characteristics, container size, and crop type and crop cycle.”
Meanwhile, microorganisms in good compost provide a wide range of biological services- from antibiotic-like activities to out competing disease causing organisms for food and space.
“While building a plant with bolstered immune system, growers experience greater efficiency and uptake of nutrients, which helps the bottom line,” she added.
For instance, Israeli researchers discovered that vegetable and herb seedlings raised in a mix of40% vermiculite, 30% peat moss, and 30% composted cow manure grew faster, with less incidence of disease, than those raised in a 40% vermiculite/60% peat moss mix.
Another example is using composted pine bark, a by-product of the
lumber industry, Mixes containing more than 20 percent composted pine bark were shown to support a significant level of suppression of Pythium damping-off. (30????).
But, Kutz-Troutman cautions that both consistency and availability remain limiting factors to wider nursery industry use.
“The availability of quality compost is becoming a limiting across North America and Europe,” she said, noting that there are even competing uses, such as methane digesters, that adds to the problem
Another cautionary note…some literature recommends not direct seeding into compost because it dries out quickly and may contain possible phytotoxins that could inhibit germination. Nitrogen can also be tied up by incompletely decomposed lignin.
Vermicompost is a type of compost that uses various species of worms, (red wigglers, white worms, and earthworms) to create a product commonly known as “worm castings.” This heterogeneous mixture of decomposing vegetable or food waste, bedding materials, is the end product of the breakdown of organic matter by worms.
It contains water-soluble nutrients and bacteria, and is an excellent, nutrient-rich organic fertilizer and soil conditioner. Other benefits include improving media’s physical structure, adds enzymes such as phosphatase and cellulase), and improves water holding capacity. The literature indicates the microbial activity in worm castings is 10 to 20 times higher than in the soil and organic matter that the worm ingests.
Vermicompost can be mixed directly into the soil, or leached in water and made into a worm tea. The resulting liquid is used as a soil fertilizer or sprayed on the plants.
Mycorrhizae, soil fungi that form beneficial associations with plant roots, help plant roots to do a better job of gaining nutrients and water. The fungi can be used in field or container production. Growers achieve better stand establishment, use less fertilizer and inoculate bare-root seedlings when using mycorrhizae. Commercially available mycorrhizae stimulate the roots of almost all tree and shrub species.
• Living Mulches for Field Production
Living mulches are cover crops planted between plant rows to hold the soil, provide traction, increase water infiltration and suppress weeds. The amount of nitrogen fertilizer applied each year by planting legume varieties. The use of these mulches, cover crops and applying composts in field production has been shown to improve nursery soil. Research has show that planting a diversity of crops and ones that attract beneficial insects improve the overall usefulness of these crops.
• Reduced Nitrogen Use
It has been the prevailing wisdom for many years that the more nitrogen the better. While it is true that research seemed to confirm that added nitrogen produced larger, possibly greener, plants, it did mean these plants were the healthiest ones, or survived better once they left the optimal nursery environment.
Again, Healthy Crops looked at the many effects of over-use of nitrogen and the possible negatives affects on plant health.
Then there is the issue of nitrogen run-off. In fact, research in Oregon showed that much of the nitrogen applied to containers was not used by the plants, but flowed out the bottom of the containers. The industry as a whole, but especially in container production, will need to continue to examine how much, and how, nitrogen is used in plant production.
• Organic Fertilizers
Luckily, there are numerous OMRI-approved fertilizers for growers to use. Granular sources tend provide nitrogen using ingredients such as alfalfa meal, blood
meal, bone meal, feather meal, fish waste, cottonseed meal, soybean meal and guano. Phosphorus sources include bone meal, shrimp wastes, guanos and rock phosphate. Greensand, granite meal, kelp meal and soybean meal all provide potassium.
Organic liquid fertilizers supply nitrogen through “fertigation” and include fish emulsion, fish powder, blood meal, bat guano, seabird guano, worm castings and composted manure teas. Some forms organic fertilizers work better with low-volume irrigation systems like drip or trickle systems. A 1992 study found that spray-dried
fish protein and poultry protein fertilizers do not clog drip emitters and micro sprinklers. Fish protein, blood protein, poultry protein and brewers yeast are all available as spray-dried materials, according the AATRA publication Sources of Organic Fertilizers and Amendments.
There is starting to be more evidence that a healthier plants will resist pest infestations more effectively that those that are grown with high nitrogen, and sprayed with various pesticides. Again, the book Healthy Crops addresses this issue, arguing that certain applied pesticides actually change the plant’s physiology and makes them more attractive to pests.
Pesticide use can also be reduced using the well-established practice of “integrated pest management.” This involves using resistant cultivars, building up populations of beneficial organisms, careful and consistent monitoring (“scouting”) of plants for pests numbers. Once pests are detected treatment thresholds are developed. If thresholds are reached then growers generally use spot treatments of pesticides that are the least harmful to beneficial organisms and the environment.
