Establishing native wildflower habitats in urban settings on a low budget

The total area of the study site was approximately 0.065 ha (0.16 acre), and it was selected in consultation with the private owner (details below). The plot was divided into three blocks with eight plots in each block. On each block, four plots received a dazomet treatment with tillage, and the other four plots received a no-till and glyphosate treatment. The plot area was approximately 16 m² (square shape of 3.96 m × 3.96 m) and separated on all sides by a 1.52 m buffer. The two chemicals used were dazomet (commercial product: Basamid G^™, active ingredient: dazomet 99%, AMVAC Chemical Corporation, Newport Beach, CA, USA) and glyphosate (commercial product: Ranger Pro^™, active ingredient: glyphosate 41%, Southern Agricultural Insecticides, Inc., Palmetto, FL, USA). The study was conducted from March 2020 to April 2022.

Site selection for wildflower plantings by public entities such as the state department of transportation or local governments involves the land that is available or that can be adopted for wildflower establishment. Therefore, the cost of land can be ignored from consideration in establishing a wildflower plot. For example, the strips along a divided highway cannot be developed or farmed. The nature of publicly owned land limits the site selection and affects the relative importance of ecosystem services that the wildflower plot provides. The shift emphasises the aesthetic benefits to the public rather than the measurable gains from, for example, pollination services (part of ecosystem services) provided by insects supported by the wildflower plot. Pollination services can be provided by foraging insects if a plot on public land is located near the farmland.

In the case of this study, the selected site was located at a multiple road crossing. The plot was covered with vegetation and occasionally mowed. The area was located in a mixed industrial–residential neighbourhood without any farmland nearby in an urban environment of the Atlanta metropolitan area in Georgia. The plot was property owned by Trilith Studios (461 Sandy Creek Rd, Fayetteville, GA 30214, Fayette County, USA; 33.4731086, -84.5099865; USDA Plant Hardiness Zone 8a-b) and within the range of sites used for wildflower plantings (Aldrich, 2002). The company volunteered to offer the site for the study. The site was previously used as rangeland and has remained fallow for at least two decades. The study site was an open field that extended 30 m at a slope of <5° towards a major roadway. The site was partly barren and partly covered in grass and weeds that would compete with the planted transplants.

To reduce weed competition, the plots were subjected to three separate applications of 1.5% glyphosate spray. Besides organic soil-preparation techniques such as grazing, solarisation, and burning, herbicide applications have been typical means of soil preparation, with glyphosate being the standard non-selective herbicide used to clear all vegetation in preparation of wildflower plantings (Johnston et al., 2015). Glyphosate targets actively growing plants (Kanissery et al., 2019) and is rapidly inactivated in soil (Quinn et al., 1988). Dazomet is a broad-spectrum pre-plant soil fumigant that has been used widely to control weeds and soil-borne pathogens in a wide variety of horticulture crops (Gilreath and Santos, 2004; Fennimore et al., 2008). However, it has not been studied in wildflower applications. For the glyphosate, the plots were sprayed using a hand pressurised backpack sprayer (Lesco 61840, Cleveland, OH, USA), with the first application until runoff. The first application yielded unsatisfactory results and was followed by two more applications. To enhance the effectiveness of treatment, the glyphosate mix concentration was increased to 5%. All three applications were performed prior to planting transplants on untilled soil. For the dazomet treatment, plots were roto-tilled with the attachment (Land Pride RTA3576, Salina, KS, USA) mounted on a tractor (John Deere 4600, Moline, IL, USA). The soil was tilled to a depth of 15.2 cm.

The tilling was followed by dazomet application at the manufacturer-recommended rate (181.44 kg per A) and another 15.2 cm tilling was done to incorporate it into the soil. The soil was packed using a roller (Brouwer BTR-30, Kesmac Inc., Keswick, Ontario, Canada). To activate the dazomet, the plots were irrigated with 25 mm of water as measured by randomly placed water gauges. Finally, to assure successful soil fumigation, the treated plots were covered with plastic sheeting (HDX 6 mm clear plastic sheeting, Home Depot, Atlanta, Georgia), and its edges were placed in 15.2 cm deep trenches dug around each treated plot. A compact utility loader (Toro Dingo TX-1000 Wide Track Vertical Lift, Bloomington, IN, USA) performed the tasks of digging and backfilling the trenches using a trencher attachment (Toro).

