Ask UConn Extension

Soil-biodegradable plastic mulch: Is it right for you?

By Shuresh Ghimire, UConn Cooperative Extension and Andy Radin, URI Cooperative Extension

Something important for you to consider: your use of plastic mulch in vegetable production. This is especially worthy to think about given that plastic mulch isn’t just for tomatoes, peppers, and eggplant anymore. Most small-scale growers use it for onions, lettuce, herbs, and more. You’ve no doubt heard about biodegradable mulch, but possibly not so great things. Here are some important questions you may have, and some real answers.

  1. Can plastic mulch actually “degrade?” Yes, and No.

First, the NO.

Degradation caused by sunlight, heat, moisture, and mechanical stress results in ever-smaller fragments of plastic, ultimately becoming what are called “microplastics.” According to a quick search on Google Trends, this word as a topic has increased dramatically over the last 5 years, which corresponds to an increase in our understanding of just how pervasive these pollutants are on land and in the oceans, and the possible and probable effects they have on species richness and diversity. It’s a disturbing and inescapable fact that plastics are changing the planet for the worse.

Now for the YES!

Degradation of plastic by microorganisms, known as biodegradation, is very much a real thing, provided the plastic is made of the polymers that microbes can consume. Soil-biodegradable plastic mulch breaks down into CO2, water, and microbial biomass.

But let it be stated right here up front: except for paper-based mulches, there are no biodegradable plastic mulches that are approved for use by certified organic farms in the United States. (See Box with NOP standards for reasons why.) If you are a certified organic grower, you cannot make the switch. You are permitted to use paper-based mulches, as long as they do not contain any synthetic materials. However, as they reduce the soil temperature, these do not perform well in our cold springs and early summers when warmth is desired. Further, our (usually) plentiful rainfall and warm summer weather causes rapid breakdown of these materials.

But if you otherwise do use plastic mulch, please read on as we consider a list of potential issues with the use of soil-biodegradable mulch (BDM.)

  1. How much do BDMs break down during the growing season?

Ghimire et al. (2018) found that among 4 products they tested for pumpkin production for two years in Mount Vernon, WA and Knoxville, TN, by the end of the season, less than 8% of the soil originally covered became exposed in Mount Vernon, and that was less than 25% in Knoxville. At Mount Vernon, the 2-year average daily air temperature for the pumpkin growing season (June–September) was 63 °F, RH was 76%, and total rainfall was 6 inches (4 inches in year 1 and 8 inches in year 2). At Knoxville, the 2-year average daily air temperature was 77 °F, RH was 80%, and total rainfall was 10 inches (14 inches in year 1 and 5 inches in year 2). These mulches really hold up during the season they are applied!

rows of vegetables covered in white biodegradable mulch
A variety of vegetable crops grown on BDM in Gresczyk Farms in Litchfield, CT. Photo: Shuresh Ghimire
  1. How do yields on BDM compare to yields on polyethylene (PE) mulch materials? list of USDA National Organic Program Rules

Our team also looked at that over several years and found relatively similar yield results between BDM and PE mulch. Unfortunately, it’s difficult to state this definitively because in a survey of comparative studies, Martín-Closas et al. (2017) found better performance, worse performance, and equal performance between BDM and PE. But these were in a wide range of soil and climate conditions. The chances of BDM performing better than PE in an exceptionally wet summer in eastern North Carolina are slim- the stuff will break down more rapidly, so you do take something of chance there.

