In these uncertain times, many in our industry are concerned that consumers will forego spending money on landscapes to save money and water; yet, our urban green spaces are critical to keeping our cities cool and preventing further evaporation of our limited water supplies. The way I see it, we have a tremendous opportunity! We can either keep doing what we’re doing and risk losing our business… or, we can change the way we do business – using more sustainable products and processes, and marketing our sustainability to the consumer. There has never been a better time to be “green” and never more opportunity to educate consumers about resource conservation. I have been collaborating with a research group from Iowa State University. They are working on a process to manufacture biodegradable biorenewable nursery pots from abundant agricultural commodities such as soybeans or corn. They chose corn as the biorenewable source for production of their pots because of its superior properties that make it ideal for plant production. The product is still in the prototype stage but it has lots of potential for the industry. I’m presenting the concept to you today in hopes of hearing your ideas and feedback.
Rising costs of petroleum and negative consequences of disposing of petroleum-based plastic pots in landfills have led to increased interest in bioplastics. Conventional plastics are not biodegradable, and difficulties associated with the disposal of synthetic plastics used in horticulture have raised concerns about environmental sustainability. Recycling of nursery pots is limited because of a lacking infrastructure, poor resin quality, and ultraviolet degradation; therefore, most containers are deposited in landfills. The labor it takes to clean and reuse or to dispose of pots can be cost-prohibitive. And storage of old pots requires space and even more labor! So… many of our pots end up in landfills.
Synthetic plastics accounted for 26.8 million metric tons of municipal solid waste in the United States in 2006, only 7% of which was recycled.
The features you would want in a nursery pot include…..
The concept of biodegradable pots has been around for almost 30 years, since Jiffy made their pots made out of pressed peat moss. Since then, biodegradable pots have been made with coir (coy are) (coconut) fiber, fiber paper, wood fiber, sugar cane, palm fiber. These products work but they have an unpredictable longevity, high evaporative water loss, low strength limiting their use in plant production processes.
Relatively new, bioplastics technology has the advantages of….
Bioplastics are already in use for many kinds of products, including flexible and rigid food packaging and storage containers; disposable bottles, cups, and tableware; shopping and trash bags; films, screens and netting.
Most in the industry use the term bioplastic to mean a plastic produced from a biological source. One of the oldest plastics, cellulose film (cellophane), is made from wood cellulose. Not all bioplastics are biodegradable. All bio- and petroleum-based plastics are technically biodegradable, meaning they can be degraded by microbes under suitable conditions. However many degrade at such slow rates as to be considered non-biodegradable. Petroleum-based plastics can remain solid for hundreds of years. The degree of biodegradation varies with temperature, polymer stability, and available oxygen content. Japan has been a leader in this technology, incorporating them into electronics and automobiles.
Some not structurally sound enough to handle the rigors of plant handling and processing. Some bioplastics are mixed with conventional plastics to achieve certain desirable qualities. A disadvantage of this approach is that the products of degradation of the conventional material will remain in the environment for years. Currently, bioplastics are costlier to make than conventional plastics but an increase in supply will promise to reduce the cost and make it competitive with conventional plastics like polyethylene and polypropylene.
As I mentioned, this project is collaborative was started at Iowa State University by Drs. Bill Graves and Dave Grewell. Matt Helgeson is a graduate student working on the project. I am a collaborator and will be involved in testing the prototype in the arid climate and dry soils of Utah.
The pots are formulated from a corn protein called zein. It is processed from corn gluten, a byproduct of ethanol production. It has a long history of use dating all the way back to the early 1900’s where it was used for many things, including industrial coatings like shellac for flooring and furniture. Its only major current use is in the pharmaceutical and food industries for pill casings and for coatings on fruits and vegetables. Its hydrophobic properties make it an attractive bioplastic.
The raw material is powder that looks a lot like corn meal. This material is mixed with glycerol, which is used as a plasticizer, and ethanol, which is used to extract the zein.
Others have tried making pots from soybean, which is water-soluble -- it disintegrated rapidly when subjected to moisture. Zein pots are water-insoluble and will only degrade when placed in contact with soil. So, irrigating plants in these pots does not affect their degradation rate. Zein is 10% protein, which contains nitrogen. So, the group reasoned that it might release nitrogen as it degraded.