A key to this strategy is identifying pests early so appropriate measures can be applied quickly, while populations levels are low.
• Biological Control with Beneficial Insects
Biological pest control is a rapidly expanding field of agriculture, where natural predators are used to control many pests that causes economic harm plants in production. These methods using beneficial insects can be as alternatives or supplements to conventional pest control methods such as insecticides. Yet, is actually an older technology that was once a main control method in agriculture.
“Insectararies were much more common prior to World War I,” explains John Maurer, owner of Evergreen Growers Supply, Oregon City, Oregon. “Then, with development of DDT and other insecticides following the war, they almost disappeared.
He said the idea of beneficial insect control had started in the late 1800’s, when an introduced mealy bug from Australia nearly destroyed the US citrus industry. Researchers went to Australia, identified the pest’s natural predator, brought it back to the US, and began raising and releasing it in infested areas. It did its job and brought the pest under control.
But, it has taken many decades for growers to return to this environmentally sound technology. For years, growers saw it as expensive and ineffective, though that is rapidly changing, even a large operations such as Monrovia’s Oregon facility.
Monrovia Nursery’s Dayton, Oregon, operation has been testing and using beneficial for nearly a decade with increasing success. Monrovia’s pest control specialist Ron Tuckett has been using the predator mite Amblyseius fallacis for spruce spider mite control in Euonymus. After several years of use, he now rarely has to use any control spray to combat the pest.
“And, when we do use a control agent, we use the least toxic alternative (usually an oil or soap),”he said. “While it does kill both pest and predator, we have found the predator populations return faster, thus giving us good control of the pest.”
He cautioned that using benefcials does require careful scouting so the pests can be controlled at low population levels, more lead time in ordering, and at this point, does not work with every pest.
Maurer agrees and suggests growers start slow.
“Start small and take baby steps, since there will be successes and failures,” he said. “Over time, they will find that they will save time and money using beneficial over chemicals.”
“There is an economic advantage to using these beneficials,” agreed Tuckett. “The combined cost of the predator and any control compound (usually an oil) is definitely less than cost of the pesticides we used to use.”
Both pointed out that chemicals can also fail, and their continual use eventually can create resistance in the target pests. With a predator strategy, there is no resistance issue and the populations often build up over time, giving a grower continual control at a low cost.
• Organic pesticide control options
The more traditional approach of applying control compounds remains a common strategy. Numerous organic control products now exist for growers. Some of the companies include JH Biotech, Inc., BioWorks, Pharm Solutions Inc., Nature’s Solution,
Arbico Organics, Safer and many more.
• Compost tea
But, in the past decade, compost tea has gained a wider following in the organic community. It is a compost extract brewed with a microbial food source (molasses, kelp, rock dust, humic-fulvic acids, for example) and applied both to the soil and leaves (foliar). This brewing technique is an aerobic process that extracts and grows populations of beneficial microorganisms. The resulting “tea” also provides some nutrition to the plant or soil.
“Compost teas can be a very cost efficient means of delivering a liquid nutrient source into the crop system,” explained Kutz-Troutman.
She said conventional fertigation systems like drip need a little bit of special attention, but growers with overhead sprinkler systems or flood propagation areas can be very easily injected with these active biological materials.
One limitation is that the tea can be rapidly deactivated when foliar applied due to sunlight, rain and especially UV radiation. However, on the soil surface, the tea microbes effectively colonize plant litter and debris causing increases in the decay rates.
“Whether foliar treatment or soil drenches, the crop needs can be tailored to the objective of the grower,” she cautioned. .
“Unlike compost, as grower usage increases, we are finding many creative ways to meet volume needs across the nation,” she added.
• Reduced Herbicide Use
Weed control in modern field nursery production still remains largely based on the use of herbicides.
Yet, similar to fertilizers and pesticides, there are getting to be organic alternatives that are environmentally friendly contact herbicides that break down quickly. Some are strong vinegar-based compounds that contain acetic acid (vinegar), lemon juice, eugengol, thyme oil, orange oil and other natural ingredients. Nature’s Glory, Burnout and Bioganic are commercially available products.
Another class of products is made from pelargonic acid, a fatty acid found in plants and animals, including commercial products include Weed Eraser and Scythe, which rapidly lower the weeds’ pH level, weakening cell walls and killing the weeds within two hours.
Both classes work as contact herbicides, with varying degrees of success, so several applications may be necessary to kill perennial, broadleaf and grassy weeds. Application to nursery plants should be avoided
Corn gluten meal, a by-product of corn syrup processing, is another new pre-emergent herbicide. It is applied in early spring to the top one-quarter inch of soil. It must be reapplied every year and be very expensive when treating a large area. Another advantage is that it is 10 percent nitrogen, thus providing a slow-release fertilizer.
Corn gluten hydrosylate, made from corn gluten meal, is another new option that may be more effective controlling weeds and is applied at less than half the rate of corn gluten meal.