  1. Will last year’s mulch bits disappear by the time I am prepping beds this coming year?

Visual assessments of macroscopic BDM fragments (>2.36 mm) show that after 4 years of annual BDM application from 2015 to 2018 in northwest Washington, mulch recovery from soil in spring 2019 ranged from 23 to 64% of the amount applied (area basis), indicating there was no accumulation of mulch fragments in the soil even after repeated applications (Ghimire et al., 2020). Recovery further decreased to 4-16% (mass basis) 2 years after the final mulch incorporation in fall 2020 (Griffin-LaHue et al., 2022). Only paper BDMs (e.g. Weed Guard Plus) show 100% biodegradation within the timespan of this study, but the conclusion from the study was that BDMs are degrading and do not accumulate in soil after repeated use. The longevity is strongly influenced by soil texture [see footnote], climatic factors (annual rainfall, annual average air temperatures), and product formulations. As you might expect, biodegradation is more rapid in warmer, wetter climates and in medium textured soils which have the benefits of good water-holding capacity as well as decent porosity.

Yes, there is differential breakdown among the products, and some of it remains for up to a few years. Products that perform the best within a season also probably leaves residues for longer. These are often thicker. But that doesn’t mean it leaves behind microplastics. The limits of instrumentation make it nearly impossible to document the final-most end-stage of decomposition of soil biodegradable plastic, whereas microplastics are actually detectable.

  1. Isn’t BDM more expensive than PE mulch?

Yes, it really is more expensive to purchase the material- two to three times more, depending on thickness. Plan to lay out more cash on the front end of the season. BUT: don’t forget to calculate how much you can save on the back end. There’s an easy to use calculator available for download here. [Note: this link will take you to an Excel spreadsheet on your browser tab. You can download it by clicking on the “File” menu in the upper left-hand corner of the spread sheet and then click on “download.” After doing that, make sure that you enable the macro features.]

Below is what the calculator generated based on using 3- three-thousand-foot rolls of mulch on an acre. There are many assumptions built into this output, and the spreadsheet allows you to adjust all of those. But going with what they filled in for default estimates (labor rates, tractor time, dumping fees, and more), take a look.Per Acre Cost Comparison chart

In this case with all of the default values they started with (again, which you can adjust), it costs 11% more per acre. In case you’re wondering, many of the dollar values they used are on the generous side, so this may be an over-estimate. Over-estimating is always good in enterprise planning, at least to a point.

Other factors not accounted for in the spreadsheet:

  1. Aggravation/Procrastination factor: there’s nothing like an un-fun job to persuade you to do other things that seem less aggravating. But pulling out the drip tape is the only thing stopping you from disking over your plastic-mulched beds.
  2. Interference with timeliness of cover crop planting: getting those beds cleaned up speeds you towards getting your cover crop seed planted. Getting deep into the financial analysis, it’s entirely possible that the earlier cover crop planting recovers more nutrients and increases organic matter in your soil, which are things you can take to the bank.
  3. If you grow into the fall and winter, you have tunnels to clean up but also fall planting deadlines to keep. Deadlines like that can easily cause a delay of field cleanup because every day of waning daylight in mid to late September reduces fall tunnel crop growth.
  4. You are putting less polyethylene mulch onto the land and eventually, into the ocean. Hard to calculate costs associated with that, but they are real.
  5. Can it be applied in the field just like PE mulch?

Yes, more or less BUT three caveats:

  1. It is more delicate than PE so it has to be handled a little more gently.
  2. If it does get damaged while laying it down, decomposition will be accelerated
  3. MOST IMPORTANT- it should not be applied as tightly as PE mulch because it continues to tighten as the weather warms. If it is installed too tightly at first, it will split as it tightens up, and this will allow early summer weeds to take over.
  4. What are the common experiences of the growers using BDM in Connecticut?
  • PE mulch leaves more fragments in the field than BDM
  • The purchasing cost of BDM is greater than PE, so BDM appears to be expensive in the beginning of the growing season, but overall BDM is cheaper after accounting for disposal costs
  • Growers can prepare the field for cover crops at the end of the season when the crop is grown with BDM; the mulch is disked/harrowed in after the drip tape is removed, which does not require much extra field work. But in years with wet Fall, cover crops are delayed or cannot be planted when PE mulch is used
  • Even with mulch deterioration in the later season, no/minimal weed growth occurs
  • Some growers shared experience of mulch adhesion with cantaloupe, but has not affected marketability of crops
  • Removal of PE mulch and picking up fragments at the end of the season is the least liked job of growers
  • Weed control and yield is comparable between BDM and PE mulch
  • They do not have any concern with BDM fragments after incorporation in the field as their observation is that BDM degrades in a couple of years
pepper plants growing in rows covered by white biodegradable mulch
Pepper grown on BDM in Cold Spring Brook Farm, Berlin, Connecticut. Photo: Shuresh Ghimire

Think it over- it could change things for your late summer-into-fall transition… for the better. For a video testimonial from a Connecticut farmer, watch this video.