I’m going to share with you the results of some recent testing on the zein pots. Remember, these are just prototypes, and this testing is needed in order to refine the formulation of the pots to meet the requirements of efficient plant production. Initial tests were done with pots alone (no plants) to test the effects of substrate, irrigation, sterilization, and aeration on pot biodegradation.
Pots were filled with either a peat-moss-based substrate or with perlite and watered to field capacity every 2 days or every 4 days. They were held in growth chambers under consistent light and temperature for 73 days. Peat-pots and fiber pots were treated similarly and used for comparison.
Total nitrogen release in leachate from pots after 73 days. There were three treatment factors: pot type, substrate, and irrigation frequency. All four pot types were filled with either Fafard® 52 medium or perlite, and pots were irrigated with 200 ml of tap water either every 2 or 4 days. Treatments were arranged in a complete factorial combination resulting in a total of 16 treatments with three replicates per treatment. Pots were arranged in a completely randomized design in a growth chamber. The presence of peat moss enhanced microbial degradation of zein. Although not shown here, increased frequency of irrigation inhibited zein degradation, probably due to lack of oxygen for microbial action. Biodegradation of pots requires a substrate (zein) and a source of microbes. Peat and fiber pots showed few signs of degradation – there was a source of microbes but no substrate for them to degrade.
In the second experiment with pots, all pots were filled with a peat-based substrate, and each filled pot was planted individually into a larger conventional plastic container filled with field soil to simulate the protocol of installing a plant in the ground with the bioplastic pot in which it was produced. The larger containers either were allowed to drain after irrigations or were kept saturated. For half of these two-pot experimental units, both the Fafard® 52 and soil were sterilized (autoclaved) immediately before use, whereas nonsterilized Fafard® mix and soil were used for the other half of the units.
Placement of bioplastic pots into soil, which was intended to simulate the possible practice of transplanting or installing without pot removal, led to more weight loss when the soil was drained than when the soil was saturated. In drained soils, the bioplastic degraded extensively and lost structure and shape, whereas pots in saturated soil, though misshapen, remained intact. Use of sterilized substrate did not influence weight loss of the pots. Peat pots formed mold on their outer walls.
Finally, our evidence that pots made from zein release nitrogen justifies further studies to explore how nitrogen from these pots may benefit plant growth during production, may reduce the need to apply nitrogen fertilizers, and may aid establishment of crops transplanted or installed with their pots.
Next, it was time to find out how plants would respond to zein pots under growing conditions.
Here is a study where they grew geraniums in three types of pots, zein bioplastic, regular plastic, and jiffy peat pots. Plants were grown in the greenhouse in the 4” round pots for 7 weeks. After 7 weeks, the plants were transplanted into 8” azalea pots. Treatment- Half of the reps were removed from the original pots prior to transplanting, and the other half were transplanted in their original pots to simulate planting in the ground with the pot. After 6 weeks we found that plants kept in their zein pot were not performing as well as those transplanted without the zein pot. Above is a comparison of a plant removed from the zein pot (left) and a plant kept in the zein pot (right) As you can see the growth is very reduced in the plants kept in the zein pot. We suspected that ammonium released from the degrading pot (mineralization) was so high that it is becoming toxic, but we had to rule out root restriction as a cause of reduced growth.
So, geraniums were grown for 7 weeks in either plastic pots, peat pots, or zein pots. Then they were transplanted to a plastic outer pot without removing the original pot and grown for another 6 weeks. Here we see that plants kept in plastic and peat pots are doing much better than in zein. So something other than root restriction is limiting plant growth in zein pots. Both pictures from left to right – Geranium in plastic pot, geranium in peat pot, geranium in zein pot
Whether the plants are transplanted with or without pots doesn’t influence root growth – except those transplanted with the zein pot. Notice zein pot is degrading but roots are not growing – something is limiting root growth in zein pots. R = pot removed prior to transplant; k = pot kept in place during transplant. Now they began to suspect that something toxic was being released during the zein pot degradation.
Here is a close-up of the zein pot. It’s clearly not root restriction because you can see that much of the zein pot wall has degraded. Roots in the peat pots are growing through the side walls.
This is a very interesting graph. Six weeks after transplanting, they saw a huge increase in ammonia levels in the leachate from zein bioplastic pots (mineralization of the protein). They saw no ammonium in the plastic pots. Neither type of pots received any ammonium from the liquid fertilizer (Hoagland’s #1). Note that this is way more ammonium than would ever be applied to any plant. Our next goal is to find a way to reduce this ammonium output!