Plant material used in the study was cultivated in-house from seeds and planted as standard size landscape plugs. Seeds were acquired from Prairie Moon Nursery (Winona, MN, USA) (Table 4). Five criteria guided the selection of the 15 herbaceous perennial species: native status in the state of Georgia or the southeastern United States, purported pollinator value, suitability to grow in open areas, tolerance of wet to dry soil conditions and bloom time. A total of 15 native forb species were grown in a greenhouse at the research facility. Standard protocols for dormant seed and subsequent seedling establishment were followed. Plants (also referred to as plugs) were grown in 11.43 cm pots. Although this site used plugs raised from seed, the calculations show the plug prices listed by commercial vendors recognising that many lack the capacity to produce their own plugs and have to rely on purchases.

Plants were planted on 28 September 2020 in a triangular shape (measuring 76.2 cm) in 15.2 cm diameter holes, 25.4–30.5 cm deep dug by a soil auger diameter (Stihl, Waiblingen, Germany). A total of 720 transplants were planted, including plants – 360 for one method – applying dazomet treatment, and 360 for the other method – preparing no-till and glyphosate treatment. Each method consisted of 24 replicates of 15 wildflower species. There were 30 plants in each plot. The soil was neither amended during or after planting with nutrients or organic matter; this is the standard recommendation for native perennial plantings (Ullmann et al., 2016). Adding organic matter or soil amendments would also increase costs of establishing the wildflower plot.

The first 3 weeks after planting, plants were irrigated by a hose attached to a water truck with 25 mm per plant. No supplemental irrigation was applied beyond the initial establishment phase. Natural precipitation over the study period totalled 123 cm (October 2020 through August 2021, data extracted from Georgiaweather.net).

Labour is necessary to establishing a wildflower plot using plugs. This study estimates the labour costs using publicly available wage figures for the first year of the study. Median wages are typically used to calculate labour costs because mean wages are affected by outliers (Hara et al., 2018). Landscaping, lawn service or groundskeeping supervisors earn a median wage of $24.52 and a mean wage of $25.98 per hour (Bureau of Labor, 2020). Additionally, the average landscaping and groundskeeping worker earns a median wage of $15.26 and mean wage of $16.25 (Bureau of Labor, 2020).

The establishment of wildflower plots involves simple equipment dictated by the specific location and is commonly limited in size. Each piece of equipment used during the preparation, planting and maintenance of the beds in the current study was recorded. Pricing of the equipment was based on the average cost of each piece of equipment sourced from online databases, field representatives and retail stores. The time spent using each piece of equipment on the site was recorded. Labour costs were calculated using industry averages provided by the Bureau of Labor Statistics. All calculations were done in Microsoft Excel^® (Microsoft Corporation, Redmond, WA, USA).

Dazomet use requires the presence of a certified applicator (Basamid G^™ Label) and specialised machinery. A team of two landscaping workers and one supervisor was required to properly till the soil and apply the dazomet. In this study, the three workers required 5 hr and 40 min to till the treated beds, incorporate the dazomet, repeat the till, apply supplemental irrigation and cover the soil with plastic sheeting to seal in the active ingredient (Figure 1). Dazomet application and sealing the treated surface with the plastic sheathing were particularly labour-intensive.

Figure 1.

The cost of dazomet involves only the amount applied at the site. Manufactured by AMVAC Chemical Corporation, dazomet is sold under the commercial name of Basamid G. Given the expected amount needed for application, a 22.68 kg container with N active ingredient dazomet 99% was most suitable for the experiment. With a price of $400 per bag (AI 90% dazomet), only 8.44 kg were applied at the cost of $148.98.

Using the Bureau of Labor Statistics wage data, the median wage rates were applied in the calculations since the average wage rate could be distorted by the most extreme (lowest and highest) rates. The labour cost associated with the treatment method involving dazomet application was $311.52. To illustrate the total labour cost (the hourly cost of performing tasks listed in Figure 1), an industry standard overhead of 30% was added yielding the total labour costs of $404.97 (Table 3).

Table 1 shows the equipment necessary for the scenario applying dazomet and the required soil tilling. Two pieces of equipment, a wide track and a tractor, accounted for the majority of equipment costs. The addition of two attachments supplemented the most expensive pieces of machinery. The source of the price information about the machinery was a popular hardware and horticulture store chain.

The initial time-consuming task involved the measurement and mixing of the herbicide in the tank. The first application of herbicide mix was critical and its implementation required a full hour (Figure 2). The two subsequent applications of glyphosate required only one half the time used in the first application. Glyphosate spraying, applied prior to plot tilling, required 3 hr and 30 min of labour for three applications. Glyphosate was applied using a backpack sprayer. The use of a backpack sprayer involved physical effort, but the method eliminated emission drift that was risked with the use of a tractor.

