Final report for FNE23-054
Project Information
This project sought to identify the optimum weed-suppression technique for the community farms that T6B operates. T6B selected six areas of our farms to install three styles of treatments to study over the course of the 2023 season. The experimental groups were as follows:
- Wood chips applied 3”-5” thick.
- Thin construction cardboard (X board) measuring 0.021” thick below a 3”-5” thick layer of wood chips.
- Thick construction cardboard (Ram board) measuring 0.042” thick below a 3”-5” thick layer of wood chips.
We analyzed the following metrics:
- Weed Volume: Weed burden was quantitatively measured by volume using standardized 15-gallon buckets. Since single treatment areas were weeded several times over the course of the season, cumulative weed volume was recorded for each treatment area over time.
- Photography and Identification: Treatment areas were photographed before weeding. Weed species were identified and recorded.
- Labor Hours: Labor hours were recorded for both treatment installation and weeding.
In conclusion, we find that X Board and Ram Board covered in wood chips are highly effective weed suppression methods that far outcompete the use of wood chips alone during peak growing season. Though these methods were more expensive to install, the added benefit of reduced weeding labor quickly made them cost effective when compared to wood chips. Additionally, both methods were able to completely suppress any weeds during the fall and winter months over the first few months.
The results of this study will be applicable to all similarly situated urban farms in Baltimore and beyond and we plan to disseminate our learnings with our peers and partner organizations through the Farm Alliance of Baltimore.
This project seeks to identify the optimum weed-suppression technique for the community farms operated by The 6th Branch (T6B) in Baltimore City. The results of this study will be applicable to all similarly situated urban farms in Baltimore and beyond. The first objective is to analyze and identify three weed-suppression methods we will employ. (A sub-objective is that this experiment itself will be useful in controlling weeds during the 2023 growing season.) The second objective is to create an easily accessible report document that can be used by T6B staff and disseminated widely. The intent of this document is very specifically not to create an academic treatment of the compared weed suppression techniques. Rather, we will build a simple and direct field guide that shows our process, results, and provides recommendations to peer urban farmers.
T6B's community farming program is dedicated to producing the maximum quantity of high-quality food and distributing it directly to residents in East Baltimore. Our farms are all located adjacent to homes and playgrounds, and the farms themselves serve as community gathering spaces. Accordingly, we committed from the start to all-organic practices, both for environmental and health purposes because we do not want to expose the residents of our farming communities to chemical herbicides. This poses a unique challenge for suppressing weeds, especially the highly aggressive bermuda grass that grows on the formerly vacant lots where each farm is located.
Since 2013, we have tried multiple weed-suppression methods including: heavy mulching with wood chips and leaves, plastic covers, plywood and stones over pathways, and simply letting weeds grow and mowing them where possible. We have had varying degrees of success with these methods, each of which has still left us with a time-intensive burden to remove weeds on the farm, especially in pathways between growing areas. More importantly, we have never had the staff-time resources to record our experiences with weed-suppression or do anything more than learn anecdotal lessons from our work and peer farmers’ advice.
At our farms, we regularly fight bermuda grass in perennial boxed beds and at the perimeters of our in-ground beds. In 2023, we created a research project to study three passive and chemical-free ways of weed management: the standard wood chip mulch, and wood chip mulch layered on top of two different thicknesses of construction cardboard. This experiment and initiative served to determine the best non-chemical weed suppression techniques for the community farms T6B operates and other similar farms.
This project aimed to meet the sustainable agriculture goals of:
- Improved productivity, reduction of costs and/or increase of net farm income. Increasing the effectiveness of our weed suppression methods to substantially free up our farming personnel to concentrate on other essential farm tasks, rather than worrying about weeding or mowing pathways.
- Conservation of soil, improvement of water quality, and protection of natural resources. Effective weed suppression techniques to preserve the soil at the farms by preventing runoff and eliminating the bermuda grass.
T6B launched our community farming program in 2013 with the construction of the Oliver Community Farm. Since then, T6B built the Johnston Square Community Farm and Garden (2019) and broke ground on the new Broadway East Berry Farm in 2022. Our approach to community farming is based on the belief that the land we farm and food that is grown belongs to the communities in which each farm is located. We contribute our labor, logistical expertise, and financial support as a 501(c)(3) nonprofit to generate food, which we then distribute to East Baltimore neighbors. The food is distributed for free at market nights and through community association partners because the food already belongs to those who receive it. We grow and distribute 6,500+ pounds of fresh produce each year at an estimated in-kind value of $30,000+ annually, if we were to sell it at market rates.
The farming program encapsulates approximately 2.5 acres of farm space. Each farm is located on what was once a series of vacant lots following housing demolition that had been subject to frequent illegal dumping. We grow a wide variety of vegetables in-ground and in raised planter beds. Each farm is studded throughout with fruit trees. There are no animals at the farms. We operate each farm using entirely organic practices, without chemicals.
Leading our program is Liz Lamb, our Community Farming Program Manager, who has 6+ years' experience farming and is originally an engineer by training. We also have a part-time farming associate and paid intern who regularly support the farming program. And, T6B hosts approximately 1,500 volunteers per year on the 20+ acres we steward, most of whom volunteer at one of the farm sites.
Cooperators
- - Technical Advisor
Research
Our farming program operates two farms (and a third under construction) with one full-time staff member, two part-time staff members, and a host of volunteers. Accordingly, our methodology was designed to be simple enough to manage at our capacity-level across multiple sites. T6B selected six areas of our farms to install three styles of treatments to study over the course of the 2023 season. The areas included 3’ wide perimeter strips around the boxed beds, a sinuous path through a park area, and a circular space surrounding several boxed beds.