EC is electrical conductivity. It is a measure of how much salts are present. Since fertilizers are simply chemical salts, too much fertilizer can increase electrical conductivity above the safe zone for plants. (Most plants do best with EC below 3 or 4.) You can see that whether or not supplemental N was provided, the zein pots released toxic levels of salts to the planting substrate.
A ray of hope! After 6 more weeks, however, roots began to grow through their zein pots and plant growth started to catch up to that of plants not transplanted in zein pots. Plant in zein pot on left, plant out of zein pot on right. More growth of the plant in zein pot compared to the first harvest (see slide 2), but still not caught up to plants removed from the pot.
In another study they looked at the nitrogen release capacity of the pots. They used two pot types and two fertility treatments. Pots were plastic and zein. Fertility treatments were Hoagland’s with nitrogen and Hoagland’s without nitrogen We found that plants in plastic pots became deficient without nitrogen, but plants in zein pots did not. In the leachate they measured significant levels of ammonium and nitrate in the zein pots that didn’t receive any nitrogen. This is good, but we also found that all plants in zein pots did not perform as well as plants in plastic that were provided nitrogen – notice the small leaves
These are problems inherent with the used of a protein-based pot, but they are not insurmountable problems. There is reason for hope! Plants in zein pots may be able to be transplanted directly into the landscape, pot and all, and show greater vigor because of the nitrogen provided during pot degradation. Now the problem is to adjust the pot formulation to slow down the release of nitrogen.
Corn stover is the leftover parts of the corn plant that, today, are not directly used to produce ethanol.
As currently formulated… longevity of about 3 months under greenhouse conditions. Hopefully, modifications in pot design or composition promise to expand the range of crops that can be produced in these containers.
Bioplastic Nursery Pots for Profitability and Sustainability
Ornamental Horticulture Specialist
Utah State University Extension
Synthetic plastics are petroleum-based
Recycling is limited
Pots accumulate in landfills
Hold up to moisture
Decomposed by naturally occurring
Reduce dependence on foreign crude oil
Reduce emissions of greenhouse gases
Produced from byproducts of agricultural
First bioplastic: cellulose film
Bioplastics made from corn, wheat, or
Standards for biodegradability:
• 60% biodegradation within 180 days (ASTM
6400) – U.S. standard
• 90% biodegradation within 90 days (EN 13432) –
Most made from sugars or starch (water-
Some not structurally strong
May leave residue when degrading –
Matt Helgeson, Bill Graves, David Grewell,
Iowa State University
Zein – protein from
Early 1900’s – used
in making shellac
Current use in
industry and food
The material is a powder (like corn
Mixed with small amounts of glycerol
(plasticizer) and ethanol (solvent)
Zein is hydrophobic (water-hating)
Products made from it are water-
Pots degraded by soil microbes
Zein is 10% protein – could release
nitrogen during decomposition
Pots filled with peat-based substrate
Pots filled with
perlite did not
Must use organic substrate with zein-
Treatment Total nitrogen (mg/kg)
Thin zein pot 82.6
Thick zein pot 120.5
Peat-based substrate 165.8
Zein protein contains 10% nitrogen
Peat moss enhances microbial breakdown of zein
Sterilization did not
Lack of oxygen in
Peat and fiber pots did
These are pots that have degraded
significantly after only a few months in soil
Zein degrades completely in organic
Zein-based pots are compostable without
the need for special equipment or
Zein-based pots increase substrate
fertility as they degrade
How do plants respond to zein-based bioplastic pots?
with zein pot
with zein pot
Transplants in zein pots are stunted in growth
Are plants kept in the zein pots suffering from root restriction?
Something is limiting growth in zein pots
Root systems of plants after 6 weeks of growth in an 8” azalea
Is something phytotoxic released by zein pots?
Plastic pot Peat pot Zein pot
R K R RK K
Something is delaying root growth in zein pots
+ N + N-N -N -N -N+ N + N
Zein pots raise ammonium, EC, pH levels
of potting substrate
These levels delay root growth
Supplemental N fertilization not needed
with zein pots!
Reformulation of zein pots to cut down on the
Will try fillers such as cellulose, coir (coconut)
fibers, and corn stover
Add chemical cross-linking agents or
plasticizers to slow down the biodegradation
Current longevity about 3 months –
suitable for bedding plants
May aid establishment of
crops transplanted or installed with their