You still have questions about BDM, this FAQ FAQs about BDM might help.

Footnote: We did not specifically look at the relationship between soil texture and mulch biodegradation rate. However, a study from Brazil (Duarte et al. 2019) reports that the CO2 production was much higher when a biodegradable mulch was tested in sandy-loam textured soil compared to clay and sand-textured soil. In general, degradation rate would be higher in the soil where there are greater populations of microbial communities, the soil is not too dry or not too wet (balance of water and air in the soil pore/capillaries). This probably means greater degradation rate in sandy loam or silty loam soil than clay or sands.

Useful links

Beware of Poison Ivy

poison ivy leaves
Warmer weather encourages many types of outdoor activities, it pays to be aware of certain plants that can make the outdoor experience unpleasant. Poison ivy leads the list of plants that cause skin irritation, or dermatitis. For those who are very sensitive to the effects of the oil produced by the poison ivy plant, direct contact with the plant can require medical attention. More information from our UConn Home & Garden Education Center is at s.uconn.edu/poisonivy
 
#poisonivy #askuconnextension

Using Coffee Grounds in Your Garden

wooden spoon with coffee grounds on it

We are frequently asked if coffee grounds can be used in a garden. The short answer is yes, coffee grounds can be used in garden soil!

Coffee grounds contain some major nutrients (nitrogen, phosphorus, and potassium) as well as some micronutrients, so put them to work in your garden. Allow them to dry and then spread them around the base of plants.
Apply no more than one-half inch of coffee grounds when putting fresh coffee grounds directly to the ground as mulch. Because coffee grounds are finely textured and easily compacted, thick layers of coffee grounds as mulch can act as a barrier to moisture and air movement in soils.
So if you are using coffee grounds as a “dressing” for specific plants or trees, apply the grounds in a thin layer or work into the top layer of the soil.
Article by Gail Reynolds, Middlesex County Master Gardener Coordinator

Seedlings in a Lawn

seedling infographic

Friend or foe? What are those seedlings coming up in your lawn? We are getting numerous calls and e-mails from people all around the state about seedlings coming up in their lawns and gardens. They believe, or are being told, that these are poison ivy, when in fact they are maple seedlings.
 
People need to check the leaves carefully – poison ivy is in threes, maples seedling have two leaves.
 
Some people do not want to mow their lawns for fear of being exposed to poison ivy. This is a mast year for certain maples, that is why there are so many.
 
Thanks to Pamm Cooper of our UConn Home & Garden Education Center for answering this question for us.
 
#AskUConnExtension

Joro Spider Information

joro spider
Photo by Dorothy Kozlowski, University of Georgia
You asked, we answered. We’ve been getting questions about Joro spiders. Gail Reynolds from our UConn Extension Master Gardener program answered:
Joro spiders, Trichonephila clavata, have been sensationalized in recent news stories. The actual appearance of these spiders in Connecticut has not been documented. According to various reports, this spider was first noted in Georgia in 2014. Its arrival was most likely through imported shipping and/or plant materials. The Joro spider is native to China, Japan, Korea, Southeast Asia, and the eastern part of India.
The spider has not spread quickly and is found in northern Georgia, western South Carolina, and extreme southern North Carolina.  They have been found in much lesser numbers in Tennessee and Alabama.
Most scientific assessments of this spider do not think the spider, or its eggs, can survive in colder temperatures of New England winters except perhaps for milder coastal areas.
The spider moves by spinning silk threads, which get caught by the wind and dispersed. The spider is only very mildly venomous and must be specifically provoked to bite.
Research has yet to determine if the Joro spider will displace any native spiders from their habitats or if they can all co-exist. University of Georgia scientists have reported that Joro spiders will capture and eat adult brown-marmorated stink bugs, another invasive insect and crop pest.  Native spiders will not prey on the invasive stink bugs.
A good source for additional information:  https://extension.psu.edu/joro-spiders
 