But, in organic food product, cultural controls are the first line of defense against weeds, including mechanical cultivation, flame weeding, mulches, living mulches, steam and solarization. Many of these are being tried in nurseries.
• Mechanical Cultivation
Monrovia Nursery has committed to an intensive hand weeding program. Their web site claims “our Plant Health Team weeds each of our 22 million plants by hand at our five growing locations, allowing us to reduce the amount of herbicides required.”
In 1991, Monrovia Nursery, with headquarters in Azusa, Calif., compared hand weeding to spraying herbicides and found that a combination of the two is the least-costly method Monrovia found it took workers 10 hours of hand weeding per acre, performed 10 times a year, to keep the nursery weed-free without using pre-emergent herbicides. By using a pre-emergent once in the spring and once in the fall, the workers only needed to perform hand weeding seven times a year, spending one hour weeding each acre. Monrovia paid workers $8 an hour, the cost of herbicide was $200 per acre per application and it took two hours to apply
• Flame weeding
Some nurseries have tried lame torches, or “flamers,” that sears and disrupts plant cells. As a flamer passes quickly over a weed it will kill the top, but roots can re-sprout new growth. This works better with broadleaf weeds than grassy weeds, which require a repeated flaming every two to three weeks.
Mulches exclude weeds by limiting the light reaching the seeds in the soil. They have an added advantage of retaining moisture in the soil. Organic mulches should be 3 to 4 inches thick and may need replenishing once or twice a year.
Researchers at Oregon State University tested mulches made of oyster shell,
Hazelnut shell and copper-treated geotextiles and found they provide good suppression of liverwort, one of the most challenging weeds to control.
• Fabric weed barrier disks
These disks, made of different fabrics, can control weeds in containers. They are slit to fit around the plant stem and sit on the soil surface. Weeds are prevented by growing in containers by excluding sunlight and inhibiting weed germination, while allowing air and water movement but prevent weed seed germination. They also reduce
evaporation. Some disks are even treated with inhibiting chemicals that prevent seeds that land them from germinating.
Research at Virginia Tech, chemically treated Geodiscs placed on container-grown willow oaks suppressed all weeds completely. Meanwhile, the trees grown in those pots had higher top dry weights and root dry weights than trees grown without any form of weed control and trees sprayed with a conventional herbicide. But, these types of products would not be considered organic.
Soil solarization can be used to kill pests or weeds before planting trees, shrubs or perennials. It involves stretching sheets of clear plastic over moist ground, which the soil and kills weed seeds and harmful insects, if summer temperatures climb high enough.
ON THE PATH
So, it seems that sustainability as a concept may be nebulous, but the specific strategies are becoming clearer. As more nurseries experiment and test these alternative technologies, there will be more successes. The old paradigm…”they are too costly or they don’t work”…is slowly being replaced by “let’s at least give it try.” As the petroleum-based fertilizers, pesticides and herbicides become more expensive, and, in some cases, less effective, the more natural or organic options become more economically viable. And that may eventually be the true sustainable aspect of these changes.
A special thanks to the National Sustainable Agriculture Information Service (formerly known at ATTRA), which has many useful publications for those interested in a more sustainable approach. Their website contains many useful publications. Those used in the article include:
• Potting Mixes for Certified Organic Production by George Kueppe, NCAT Agriculture Specialist and Kevin Everett, Program Intern, September 2004 ©NCAT 2004
• Sustainable Small-Scale Nursery Production by Steve Diver and
Lane Gree. Updated June 2008 by Katherine L. Adam, Agriculture Specialist ˝ 2008 NCAT.
• Sources of Organic Fertilizers and Amendments.by Andy Pressman NCAT Agriculture Specialist, February 2009.
• Overview of Cover Crops and Green Manures by Preston Sullivan
NCAT Agriculture Specialist, Published 2003, ATTRA Publication #IP024.
• Another useful resource is Fertile Soil by Robert Parnes (28), an in-depth publication on organic fertilizers. Parnes’ publication provides detailed tables on the nutrient content of various manures and plant and animal by-products. This work seems to be out-of-print. It had an original price of $39.95, but two copies recently listed on Amazon started at $164.00.
• Compost Teas for Plant Disease Control: Production, Application, and Results ASA-CSSA-SSSA Annual Meeting, Denver, CO, Nov. 5th, 2003 Steven Scheuerell and Walter Mahaffee, Department of Horticulture, Oregon State University.
• Healthy Crops, A New Agricultural Revolution. By Francis Chaboussou.. Jon Carpenter Publishing, Alder House, Market St.,lll Charlbury, England OX7 3PH.
•Optimizing nitrogen use efficiency of container-grown woodyornamental plants exhibiting various growth habits by Scagel C.F., Azarenko, A. N., Dept. of Horticulture, Oregon State University.
• Williams, Greg, and Pat Williams. 1998.Compost as a substitute for peat in seedling
grow mix. HortIdeas. December. p. 137.