Figure 2.

The labour costs associated with the glyphosate application and no-till approach to plot preparation (Scenario 2) were less than in the case of the dazomet treatment and involved only one worker. Direct labour costs estimated at $53.41 were calculated using figures provided by the Bureau of Labor Statistics. Adding the industry standard overhead of 30% established the total labour costs of three glyphosate applications as $69.43 (Table 3). The difference in labour costs under Scenario 2 is substantial and may appeal to those who would like to establish wildflower plots but may lack adequate labour resources.

The implementation of Scenario 2 (‘no-till and glyphosate’) requires a minimal amount of simple equipment (Table 2). The scenario’s implementation required 3 hr and 30 min (Figure 2). The mixed herbicide is applied using a backpack sprayer. The application also requires the purchase of a retail size container of glyphosate, but only a portion of the purchased volume is applied given the size of the plot. Given specific locations, the party establishing a wildflower plot may select a different size of the herbicide container to avoid the need for storing the unused portion.

Table 3 shows the summary of the labour and chemical costs of both scenarios. Scenario 2 offers lower costs than Scenario 1 for establishing wildflower plots using transplants. The primary cause of cost difference is the choice of equipment. The use of the backpack sprayer in the current study is justified by the size of the plot and applicable only to small sites.

Choosing Scenario 1 is practical if the services associated with the plot preparation can be performed using rented equipment. Outsourcing to a landscape firm could also offer savings if the firm has trained workers and specialised equipment. Knowledgeable civic organisations could also volunteer their services in establishing wildflower plots. The calculations presented in the current study serve as a benchmark in choosing a course of action.

The cost difference between the two different treatments does not account for several additional factors. First, the equipment used in both treatments can be used repeatedly for a number of years for other projects. In 1988, a study found that tractor repair costs equal 80% of the tractor’s initial purchase price after 10,000 hr of use (Morris, 1988). To reach a 10,000-hr limit, a tractor would have to be used 50 hr a week for 200 straight weeks. Technology has advanced considerably since 1988 and with care and regular maintenance, equipment lasts for many years. Tractors, tillers and backpack sprayers required for dazomet applications should be considered investments that are paid off over time through repeated use. Second, the choice of the scenario implies the use of different herbicides. Dazomet costs more than glyphosate. Additionally, dazomet requires the presence of a certified applicator to supervise its application. A certified applicator must complete advanced training in the United States and the labour cost could be higher given their expertise, increasing Scenario 1 labour costs.

Each of the 24 replicate plots was planted with two plants of 15 wildflower species each as 11.43 cm plugs, for a total of 30 plants per plot. The plugs were evenly divided and planted in plots treated with dazomet and plots treated with glyphosate. Plugs cost $519.25 per treatment, using the listed prices from commercial vendors and assuming the investor in the wildflower site lacks the capacity to raise plugs from seed (Table 4). The price per plug includes the cost of labour involved in planting and care during growth, plug packaging and shipping and distribution. The risk premium for having non-viable seed, loss or damage prior to delivery is embedded in the price and cannot be isolated as a separate cost item. It appears that the transfer of that risk to the plug supplier is advisable.

The planting of plugs involved drilling holes to a depth of approximately 25.4 cm using a Stihl BT131 auger with a 15.2 cm drill bit by one landscaper. Another landscaper randomly selected a plug and manually planted it in the drilled hole. The method required 4.5 hr per landscaper to complete planting at $68.67 per worker. After the addition of 30% overhead costs the estimated labour cost is $178.54.

All 15 species established well and experienced significantly reduced weed pressure under the dazomet treatment. Additionally, over 90% of the transplants grown under Scenario 1 (till + dazomet) were still viable by the conclusion of the current study, while 85% of the transplants were alive under Scenario 2 (no-till + glyphosate). The pairwise test on difference between till vs. no till treatments confirmed the statistical difference between them with p-value = 0.0001454 and α = 0.05. Though the statistically significant, in practical terms, 85% survival is acceptable. While the higher growth indices under the former treatment were attributed to increased rootable soil volume (due to tillage), plant survival rates under both treatments were achieved with no additional maintenance after the initial planting and watering, without any fertiliser, mulch application or manual weeding. Limited maintenance and fertilisation reduces CO₂ emissions (Marshall et al., 2023). Therefore, both planting approaches are consistent with the goal of sustainability and low-cost maintenance once the urban wildflower plots were established.