UConn Extension & Wrack Lines Awards

UConn Extension

Bug on flower
Photo: Mallory L.

We are delighted to share that UConn Extension has received three national awards from the Association of Communication Excellence:

Gold Award – Marketing – Budget Under $1000: Bug Week – Kara Bonsack and Stacey Stearns
Silver Award – Marketing – Budget Over $1000: Ask UConn Extension – Kara Bonsack, Stacey Stearns, Mike Zaritheny and Eshan Sonpal
Bronze Award – Writing for Newspapers: Stacey Stearns – “When Did GMO Become a Dirty Word”
Congratulations to our award recipients!

Wrack Lines Magazine: Connecticut Sea Grant

Wrack Lines Spring-Summer 2019 cover

The Spring-Summer 2019 issue of Wrack Lines magazine has received a Grand Award in the APEX 2020 Awards for Publication Excellence. The magazine focuses on climate change issues faced by residents along the coast, highlighting how “People and Nature Intertwine in New Ways”.

Congratulations to all the writers, photographers, editors and graphic designers!

Read the issue here.

Read more about this award: Wrack Lines issue receives APEX 2020 Gran Award 

What is It?

Spotted Pine Sawyer BeetleWhat is it?

The Spotted Pine Sawyer Beetle. It is right on time with adults appearing in June. It’s look alike is the Asian Longhorn Beetle, but the adult stage for the ALB occurs during August, says Carol Quish from our UConn Home & Garden Education Center.

Ask us your question at: http://bit.ly/AskUConnExtension_form

Our colleagues at University of Maine Cooperative Extension have a fact sheet with more information: https://bit.ly/BeetleFactSheet

Photo: Bruce Shay

#AskUConnExtension

Common Garden Mistakes

vegetable sprouting out of soil with words common garden problems written on the photoMistakes are a great learning tool, but they also can dampen any enthusiasm for a new project. When early mistakes compound problems further down the road, they can turn someone away from a pastime that offers great satisfaction, healthy activities and a renewed appreciation of the natural world around us.

So, if you are just starting on the gardening odyssey, let’s look at how to avoid a few common mistakes. Avoiding these trouble spots will make gardening easier, much more productive – and fun!

There are three main components to consider when starting out: sun, soil and water. In simpler terms, location, location, location. If you provide your garden the right combination of these three items, you sidestep many problems that can occur as the growing season progresses. These concepts apply to both vegetable and ornamental gardening, and to any specific type of plant you want to grow.

Let’s start with sun. Different plants have different light needs. Plants are categorized as sun, part sun/part shade and shade – but what do those labels mean? Here’s the breakdown. Full sun means at least six to eight hours of full sunlight a day and you start calculating that after 10 AM. Early morning sunlight isn’t considered strong enough to be included in your calculations.

Part sun/part shade is four to six hours of sun daily and anything less than four is considered shady. Make these calculations after the trees have leafed out in the spring; the sunlight in your yard shifts from winter to summer.

Your soil is the foundation of your garden, both literally and figuratively. It provides support, nutrients and water to your plants. Just like humans, different types of plants have different preferences in nutrition and water. Find out what you can provide and choose plants that will thrive in those conditions. First and foremost, if the site is new to you, or it’s been at least five years since the last one, get a soil test. Find out what you do – and don’t – need to add to your soil. Soil tests are available from the UConn soil lab at http://www.soiltest.uconn.edu/sampling.php

You can amend your soil with additional nutrients and elements, but it’s difficult to significantly change water-holding capacity. The test will help you determine how well your soil holds or drains water, allowing you to choose plants that are happiest in those conditions. Observation will also tell you a lot: how quickly does an area drain after a rainstorm? Is it wet is spring, but dry in the summer? Is it always damp?