Experimental Groups:
- Wood chips applied 3”-5” thick.
- Thin construction cardboard (X board) measuring 0.021” thick below a 3”-5” thick layer of wood chips.
- Thick construction cardboard (Ram board) measuring 0.042” thick below a 3”-5” thick layer of wood chips.
Study Metrics:
- Weed Volume: As needed, the treatment areas were weeded to completion. Weed burden was quantitatively measured by volume using standardized 15-gallon buckets. Since single treatment areas were weeded several times over the course of the season, cumulative weed volume was recorded for each treatment area over time.
- Photography and Identification: Treatment areas were photographed before weeding. Weed species were identified and recorded.
- Labor Hours: Labor hours were recorded for both treatment installation and weeding.
Data Analysis:
Cumulative weed burden was normalized to 1000 square feet (sqft) for each treatment area, then was plotted against time from installation for each treatment. The data was fit using a linear regression equation [Volume = k * Days] for the mulch only treatment and an exponential growth equation [Volume = Volume0 * e ^ (k * Days)] for both cardboard treatments. Statistical significance between the regression equations for each cardboard treatment was performed using an extra sum of squares F test. Break even cost analysis was performed using the following equation: [Cost = MaterialCost + (InstallationLabor + WeedingLabor) * LaborCost], assuming LaborCost = $15/hr, and with average labor times for InstallationLabor (40hr/1000sqft) and WeedingLabor (2hr/bucket) derived from actual data.
The treatments were installed across four sites in the spring. Over the course of spring and summer, we completed eight sessions of weeding. More than 370 15-gallon buckets of weeds were removed from study areas. The installation and weeding took over 54 hours of group volunteer time, equating to more than 1000 individual person hours. After exciting initial results, a second study area was installed in the fall for both cardboard treatments to monitor their effectiveness in the fall and winter months.
Weed Types:
The most common weeds identified included bermuda grass, chicory, dandelion, bindweed, yellow sedge, and common thistle. Bermuda grass was the predominant weed comprising more than 4/5 of all the observed weeds. Weed type was not affected by treatment.
Weed Volume:
The trendlines for the spring installations show considerably more weeds grew through the control treatment of only wood chips. Both cardboard treatments had a lengthy delay in the initial appearance of weeds (~40 days) compared to wood chips alone (~20 days). Ram Board marginally outcompeted X Board in the later days of the experiment, however this effect was not statistically significant (p=0.55). Additionally, the data suggest a loss of effectiveness for both cardboard treatments over time since the rate of weed growth increased in the later days of the experiment. No weeds grew in either the X Board or Ram board treatment areas installed in fall through the new year.
Cost Analysis:
We found similar labor costs were required for the installation of all three treatments over a similar area. However, in our region, oftentimes wood chips can be delivered to the farm for free whereas the cardboard treatments required a significant upfront investment (X Board: $150/1000sqft, Ram Board: $250/1000sqft). Nevertheless, the cost of weeding labor far outweighed the initial installation costs, and our modeled cost analysis found X Board and Ram Board to be cheaper than wood chips alone after 12 and 13 days respectively.
In conclusion, we find that X Board and Ram Board covered in wood chips are highly effective weed suppression methods that far outcompete the use of wood chips alone during peak growing season. Though these methods were more expensive to install, the added benefit of reduced weeding labor quickly made them cost effective when compared to wood chips. Additionally, both methods were able to completely suppress any weeds during the fall and winter months over the first few months.
If a farm has access to the high volume of volunteers T6B regularly works with and the budget then we recommend using a construction cardboard product in conjunction with an application of wood chips. We hold the value that a clean and tidy farm is more welcoming to our neighbors and visitors, so for us the tedious process of weeding pathways is worth the outcome. We also believe that over time, these treatments will likely contribute to the eradication of bermuda grass from the subject areas, reducing future labor in each subsequent season. However, we recognize that not all farms have the same requirements for extremely low weed burden and may not see the same cost benefit with cardboard treatments.
Finally, we found that the thinner X Board did seem to degrade more quickly than the Ram Board which we believe to be the cause of the slight difference in weed suppression that we saw in the data. A future study with more regular weeding intervals as well as longer-term analysis over multiple seasons may be useful in identifying whether the added cost of Ram Board could be worthwhile over time.
Education & Outreach Activities and Participation Summary
Participation Summary:
We are currently developing an infographic to share our learnings from the study with our peers and partner organizations. Once this is ready, we will disseminate it through our online platforms as well as to the members of the Farm Alliance of Baltimore.
Learning Outcomes
T6B has nearly 10 years of working experience in urban farming and the constant struggle to keep weeds from overtaking even the smallest green spaces. As noted in our application, we have tried multiple methods to control weeds over this time. Our most successful recent effort has been to use recycled cardboard from shipping boxes (donated by our supporters and staff) under mulch. And while we appreciate the sustainability benefits of recycling cardboard in this way, we simply cannot obtain the volume of cardboard required to suppress weeds across all our farming sites. We have never before used ram board or X-board under mulch for weed suppression. This method had come recommended to us by peer farmers in Baltimore City.
The results of this study have helped our team and myself learn about the best practices for approaching weed suppression on our sites and has helped us make better decisions moving forward on how we allocate not only our dollars but also our time, ensuring that our labor is focused on activities that are most cost effective.
Project Outcomes
See above.
A future study with more regular weeding intervals as well as longer-term analysis over multiple seasons may be useful in identifying whether the added cost of Ram Board could be worthwhile over time.
Information Products
- The 6th Branch - Weed Suppression Fact Sheet (Fact Sheet)