A related issue is access to water. While an established plant in the right location may not need any supplemental water, both vegetable gardens and newly planted ornamentals will. Is it easy to get water to this area? Do you need to develop a water storage system, such as rain or water barrels? Or is another location really a better overall choice?

Once you know the characteristics of your space, you can then choose plants that will do well in that location without a great deal of extra work. The old phrase ‘Right Plant, Right Place’ is a valid one. Don’t try to significantly alter the location for a favorite plant that really isn’t right for the spot. It will only lead to frustration and poor results. Instead, find plants that like your location and choose from those. Let your gardening provide a positive experience!

For answers to your gardening questions, go to https://mastergardener.uconn.edu/ask-us-a-question/  . We’ll be happy to help!

Article by Sarah Bailey, UConn Extension State Master Gardener Coordinator

Ask UConn Extension Your Questions

Indu
Indu Upadhyaya, Food Safety Assistant Extension Educator. Photo: Kevin Noonan

UConn Extension has collaborated with our partners, communities and stakeholders for over 100 years. We are proud to serve all 169 cities and towns in Connecticut. The worldwide pandemic involving COVID-19 (coronavirus) has produced unprecedented challenges in the UConn community and around the world. Our services continue during this challenging time.

We are still delivering the science-based information you need. We are ready to answer your questions. Consult with us by email or on the phone. All of our educators are working and ready to serve you. Ask us a question online.

We are developing virtual programs to offset canceled in-person learning Abby Beissingeropportunities. Our educators are writing and updating fact sheets and other information. You have access to educational materials on our YouTube channel. We are growing our suite of online resources every day to meet the needs of our communities and stakeholders.

UConn CAHNR Extension educators have curated resources related to COVID-19 for our statewide audiences, including families, businesses, and agricultural producers.

Resources for all audiences includes:

  • Food safety and cooking
  • Hand washing and sanitizers
  • Infection prevention
  • Financial advice
  • Listings of open farms/farmers’ markets and school emergency meal distribution

Parents and families with children out of school can use the resources from our UConn 4-H program to provide new educational activities for youth. Activities available will keep youth engaged and learning and are appropriate for a variety of age groups.

Bruce Hyde presenting at Land Use Academy
Bruce Hyde presenting at Land Use Academy.

A list of resources has been collected for Connecticut businesses. It is a clearinghouse of resources, and not an official site. Business owners can connect to the state resources we provide for official and legal advice.

Agricultural producers are still working on farms, in greenhouses and along the coast in Long Island Sound during the COVID-19 outbreak. Extension educators have developed resources for specific agricultural sectors, including fruit and vegetable farms, aquaculture, and nursery and landscape professionals. Links to important updates from the Connecticut Department of Agriculture also are available.

Our Extension educators are updating and adding resources regularly. Please visit http://bit.ly/COVID-19-Extension.

We are also ready to answer your other questions, including:

  • How do I get my water tested?
  • What is wrong with my plant?
  • Can I eat healthy on a budget?
  • How does my son/daughter join 4-H?

UConn CAHNR Extension has more than 100 years’ experience strengthening communities in Connecticut and beyond. Extension programs address the full range of issues set forth in CAHNR’s strategic initiatives:

  • Ensuring a vibrant and sustainable agricultural industry and food supply
  • Enhancing health and well-being locally, nationally, and globally
  • Designing sustainable landscapes across urban-rural interfaces
  • Advancing adaptation and resilience in a changing climate.

Programs delivered by Extension reach individuals, communities, and businesses in each of Connecticut’s 169 municipalities.

We are here. We are ready to serve you.